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Reproductive technology
View on WikipediaReproductive technology encompasses all current and anticipated uses of technology in human and animal reproduction, including assisted reproductive technology (ART),[1] contraception and others. It is also termed Assisted Reproductive Technology, where it entails an array of appliances and procedures that enable the realization of safe, improved and healthier reproduction. While this is not true of all people, for an array of married couples, the ability to have children is vital. But through the technology, infertile couples have been provided with options that would allow them to conceive children.[2]
Overview
[edit]Assisted reproductive technology
[edit]Assisted reproductive technology (ART) is the use of reproductive technology to treat low fertility or infertility. Modern technology can provide infertile couples with assisted reproductive technologies. The natural method of reproduction has become only one of many new techniques used today. There are millions of couples that do not have the ability to reproduce on their own because of infertility and therefore, must resort to these new techniques. The main causes of infertility are that of hormonal malfunctions and anatomical abnormalities.[3] ART is currently the only form of assistance for individuals who, for the time being, can only conceive through surrogacy methods).[4] Examples of ART include in vitro fertilization (IVF) and its possible expansions, including:
- artificial insemination
- artificial reproduction
- cloning (see human cloning for the special case of human beings)
- cytoplasmic transfer
- cryopreservation of sperm, oocytes, embryos
- embryo transfer
- fertility medication
- hormone treatment
- in vitro fertilization
- intracytoplasmic sperm injection
- in vitro generated gametes
- preimplantation genetic diagnosis
Role of the Society for Assisted Reproductive Technology (SART)
[edit]In 1981, after the birth of Elizabeth Carr, the first baby in the United States to be conceived through in vitro fertilization (IVF). Her birth gave hope to many couples struggling with infertility. Dr. Howard Jones brought together the leading practitioners of the five US-based IVF programs (Norfolk,[clarification needed] Vanderbilt, University of Texas at Houston, and the University of Southern California, Yale) to discuss the establishment of a national registry for in vitro fertilization attempts and outcomes. 2 years later, in 1985 the society for assisted reproductive technology (SART) was founded as a special interest entity within the American Fertility Society.[5] SART has not only informed the evolution of infertility care but also improved success of antiretroviral therapy.[6]
Prognostics
[edit]Reproductive technology can inform family planning by providing individual prognoses regarding the likelihood of pregnancy. It facilitates the monitoring of ovarian reserve, follicular dynamics and associated biomarkers in females,[7] as well as semen analysis in males.[8]
Contraception
[edit]Contraception, also known as birth control, is a form of reproductive technology that enables people to prevent pregnancy.[9] There are many forms of contraception, but the term covers any method or device which is intended to prevent pregnancy in a sexually active woman. Methods are intended to "prevent the fertilization of an egg or implantation of a fertilized egg in the uterus."[10] Different forms of birth control have been around since ancient times, but widely available effective and safe methods only became available during the mid-1900s.[11]
Others
[edit]The following reproductive techniques are not currently in routine clinical use; most are still undergoing development:
Same-sex procreation
[edit]Research is currently investigating the possibility of same-sex procreation, which would produce offspring with equal genetic contributions from either two females or two males.[12] This form of reproduction has become a possibility through the creation of either female sperm (containing the genetic material of a female) or male eggs (containing the genetic material of a male). Same-sex procreation would remove the need for lesbian and gay couples to rely on a third party donation of a sperm or an egg for reproduction.[13] The first significant development occurred in 1991, in a patent application filed by U.Penn. scientists to fix male sperm by extracting some sperm, correcting a genetic defect in vitro, and injecting the sperm back into the male's testicles.[14] While the vast majority of the patent application dealt with male sperm, one line suggested that the procedure would work with XX cells, i.e., cells from an adult woman to make female sperm.
