Fetal EEG

Fetal electroencephalography, also known as prenatal EEG includes any recording of electrical fluctuations arising from the brain of a fetus.  Doctors and scientists use EEGs to detect and characterize brain activity, such as sleep states, potential seizures, or levels of a coma. EEG captures the electrical activity in the vicinity of the recording electrodes. The majority of the neural electrical activity arises from the flow of current from the cell bodies of pyramidal neurons to their apical dendrites, which become depolarized by excitatory inputs from other neurons. To record the most accurate signals, scientists try to minimize the distance between the recording electrode and the neural activity that they want to detect. Given the difficulty of attaching electrodes to a fetus inside a uterus, doctors and scientists use a variety of techniques to record fetal brain activity.

The three most common techniques for recording electrical brain activity before birth include:

The recording of the youngest fetus was performed between 43 and 45 days gestation and revealed some EEG features observed in newborns.

In 1942, Dr. Lindsley recorded the first electrical activity from the brain of an unborn infant when he noticed that an electrical recording from his pregnant wife's lower abdomen resembled the electrical recordings from the scalp of a newborn. To follow up, in 1955, Bernstine, Borkowski and Price examined and described 32 fetal EEGs recorded from the maternal abdomen and cervix during labor. However, since scientists could not affix the electrodes to the fetus's scalp, continuous recordings were difficult to obtain. With the invention of suction cup electrodes, doctors could get continuous recordings from the same brain location during labor and delivery. From 1955 to 1976, many scientific groups made EEG recordings from electrodes placed on the maternal abdomen, or placed on the cervix using a speculum, and techniques continued improving.

In the 1980s, functional MRI or magnetoencephalography became the primary research tools for the prenatal study of human brain development; however, fetal EEG prevailed in clinical settings for determining sleep states in the unborn, or fetal distress.

Healthy newborns display two patterns of electrical activity described as "discontinuous" and "trace alternant" activity. "Discontinuous" electrical activity describes sharp bursts of electrical activity followed by low frequency waves; "trace alternant" electrical activity describes sharp bursts followed by short high amplitude intervals. Trace alternant activity has been correlated with quiet sleep. In the third trimester, normally developing fetuses show discontinuous and trace alternant patterns resembling those measured from normal newborns. Interestingly, as preterm infants advance in gestational age, the more likely they are to display low frequency waves and trace alternant activity; discontinuous activity becomes more rare the older a preterm infant is born.

Between 1955 and 1961, Winslow Borkowski and Richard Bernstine, doctors at Jefferson Medical College Hospital, temporarily preserved tiny unborn fetuses removed during ectopic pregnancies and recorded from their brains. The team used needle electrodes to record brain activity at 3 millimeters and 1 centimeter below the brain surface. These electrodes penetrated the cranial tissue, which solves the problem of electrical interference from nearby muscles.

The youngest fetus that Borkowski and Bernstine studied was between 43 and 45 days post-conception – only 16mm long. At 45 days after conception, the brain is bent forward and is almost as large as the entire body of the fetus, allowing for these deep recordings. The 45-day-old fetus's electrical signals resembled the "discontinuous" patterns observed in healthy newborns, premature infants, and fetuses in the last trimester of pregnancy. The doctors also observed patterns that resembled "sleep spindles" in adults. The scientists continued recording until they consistently observed patterns of brain death, since the fetuses could not survive outside the uterus.