Large for gestational age (LGA) babies are those whose birth weight lies above the 90th percentile for that gestational age. Macrosomia, also known as big baby syndrome, is sometimes used synonymously with LGA, or is otherwise defined as a fetus that weighs above 4000 grams (8 lb 13 oz) or 4500 grams (9 lb 15 oz) regardless of gestational age.

Diagnosis

LGA is generally not diagnosed until after the birth, as the size and weight of the child is rarely checked during the latter stages of pregnancy. Babies that are large for gestational age throughout the pregnancy can sometimes be seen during a routine ultrasound, although fetal weight estimations late in pregnancy are quite imprecise.

There are believed to be links with polyhydramnios (excessive amniotic sac fluid).

Predetermining factors

One of the primary risk factors is poorly-controlled diabetes, particularly gestational diabetes (GD), as well as preexisting diabetes mellitus (DM). This increases maternal plasma glucose levels as well as insulin, stimulating fetal growth. The LGA newborn exposed to maternal DM usually has an increase only in weight. LGA newborns that have complications other than exposure to maternal DM present with universal measurements >90th percentile.

Other indicating factors include:

• Gestational age; pregnancies that go beyond 40 weeks increase incidence
• Fetal sex; male infants tend to weigh more than female infants
• Genetic factors; taller, heavier parents tend to have larger babies, with an obese mother greatly increasing the chances
• Excessive maternal weight gain
• Maternal Diabetes
• Multiparity (have 2-3x the number of LGA infants vs. primaparas)
• Congenital anomalies (transposition of great vessels) - Hydrops Fetalis
• Erythroblastosis fetalis - Hydrops Fetalis
• Use of some antibiotics (amoxicillin, pivampicillin) during pregnancy - Hydrops Fetalis

The condition is most common in mothers of African origin, partly due to the higher incidence of diabetes.

Treatment

Depending upon the relative size of the head of the baby and the pelvic diameter of the mother vaginal birth may become complicated. One of the most common complications is shoulder dystocia. Such pregnancies often end in caesarean sections in order to safely deliver the baby and to avoid birth canal lacerations. Upon birth, early feeding is essential to prevent fetal hypoglycemia. Early diagnosis of individual problems is required.

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