In the two decades that followed, the idea of female sperm became more of a reality. In 1997, scientists partially confirmed such techniques by creating chicken female sperm in a similar manner.[15] They did so by injecting blood stem cells from an adult female chicken into a male chicken's testicles. In 2004, other Japanese scientists created two female offspring by combining the eggs of two adult mice.[16][17]
In 2008, research was done specifically for methods on creating human female sperm using artificial or natural Y chromosomes and testicular transplantation.[18] A UK-based group predicted they would be able to create human female sperm within five years. So far no conclusive successes have been achieved.[3]
In 2018 Chinese research scientists produced 29 viable mice offspring from two mother mice by creating sperm-like structures from haploid Embryonic stem cells using gene editing to alter imprinted regions of DNA. They were unable to get viable offspring from two fathers. Experts noted that there was little chance of these techniques being applied to humans in the near future.[19][20]
Ethics
[edit]Recent technological advances in fertility treatments introduce ethical problems, such as the affordability of the various procedures. The exorbitant prices can limit who has access.[12] The cost of performing ART per live birth varies among countries.[21] The average cost per IVF cycle in the United States is USD 9,266.[22] However, the cost per live birth for autologous ART treatment cycles in the United States, Canada, and the United Kingdom ranged from approximately USD 33,000 to 41,000 compared to USD 24,000 to 25,000 in Scandinavia, Japan, and Australia[23]
The funding structure for IVF/ART is highly variable among different nations. For example, no federal government reimbursement exists for IVF in the United States, although certain states have insurance mandates for ART[24]
Many issues of reproductive technology have given rise to bioethical issues, since technology often alters the assumptions that lie behind existing systems of sexual and reproductive morality. Other ethical considerations arise with the application of ART to women of advanced maternal age, who have higher changes of medical complications (including pre-eclampsia), and possibly in the future its application to post-menopausal women.[25][26][27] Also, ethical issues of human enhancement arise when reproductive technology has evolved to be a potential technology for not only reproductively inhibited people but even for otherwise re-productively healthy people.[28]
In fiction
[edit]- Films and other fiction depicting contemporary emotional struggles of assisted reproductive technology have had an upswing first in the latter part of the 2000s decade, although the techniques have been available for decades.[29]
- Science fiction has tackled the themes of creating life through non-conventional methods since Mary Shelley's Frankenstein. In the 20th century, Aldous Huxley's Brave New World (1932) was the first major fictional work to anticipate the possible social consequences of reproductive technology. Its largely negative view was reversed when the author revisited the same themes in his utopian final novel, Island (1962).
References
[edit]- ^ Kushnir, Vitaly A.; Choi, Jennifer; Darmon, Sarah K.; Albertini, David F.; Barad, David H.; Gleicher, Norbert (August 2017). "CDC-reported assisted reproductive technology live-birth rates may mislead the public". Reproductive BioMedicine Online. 35 (2): 161–164. doi:10.1016/j.rbmo.2017.05.008. ISSN 1472-6483. PMID 28578895.
- ^ Al-Inany HG, Youssef MA, Ayeleke RO, Brown J, Lam WS, Broekmans FJ (April 2016). "Gonadotrophin-releasing hormone antagonists for assisted reproductive technology" (PDF). The Cochrane Database of Systematic Reviews. 4 (8) CD001750. doi:10.1002/14651858.CD001750.pub4. PMC 8626739. PMID 27126581.
- ^ a b MacRae F (February 2008). "Scientists turn bone marrow into sperm". Australia: The Courier and Mail.
- ^ Campo H, Cervelló I, Simón C (July 2017). "Bioengineering the Uterus: An Overview of Recent Advances and Future Perspectives in Reproductive Medicine". Annals of Biomedical Engineering. 45 (7): 1710–1717. doi:10.1007/s10439-016-1783-3. PMID 28028711. S2CID 4130310.
- ^ "Gosden, Prof. Roger Gordon, (born 23 Sept. 1948), Professor, and Director of Research in Reproductive Biology, Weill Medical College, Cornell University, 2004–10; Owner and Director, Jamestowne Bookworks, LLC, Williamsburg, Virginia", Who's Who, Oxford University Press, 1 December 2007, doi:10.1093/ww/9780199540884.013.u17652
- ^ Toner, James P.; Coddington, Charles C.; Doody, Kevin; Van Voorhis, Brad; Seifer, David B.; Ball, G. David; Luke, Barbara; Wantman, Ethan (September 2016). "Society for Assisted Reproductive Technology and assisted reproductive technology in the United States: a 2016 update". Fertility and Sterility. 106 (3): 541–546. doi:10.1016/j.fertnstert.2016.05.026. PMID 27301796.
- ^ Nelson SM, Telfer EE, Anderson RA (2012). "The ageing ovary and uterus: new biological insights". Human Reproduction Update. 19 (1): 67–83. doi:10.1093/humupd/dms043. PMC 3508627. PMID 23103636.
- ^ Narvaez JL, Chang J, Boulet SL, Davies MJ, Kissin DM (August 2019). "Trends and correlates of the sex distribution among U.S. assisted reproductive technology births". Fertility and Sterility. 112 (2): 305–314. doi:10.1016/j.fertnstert.2019.03.034. PMID 31088685.
- ^ Sunderam S, Kissin DM, Crawford SB, Folger SG, Boulet SL, Warner L, Barfield WD (February 2018). "Assisted Reproductive Technology Surveillance - United States, 2015". MMWR. Surveillance Summaries. 67 (3): 1–28. doi:10.15585/mmwr.ss6703a1. PMC 5829941. PMID 29447147.
