Large for gestational age describes full-term or post-term infants that are born of high birth weight. The term LGA or large for gestational age is defined by birth weight above the 90th percentile for their gestational age and gender. In infants with birth weight above the 97th percentile in their gestational age and gender group, research has shown that greater risk of long-term health complications and fatal outcomes are present in LGA infants. Specifically, large for gestational age can be characterized by macrosomia, referring to a fetal growth beyond a certain threshold. Experts in Obstetrics and Gynecology currently use a grading system to evaluate LGA infants, where their birth weight may help identify risks associated with their birth, including labor complications of both mother and child, potential long-term health complications of the neonate and infant mortality.
Complications
Common risks in LGA babies include shoulder dystocia, hypoglycemia, metatarsus adductus, hip subluxation and talipes calcaneovalgus due to intrauterine deformation. Macrosomic neonates are at a higher risk of being overweight and obese than their normal-weight counterparts later in life. Shoulder dystocia can result from the anterior shoulder becoming impacted on the maternal symphysis pubis. The doctor or midwife will try to push the baby's anterior shoulder downward to pass through the birth canal and clear the woman's symphysis pubis. This can be difficult if the child is LGA, since the birth canal is 10 cm when fully dilated for most women and there may not be much room to move the baby. If shoulder dystocia occurs, there are various manoeuvres which can be performed by the birth attendant to try to deliver the shoulders. These generally involve trying to turn the shoulders into the oblique, using suprapubic pressure to disimpact the anterior shoulder from above the symphysis pubis, or delivering the posterior arm first. If these do not resolve the situation, the provider may intentionally snap the baby's clavicle in a procedure called cleidotomy in order to displace the shoulder and allow the child to be delivered. The bone should heal spontaneously, and most babies will make a full recovery from this birth injury. There is still a risk of temporary or permanent nerve damage to the baby's arm, or other injuries such as humeral fracture. Although big 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 big babies. Researchers have found that it is not possible 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, 6.7% of the time in babies that weigh to, and 14.5% of the time in babies that weigh more than. Big babies are at higher risk of hypoglycemia in the neonatal period, independent of whether the mother has diabetes.
Risk factors
One of the primary risk factors of LGA is poorly-controlled maternal diabetes, particularly gestational diabetes, as well as preexisting diabetes mellitus . This increases maternal plasma glucose levels as well as insulin, stimulating fetal growth of subcutaneous fat. The LGA newborn exposed to maternal DM usually only has an increase in weight, not a change in body length or head size.
Genetics
Genetics plays a role in having a baby born with LGA. Taller, heavier parents tend to have larger babies. Genetic disorders of overgrowth are often characterized by macrosomia.
Others
Gestational age: pregnancies that go beyond 40 weeks increase incidence of an LGA infant
Fetal sex: male infants tend to weigh more than female infants
Obesity prior to pregnancy and excessive maternal weight gain during pregnancy.
Diagnosing fetal macrosomia cannot be performed until after birth, as evaluating a baby's weight in the womb may be inaccurate. While ultrasound has been the primary method for diagnosing LGA, this form of fetal weight assessment remains to be imprecise, as the fetus is a highly variable structure in regards to density and weight— no matter the gestational age. Ultrasonography involves an algorithm that incorporates biometric measurements of the fetus, such as biparietal diameter, head circumference, abdominal circumference, and femur length, to calculate the estimated fetal weight. 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 born to only 1 out of 10 women, the 2013 Listening to Mothers Survey found that 1 out of 3 American women were told that their babies were too big. The average birth weight of these suspected “big babies” was only. Care provider concerns about a suspected big baby were the fourth-most common reason for an induction, and the fifth-most common reason for a C-section. This treatment is not based on current best evidence. Research has consistently shown that, as far as birth complications are concerned, the care provider’s perception that a baby is big is more harmful than an actual big baby by itself.
Treatment
Induction of labor for women with a baby with suspected macrosomia leads to babies being born at a lower birth weight, with fewer bone fractures and less shoulder dystocia, but could increase the number of women with perineal tears. Predicting a baby’s weight can be inaccurate and women could be worried unnecessarily, and request their labor to be induced for no reason. Doctors disagree whether women should be induced for suspected macrosomia and more research is needed to find out what this is best for women and their babies.
