Large for gestational age

Large for gestational age (LGA) is a term used to describe infants that are born with an abnormally high weight, specifically in the 90th percentile or above, compared to other babies of the same developmental age. Macrosomia is a similar term that describes excessive birth weight, but refers to an absolute measurement, regardless of gestational age. Typically the threshold for diagnosing macrosomia is a body weight between 4,000 and 4,500 grams (8 lb 13 oz and 9 lb 15 oz), or more, measured at birth, but there are difficulties reaching a universal agreement of this definition.

Evaluating an infant for macrosomia or LGA can help identify risks associated with their birth, including labor complications of both the parent and the child, potential long-term health complications of the child, and infant mortality.

Fetal macrosomia and LGA often do not present with noticeable patient symptoms. Important signs include large fundal height (uterus size) and excessive amniotic fluid (polyhydramnios). Fundal height can be measured from the top of the uterus to the pubic bone and indicates that the newborn is likely large in volume. Excessive amniotic fluid indicates that the fetus's urine output is larger than expected, indicating a larger baby than normal; some symptoms of excessive amniotic fluid include

LGA or macrosomic births can lead to complications for both the mother and the infant.

Common risks in LGA babies include shoulder dystocia, low levels of blood sugar, brachial plexus injuries, metatarsus adductus, hip subluxation and talipes calcaneovalgus, due to intrauterine deformation.

Shoulder dystocia occurs when the infant's shoulder becomes impacted on the mother's pubic symphysis during birth. Newborns with shoulder dystocia are at risk of temporary or permanent nerve damage to the baby's arm, or other injuries such as fracture. Both increased birth weight and diabetes in the gestational parent are independent risk factors seen to increase risk of shoulder dystocia. In non-diabetic women, shoulder dystocia happens 0.65% of the time in babies that weigh less than 8 pounds 13 ounces (4,000 g), 6.7% of the time in babies that weigh 8 pounds (3,600 g) to 9 pounds 15 ounces (4,500 g), and 14.5% of the time in babies that weigh more than 9 pounds 15 ounces (4,500 g). In diabetic women, shoulder dystocia happens 2.2% of the time in babies that weigh less than 8 pounds 13 ounces (4,000 g), 13.9% of the time in babies that weigh 8 pounds (3,600 g) to 9 pounds 15 ounces (4,500 g), and 52.5% of the time in babies that weigh more than 9 pounds 15 ounces (4,500 g). Although larger babies are at higher risk for shoulder dystocia, most cases of shoulder dystocia happen in smaller babies because there are many more small and normal-size babies being born than large babies.

LGA babies are at higher risk of low blood sugar (hypoglycemia) in the neonatal period, independent of whether the mother has diabetes. Hypoglycemia, as well as hyperbilirubinemia and polycythemia, occurs as a result of hyperinsulinemia in the fetus.

High birth weight may also impact the baby in the long term, as studies have shown associations with increased risk of overweight, obesity, and type 2 diabetes mellitus. Studies have shown that the long-term overweight risk is doubled when the birth weight is greater than 4,000 g. The risk of type 2 diabetes mellitus as an adult is 19% higher in babies weighing more than 4,500 g at birth compared to those with birth weights between 4,000 g and 4,500 g.