- ^ "Definition of Birth control". MedicineNet. Archived from the original on August 6, 2012. Retrieved August 9, 2012.
- ^ Hanson SJ, Burke AE (2010). "Fertility control: contraception, sterilization, and abortion". In Hurt KJ, Guile MW, Bienstock JL, Fox HE, Wallach EE (eds.). The Johns Hopkins manual of gynecology and obstetrics (4th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. pp. 382–395. ISBN 978-1-60547-433-5.
- ^ a b Kissin DM, Adamson GD, Chambers G, DeGeyter C (4 July 2019). Assisted Reproductive Technology Surveillance. Cambridge University Press. ISBN 978-1-108-49858-6.
- ^ Gerkowicz SA, Crawford SB, Hipp HS, Boulet SL, Kissin DM, Kawwass JF (April 2018). "Assisted reproductive technology with donor sperm: national trends and perinatal outcomes". American Journal of Obstetrics and Gynecology. 218 (4): 421.e1–421.e10. doi:10.1016/j.ajog.2017.12.224. PMC 11056969. PMID 29291411. S2CID 27903207.
- ^ US 5858354 Repopulation of testicular Seminiferous tubules with foreign cells, corresponding resultant germ cells, and corresponding resultant animals and progeny
- ^ Tagami T, Matsubara Y, Hanada H, Naito M (June 1997). "Differentiation of female chicken primordial germ cells into spermatozoa in male gonads". Development, Growth & Differentiation. 39 (3): 267–71. doi:10.1046/j.1440-169X.1997.t01-2-00002.x. PMID 9227893. S2CID 35900043.
- ^ Kono T, Obata Y, Wu Q, Niwa K, Ono Y, Yamamoto Y, et al. (April 2004). "Birth of parthenogenetic mice that can develop to adulthood". Nature. 428 (6985): 860–4. Bibcode:2004Natur.428..860K. doi:10.1038/nature02402. PMID 15103378. S2CID 4353479.
- ^ Silva SG, Bertoldi AD, Silveira MF, Domingues MR, Evenson KR, Santos IS (January 2019). "Assisted reproductive technology: prevalence and associated factors in Southern Brazil". Revista de Saúde Pública. 53: 13. doi:10.11606/s1518-8787.2019053000737. PMC 6390642. PMID 30726494.
- ^ "Color illustration of female sperm making process" (PDF). Human Samesex Reproduction Project.[permanent dead link]
- ^ McRae M (11 October 2018). "Chinese Researchers Have Spawned Healthy Mice With 2 Biological Mothers And No Father". Science Alert. Retrieved 12 October 2018.
- ^ Li ZK, Wang LY, Wang LB, Feng GH, Yuan XW, Liu C, et al. (November 2018). "Generation of Bimaternal and Bipaternal Mice from Hypomethylated Haploid ESCs with Imprinting Region Deletions". Cell Stem Cell. 23 (5): 665–676.e4. doi:10.1016/j.stem.2018.09.004. PMID 30318303.
- ^ Chambers, Georgina M.; Sullivan, Elizabeth A.; Ishihara, Osamu; Chapman, Michael G.; Adamson, G. David (June 2009). "The economic impact of assisted reproductive technology: a review of selected developed countries". Fertility and Sterility. 91 (6): 2281–2294. doi:10.1016/j.fertnstert.2009.04.029. ISSN 0015-0282. PMID 19481642.
- ^ Peipert, Benjamin J.; Montoya, Melissa N.; Bedrick, Bronwyn S.; Seifer, David B.; Jain, Tarun (4 August 2022). "Impact of in vitro fertilization state mandates for third party insurance coverage in the United States: a review and critical assessment". Reproductive Biology and Endocrinology. 20 (1) 111. doi:10.1186/s12958-022-00984-5. ISSN 1477-7827. PMC 9351254. PMID 35927756.
- ^ Reindollar, Richard H.; Regan, Meredith M.; Neumann, Peter J.; Levine, Bat-Sheva; Thornton, Kim L.; Alper, Michael M.; Goldman, Marlene B. (August 2010). "A randomized clinical trial to evaluate optimal treatment for unexplained infertility: the fast track and standard treatment (FASTT) trial". Fertility and Sterility. 94 (3): 888–899. doi:10.1016/j.fertnstert.2009.04.022. ISSN 0015-0282. PMID 19531445.
- ^ Mladovsky, Philipa; Sorenson, Corinna (3 April 2009). "Public Financing of IVF: A Review of Policy Rationales". Health Care Analysis. 18 (2): 113–128. doi:10.1007/s10728-009-0114-3. ISSN 1065-3058. PMID 19343499.
