Large for gestational age

Large for gestational age
Specialty	Pediatrics

Large for gestational age (LGA) is an indication of high prenatal growth rate. LGA is often defined as a weight, length, or head circumference that lies above the 90th percentile for that gestational age. However, it has been suggested that the definition be restricted to infants with birth weights greater than the 97th percentile (2 standard deviations above the mean) as this more accurately describes infants who are at greatest risk for perinatal morbidity and mortality. Macrosomia, which literally means "big body," is sometimes confused with LGA. Some experts consider a baby to be big when it weighs more than 4,000 grams (8 pounds 13 ounces) at birth, and others say a baby is big if it weighs more than 4,500 grams (9 pounds, 15 ounces). A baby is also called “large for gestational age” if its weight is greater than the 90th percentile at birth

Diagnosis

It's important to note that LGA and macrosomia cannot be diagnosed until after birth, as it is impossible to accurately estimate the size and weight of a child in the womb. Babies that are large for gestational age throughout the pregnancy may be suspected because of an ultrasound, but fetal weight estimations in pregnancy are quite imprecise. For non-diabetic women, ultrasounds and care providers are equally inaccurate at predicting whether or not a baby will be big. If an ultrasound or a care provider predicts a big baby, they will be wrong half the time .

Although big babies are only born to 1 out of 10 women, the 2013 Listening to Mothers Surveyfound that 1 out of 3 American women were told that their babies were too big. In the end, the average birth weight of these suspected “big babies” was only 7 lbs 13 oz . In the end, care provider concerns about a suspected big baby were the 4th most common reason for an induction (16% of all inductions), and the 5th most common reason for a C-section (9% of all C-sections). Unfortunately, this treatment is not based on current best evidence .

In fact, research has consistently shown that the care provider’s perception that a baby is big is more harmful than an actual big baby by itself. In a very important 2008 study, researchers compared what happened to women who were suspected of having a big baby (>8 lbs 13 oz) to what happened to women who were not suspected of having a big baby—but who ended up having one (). In the end, women who were suspected of having a big baby (and actually ended up having one) had a triple in the induction rate; more than triple the C-section rate, and a quadrupling of the maternal complication rate, compared to women who were not suspected of having a big baby but who had one anyway.

Complications were most often due to C-sections and included bleeding (hemorrhage), wound infection, wound separation, fever, and need for antibiotics. There were no differences in shoulder dystocia between the 2 groups. In other words, when a care provider “suspected” a big baby (as compared to not knowing the baby was going to be big), this tripled the C-section rates and made mothers more likely to experience complications, without improving the health of babies ().

Predetermining factors

One of the primary risk factors of LGA is poorly-controlled diabetes, particularly gestational diabetes (GD), as well as preexisting diabetes mellitus (DM) (preexisting type 2 is associated more with macrosomia, while preexisting type 1 can be associated with microsomia). This increases maternal plasma glucose levels as well as insulin, stimulating fetal growth. The LGA newborn exposed to maternal DM usually only has an increase in weight. LGA newborns that have complications other than exposure to maternal DM present with universal measurements >90th percentile.

Genetics

Genetics plays a role in having a baby born with LGA. Taller, heavier parents tend to have larger babies. Babies born to an obese mother greatly increasing the chances.

Other Determining Factors

• Gestational age; pregnancies that go beyond 40 weeks increase incidence
• Fetal sex; male infants tend to weigh more than female infants
• Excessive maternal weight gain
• 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
• Genetic disorders of overgrowth (e.g. Beckwith-Wiedemann syndrome, Sotos syndrome)

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

Treatment

Big babies are at higher risk for temporarily getting their shoulders stuck [shoulder dystocia (“dis toh shah”)], but difficulty giving birth to shoulders is unpredictable and permanent injuries are rare.

Although big babies are at higher risk for shoulder dystocia, most cases of shoulder dystocia happen in smaller babies (). This is because there are many more small and normal size babies being born than big babies. Unfortunately, researchers have found that it is impossible to predict who will have shoulder dystocia and who will not ().

In non-diabetic women, shoulder dystocia happens 0.65% of the time in babies that weigh less than 8 lbs 13 oz (6.5 cases out of 1,000 births), 6.7% of the time in babies that weigh between 8 lbs 13 oz and 9 lbs 15 oz (60 out of 1,000), and 14.5% of the time in babies that weigh 9 lbs 15 oz or greater (145 out of 1,000) ().