- ^ Harrison BJ, Hilton TN, Rivière RN, Ferraro ZM, Deonandan R, Walker MC (16 August 2017). "Advanced maternal age: ethical and medical considerations for assisted reproductive technology". International Journal of Women's Health. 9: 561–570. doi:10.2147/IJWH.S139578. PMC 5566409. PMID 28860865.
- ^ Lung FW, Chiang TL, Lin SJ, Lee MC, Shu BC (April 2018). "Assisted reproductive technology has no association with autism spectrum disorders: The Taiwan Birth Cohort Study". Autism. 22 (3): 377–384. doi:10.1177/1362361317690492. PMID 29153004. S2CID 4921280.
- ^ Adashi EY, Rock JA, Rosenwaks Z (1996). Reproductive endocrinology, surgery, and technology. Philadelphia: Lippincott-Raven. pp. 1394–1410.
- ^ Sunderam S, Kissin DM, Zhang Y, Folger SG, Boulet SL, Warner L, et al. (April 2019). "Assisted Reproductive Technology Surveillance - United States, 2016". MMWR. Surveillance Summaries. 68 (4): 1–23. doi:10.15585/mmwr.ss6804a1. PMC 6493873. PMID 31022165.
- ^ Mastony C (21 June 2009). "Heartache of infertility shared on stage, screen". Chicago Tribune.
Reproductive technology
View on GrokipediaDefinition and Scope
Biological Foundations of Reproduction
Human sexual reproduction relies on the fusion of male and female gametes, a process shaped by evolutionary pressures to maximize genetic fitness and offspring survival. In males, spermatogenesis produces approximately 100-400 million sperm per ejaculate, with rigorous selection during epididymal transit and capacitation in the female tract eliminating defective gametes through motility and acrosome reaction requirements.[13] Females ovulate a single oocyte per cycle from a finite pool of about 400 viable eggs, enforcing high parental investment due to anisogamy—the disparity in gamete size and number that drives sexual dimorphism and mate competition.[14] Fertilization typically occurs in the ampulla of the fallopian tube, where a single sperm penetrates the oocyte's zona pellucida via enzymatic digestion, triggering cortical granule release to block polyspermy and initiate zygote formation.[13] These mechanisms filter unfit gametes, as only robust sperm capable of navigating cervical mucus, uterine contractions, and tubal transport succeed, reflecting natural selection for viability.[15] Post-fertilization, the zygote undergoes cleavage while transported to the uterus, forming a blastocyst that implants into the endometrium around days 6-10, a process contingent on synchronized hormonal signals like progesterone-mediated decidualization to support trophoblast invasion and placental development.[16] Implantation and subsequent gestation, lasting approximately 40 weeks in humans, serve as checkpoints for embryonic viability, with the placenta facilitating nutrient exchange and immune tolerance while maternal resources impose costs that favor genetically fit offspring.[14] Evolutionary adaptations, such as selective miscarriage of aneuploid embryos, further enforce quality control, as early pregnancy loss rates exceed 50% of conceptions, predominantly due to chromosomal abnormalities incompatible with development.[17] This gestational commitment underscores causal constraints on reproduction, linking parental investment to offspring prospects under natural conditions. Empirical data indicate peak natural fecundity of 20-25% per menstrual cycle for women aged 20-25, declining to 15% by age 35 due to diminished oocyte quality.[18] [19] Age-related fertility decline stems primarily from rising meiotic errors in oocytes, with aneuploidy rates increasing from about 20-47% in women under 35 to over 70-85% by age 40-42, reducing viable embryo formation.[17] [20] [21] These patterns reflect evolutionary trade-offs, where limited oocyte reserves accumulate damage over time, imposing selective pressures that prioritize reproductive success in prime years and contextualize interventions in cases of subfertility.[14]Scope of Reproductive Technologies
Reproductive technologies refer to medical interventions designed to address infertility or enable reproduction in circumstances where natural conception is impaired, primarily through procedures that manipulate human gametes, embryos, or zygotes to facilitate pregnancy. These are collectively termed assisted reproductive technologies (ART) by organizations such as the World Health Organization (WHO) and the American Society for Reproductive Medicine (ASRM), encompassing treatments where eggs, sperm, or embryos are handled outside the body, including in vitro fertilization (IVF) and related techniques.[22][23] The scope prioritizes empirically validated methods that directly assist conception, excluding preventive measures like contraception, which inhibit rather than promote reproduction and belong to a distinct domain of family planning.[2] ART addresses infertility, defined by the WHO as a failure to achieve pregnancy after 12 months of regular unprotected intercourse, affecting approximately 17% of individuals of reproductive age globally at some point in their lifetime. This prevalence stems from factors including age-related ovarian reserve decline, male factor issues such as low sperm quality, tubal blockages in females, and lifestyle contributors like obesity or smoking, with biological causation rooted in gamete viability and implantation challenges. Reproductive technologies thus target these pathologies by bypassing natural barriers, such as low gamete counts or failed fertilization, rather than altering underlying causes like endocrine disruptions. Since the first IVF birth in 1978, ART has resulted in an estimated 10 to 13 million live births worldwide, reflecting cumulative cycles exceeding tens of millions and demonstrating scalability in clinical settings.[22][24] While contraception is excluded from this scope as it prevents rather than assists reproduction, its widespread use has causally contributed to elevated infertility rates by enabling deferred childbearing, which biologically heightens risks due to diminished oocyte quality and quantity after age 35. Studies confirm that female fertility declines sharply with age, independent of contraceptive method discontinuation, with miscarriage and aneuploidy risks rising post-ponement. This distinction underscores reproductive technologies' remedial focus on existing deficits, not upstream behavioral or preventive choices, though empirical data link prolonged deferral—facilitated by reliable contraception—to increased reliance on ART.[25][26]Distinction from Natural Reproductive Processes
Reproductive technologies intervene in the reproductive process by isolating gametes, performing fertilization in vitro, and manipulating embryos outside the body, thereby circumventing multiple evolved biological mechanisms that filter for viability in natural conception. In spontaneous reproduction, spermatozoa undergo selection in the female reproductive tract, facing barriers such as cervical mucus, uterine environment, and sperm competition, which favor genetically and epigenetically robust gametes capable of zona pellucida penetration and oocyte activation.[27] Oocyte quality is similarly vetted through follicular development and ovulatory cues tied to maternal physiology, while early embryonic cleavage occurs in vivo, where molecular checkpoints prune non-viable zygotes before implantation. These safeguards, honed by natural selection, minimize propagation of deleterious mutations and imprinting errors, linking reproductive success to overall organismal fitness.[28] Assisted reproductive technologies (ART), such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), decouple these elements by harvesting gametes via hormonal stimulation and surgical retrieval, fertilizing in controlled media, and culturing embryos ex vivo before transfer. ICSI, for instance, directly injects a single spermatozoon into the oocyte, bypassing tract-based selection, zona binding, and acrosome reaction—processes that exclude suboptimal sperm in nature. In vitro culture alters epigenetic landscapes through exposure to non-physiological conditions, potentially disrupting genomic imprinting, as evidenced by elevated incidences of disorders like Beckwith-Wiedemann syndrome (OR up to 4-10 times higher) and Silver-Russell syndrome in ART-conceived children compared to spontaneous conceptions.[29] [30] This circumvention raises causal concerns about long-term developmental fitness, as lab-selected embryos may harbor latent instabilities not apparent in morphological assessments. Empirical data underscore these trade-offs: meta-analyses indicate ART confers a 22% higher relative risk of congenital anomalies (OR 1.22, 95% CI 1.17-1.28) even after adjusting for parental subfertility and confounders, with specific elevations in cardiovascular, musculoskeletal, and genitourinary defects. Multiple gestations, rarer in natural reproduction (twins ~1 in 80-90 pregnancies), surge in ART due to multi-embryo transfers—historically exceeding 30% twin rates in IVF cycles before single-embryo policies reduced them to ~10-15%—amplifying perinatal complications absent in singleton natural outcomes. Natural processes thus impose stricter viability thresholds, yielding lower baseline rates of epigenetic perturbations and multiples, whereas ART's interventions, while enabling conception, trade evolved robustness for procedural control.[31] [32] [33]Historical Development
Pre-Modern and Early Scientific Attempts
In 1677, Dutch microscopist Antonie van Leeuwenhoek first observed and described spermatozoa—termed "animalcules"—in human semen samples viewed through self-crafted microscopes with magnifications up to 270 times.[34] This empirical breakthrough shifted understandings of reproduction from purely humoral theories toward cellular mechanisms, though van Leeuwenhoek hypothesized that sperm contained preformed miniature organisms, underestimating the oocyte's role.[35] By the late 18th century, experiments confirmed sperm's causal necessity in fertilization. In 1779, Italian physiologist Lazzaro Spallanzani demonstrated that filtered semen lacking spermatozoa failed to produce offspring in animal trials, isolating sperm as the key male factor while highlighting environmental sensitivities like temperature and media that preserved viability.[36] Early artificial insemination attempts in animals, such as those by Spallanzani on dogs and frogs, yielded inconsistent results due to inadequate timing relative to ovulation and neglect of post-insemination transport dynamics in the female tract.[37] Human applications emerged amid these animal precedents but faced high failure rates from similar oversights. In 1884, Philadelphia physician William Pancoast conducted the first documented donor insemination, injecting semen from a selected medical student into an anesthetized infertile woman without her prior knowledge, resulting in a male birth nine months later.32127-1/abstract) Such procedures underscored causal gaps: success hinged on chance alignment of insemination with fertile windows, but absent precise oocyte-sperm synchronization or viability assays, outcomes remained empirically poor, with most attempts yielding no conception.[38] Animal models advanced modestly into the 19th century's end. In 1890, British embryologist Walter Heape performed the first successful mammalian embryo transfer, flushing fertilized ova from an Angora rabbit doe and implanting them into a Belgian hare surrogate, which delivered hybrid offspring.[39] This demonstrated embryo viability outside natural gestation but revealed non-translatability barriers, as rabbit-specific uterine synchrony and immunological tolerances did not generalize to primates or humans, where developmental timing and endometrial receptivity proved more stringent.[40] These pre-modern efforts collectively faltered on biological realism, prioritizing sperm isolation over integrated oocyte-sperm interactions and failing to replicate in vivo conditions like capacitation or zona pellucida penetration. By the early 20th century, sporadic insemination trials persisted with low efficacy—often below 10% in documented cases—until institutionalization spurred rigor. In 1944, the American Society for the Study of Sterility (predecessor to the ASRM) formed in Chicago under leaders like Walter Williams to systematize infertility research amid expanding clinical demands.[41]Mid-20th Century Foundations
In the 1950s, pivotal discoveries in mammalian reproductive biology established core principles for assisted reproduction. Min Chueh Chang and Colin Russell Austin independently identified sperm capacitation, a physiological maturation process occurring in the female reproductive tract that enables sperm to fertilize oocytes, overturning prior assumptions about immediate fertilizing ability.[42] This breakthrough facilitated the first successful in vitro fertilization (IVF) of rabbit oocytes by Chang in 1959, yielding live births after transfer, and extended to mouse models through embryo culture advancements by researchers like John McLaren and Daniel Biggers, who achieved blastocyst development in defined media.[43] These animal experiments demonstrated that oocytes could be fertilized externally and cultured briefly, providing empirical proof-of-concept for overcoming fertilization barriers, though human applications remained exploratory due to technical and ethical constraints.[44] Human tubal transfer experiments in the mid-1950s built on these foundations, attempting to mimic natural implantation by depositing fertilized or unfertilized gametes directly into the fallopian tubes. Early trials, often involving donor gametes, aimed to address tubal blockages or unexplained infertility but yielded inconsistent results, with no confirmed pregnancies until later refinements; these efforts highlighted the challenges of synchronizing gamete viability and tubal transport without advanced microscopy or media.[45] Concurrently, rising infertility diagnoses—estimated at 10-15% of couples in industrialized nations by the 1960s, partly attributable to urbanization-induced lifestyle shifts and delayed marriage reducing peak fertility windows—spurred demand for scalable interventions over behavioral adjustments like earlier family formation.[46][47] By the 1960s and 1970s, intrauterine insemination (IUI) emerged as a standardized procedure, involving semen washing to remove seminal plasma and prostaglandins followed by catheter deposition into the uterus, improving success over intracervical methods by circumventing mucus hostility and enhancing sperm concentration near the fertilization site.[46] Clinical protocols, refined in fertility centers, reported pregnancy rates of 5-10% per cycle for donor IUI, with fresh semen preferred until cryopreservation protocols matured. Ethical discussions intensified around donor anonymity, with practices enforcing secrecy via clinic agreements to safeguard donor-recipient separation and family integrity, though precursors to later rights-based critiques surfaced in medical literature questioning long-term psychological impacts on offspring.[48] These developments positioned IUI as a low-invasiveness bridge to more complex technologies, driven by causal realities of age-related oocyte decline rather than solely pathological factors.[46]Post-1978 IVF Revolution and Milestones
The advent of in vitro fertilization (IVF) culminated in the birth of Louise Brown on July 25, 1978, in Oldham, United Kingdom, the first human conceived via retrieval of oocytes, fertilization with spermatozoa in a laboratory dish, and subsequent embryo transfer to the uterus.[49] This milestone, achieved by gynecologist Patrick Steptoe and physiologist Robert Edwards after over a decade of experimentation, demonstrated the feasibility of bypassing tubal factors in infertility but yielded initial live birth rates below 10% per initiated cycle due to inefficiencies in oocyte retrieval, embryo culture, and implantation.[50][49] Refinements in the 1980s expanded IVF applicability, with controlled ovarian hyperstimulation protocols improving oocyte yield and blastocyst culture extending embryo development for better selection.[49] A pivotal 1992 innovation, intracytoplasmic sperm injection (ICSI), addressed severe male-factor infertility by injecting a single spermatozoon directly into the oocyte cytoplasm, dramatically increasing fertilization rates from under 20% in conventional insemination to over 70% in ICSI cases and accounting for approximately 60% of global IVF cycles by the early 2000s.[51] The 1990s introduced preimplantation genetic testing (PGT), first applied in 1990 to screen embryos for sex-linked disorders like hemophilia, enabling selection of unaffected ones and reducing transmission risks; by the decade's end, polymerase chain reaction and fluorescence in situ hybridization techniques expanded PGT to aneuploidy detection, though with limitations in accuracy for monogenic conditions.[49] Cryopreservation advanced in the 2000s via vitrification—a rapid freezing method using cryoprotectants—which supplanted slow-freezing protocols, boosting post-thaw embryo survival from 60-70% to over 90% and enabling deferred transfers that contributed to cumulative live birth rates approaching 50% across multiple cycles for women under 35.[51] By the 2010s, global assisted reproductive technology (ART) had resulted in over 5 million cumulative births, with success rates per fresh cycle rising to 30-40% for younger patients through integrated advancements like extended embryo culture and single embryo transfer to minimize multiples.[52][49] Into the 2020s, adjuncts such as time-lapse imaging for non-invasive embryo assessment and algorithmic predictions of implantation potential further refined selection, yet per-cycle efficacy remained below peak natural fecundity rates of 20-25% observed in young fertile couples, underscoring ongoing biological constraints in replicating endogenous signaling and endometrial receptivity.[53][49] Worldwide, ART births exceeded 10 million by 2023, reflecting scaled adoption amid these incremental gains.[24]Core Technologies and Methods
Gamete and Embryo Manipulation Techniques
Gamete manipulation begins with oocyte retrieval, typically performed via transvaginal ultrasound-guided aspiration 35-36 hours after human chorionic gonadotropin administration to collect mature oocytes from ovarian follicles.[54] Retrieved oocytes are then denuded of surrounding cumulus cells using enzymatic and mechanical methods to facilitate assessment and preparation for fertilization.[55] Sperm processing involves techniques such as density gradient centrifugation or swim-up to isolate motile, morphologically normal spermatozoa from semen, reducing exposure to seminal plasma and potential contaminants.[56] These methods aim to select sperm with higher DNA integrity, though advanced selections like magnetic-activated cell sorting target specific biomarkers for improved quality.[57] Intracytoplasmic sperm injection (ICSI) represents a key gamete manipulation where a single spermatozoon is microinjected directly into the oocyte cytoplasm, bypassing natural barriers; it is employed in approximately 70% of IVF cycles worldwide, including many without severe male factor infertility.[58] Embryo manipulation includes extended in vitro culture to the blastocyst stage under optimized media and atmospheric conditions approximating the fallopian tube microenvironment, such as low oxygen tension (5%) and sequential nutrient formulations.[59] However, such culture conditions can lead to altered gene expression profiles compared to in vivo development, with upregulated genes related to stress response and metabolism observed in vitro embryos.[60] Preimplantation genetic testing (PGT) requires embryo biopsy, preferentially of 5-10 trophectoderm cells from day 5-6 blastocysts using laser-assisted hatching to minimize impact on the inner cell mass, followed by genetic analysis for aneuploidy, monogenic disorders, or structural variants.[61] This technique enables selection of euploid embryos but introduces potential risks from cell removal and in vitro handling.[62]Assisted Fertilization Procedures
Assisted fertilization procedures encompass techniques such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), which facilitate gamete fusion outside the body to address infertility, particularly female factors like ovulatory dysfunction and age-related oocyte aneuploidy that contribute to roughly 37% of cases solely and an additional 35% when combined with male factors.[63] In a standard IVF cycle, ovarian stimulation begins with gonadotropin injections over 8-14 days to recruit multiple follicles, monitored via ultrasound and estradiol levels, followed by human chorionic gonadotropin (hCG) trigger for final maturation.[64] Egg retrieval occurs 34-36 hours post-trigger via transvaginal aspiration under ultrasound guidance and sedation, yielding 10-15 oocytes on average.[64] Fertilization proceeds by combining retrieved oocytes with prepared sperm in culture medium, allowing natural penetration for conventional insemination, or via ICSI where a single motile sperm is microinjected directly into the oocyte cytoplasm using a micropipette under microscopic guidance, primarily for severe male factor issues like low sperm count or motility.[65] Fertilized oocytes, identified by pronuclei formation 16-18 hours later, undergo culture for 3-5 days to cleavage or blastocyst stages before selection for transfer.[64] Embryo transfer involves catheter placement through the cervix to deposit 1-2 embryos into the uterine cavity, guided by ultrasound in modern protocols.[66] Variants include frozen embryo transfer (FET), where surplus or all embryos are vitrified post-fertilization and thawed for transfer in a subsequent cycle after endometrial preparation with estrogen and progesterone to optimize receptivity and avoid supraphysiologic hormone effects from stimulation.[67] By 2020, FET constituted over 75% of U.S. treatment cycles, reflecting shifts toward elective single-embryo transfer and improved synchronization. These procedures integrate with gamete donation, using donor oocytes or sperm in place of patient gametes during stimulation/retrieval or insemination phases, and surrogacy, where transfer occurs into a gestational carrier's uterus post-IVF.[64]Cryopreservation and Storage Methods
Cryopreservation techniques in reproductive technology primarily involve two methods: slow freezing, which gradually cools gametes or embryos to avoid ice crystal formation, and vitrification, a rapid cooling process that achieves a glass-like solidification state. Slow freezing, developed in the 1980s for embryos, exposes cells to cryoprotectants and controlled dehydration before cooling at rates of about 0.3–2°C per minute, but it yields oocyte survival rates of 65–90%.[68] Vitrification, introduced for human oocytes in the late 1990s with the first live birth reported in 1998 from an immature oocyte and refined for mature oocytes by the early 2000s, uses high concentrations of cryoprotectants and ultra-rapid cooling (up to 23,000°C per minute) via direct immersion in liquid nitrogen, achieving survival rates of 84–99% for oocytes and over 95% for embryos.[69][70] This shift to vitrification as the standard method since the mid-2000s has minimized intracellular ice formation, a primary cause of cellular damage in slow freezing.[71] For oocytes, vitrification protocols involve equilibrating cells in stepwise cryoprotectant solutions (e.g., ethylene glycol and dimethyl sulfoxide) before loading into carrier devices like straws or cryotops and plunging into liquid nitrogen at -196°C. Sperm cryopreservation, routinely practiced since the 1950s, typically employs slow freezing with glycerol as a protectant, though vitrification adaptations have emerged for improved post-thaw motility in some species; human sperm storage remains effective long-term with minimal viability loss over decades.[72] Embryos at cleavage or blastocyst stages are vitrified similarly, with survival exceeding 98% in optimized labs, enabling storage durations of 10–15 years or more without significant degradation when maintained in vapor-phase liquid nitrogen tanks.[73] These methods decouple ovarian stimulation from embryo transfer, reducing the need for synchronized fresh cycles and allowing multiple transfers from a single stimulation.[74] The adoption of oocyte vitrification surged in the 2010s, driven by fertility preservation for medical and elective reasons, with clinics reporting thousands of procedures annually by 2015. However, live birth rates per thawed oocyte remain low, averaging 2.75–5% depending on age at freezing and number thawed, as fertilization and implantation efficiencies post-thaw hover around 70–80%.[75][76] Storage challenges include maintaining stable cryogenic conditions to prevent temperature fluctuations, which can cause devitrification and cell lysis, necessitating robust monitoring systems in IVF labs.[72] Biological preservation hurdles persist, as cryopreservation induces osmotic and thermal stresses that can lead to DNA strand breaks in gametes and embryos, primarily via oxidative stress and abortive apoptosis rather than ice crystals in vitrification. Studies document increased DNA fragmentation indices in post-thaw sperm (up to 20–30% higher than fresh) and oocytes, though embryo development competence is often preserved due to maternal DNA repair mechanisms.[77][78] These cryo-induced damages underscore the need for protocol optimizations, such as antioxidant supplementation, to enhance molecular integrity without compromising efficiency gains.[79]Clinical Outcomes and Biological Risks
Success Rates and Prognostic Factors
Success rates in assisted reproductive technology (ART), primarily measured as live birth rates per initiated cycle or embryo transfer using autologous oocytes, vary significantly and are generally lower than natural fecundity rates for women of comparable ages attempting conception without intervention.[7] Nationally, approximately 37.5% of ART cycles initiated in 2022 resulted in a live birth, reflecting data from over 400,000 cycles reported to the CDC.[7] This overall figure masks substantial age-related declines, as maternal age at oocyte retrieval is the dominant prognostic factor, driven by progressive deterioration in oocyte quantity and quality, including increased aneuploidy and mitochondrial dysfunction.[80][81]| Maternal Age Group | Live Birth Rate per Cycle (Autologous Oocytes) |
|---|---|
| <35 years | 40-55% |
| 35-37 years | ~36% |
| 38-40 years | ~23-27% |
| 41-42 years | ~12-15% |
| >42 years | <5-10% |
