Macrosomia is the term used to define an infant that measures more than 8 pounds 13 ounces or 4,000 grams (4 kg) at birth. Some definitions use 4,5000 grams (9lb 15oz) as cutoff. While macrosomia can be suspected prior to birth mostly from ultrasound measurements, it is only definitively determined after birth by weighing the baby. Ultrasound measurements to calculate the baby's weight are not always accurate. No matter how many ultrasounds measure high birth weight, the condition is only definitively determined after birth. When all factors are taken into consideration, macrosomia affects on average about 10-pecent of births. In rare cases macrosomia is measured in premature infants, but most often the high birth weight is associated with gestational diabetes or other medical factors affecting the pregnancy. Male infants tend to weigh more than female infants, so macrosomia may affect boys more often than girls. 

Why does the baby have macrosomia?

Many times, the exact cause of the macrosomia is unknow. There are certain conditions such as maternal diabetes that increase the risk of macrosomia. Other causes may include the parents' genetics which occasionally increases the risk of macrosomia. Postdate pregnancies are also more like to lead to babies with macrosomia. 

Hospital Care of an Infant with Macrosomia

Being born weighing more than 8 pounds 13 ounces does not always constitute a medical problem. Later gestation, beyond the 40th week, can cause increased birth weight. Gestational diabetes can also affect birth weight, but gestational diabetes affects the pregnant woman not the infant. Most medical considerations regarding macrosomia affect pregnancy and birth and not the infant after birth. For instance, infants that weigh more are at a higher risk of C-section delivery. C-section delivery increases the risk of infant and birth morbidity.

Hospital care for the infant with expected macrosomia is of greater concern than after-birth care, in some cases. Hospitals and obstetricians work together to prevent birth complications like shoulder dystocia and other birth injuries. Death during birth due to complications associated with fetal size can also be a concern in extreme cases, so care for the infant with macrosomia often starts during delivery and continues after birth. After the infant is born, nurses and doctors will watch blood glucose and electrolyte balance carefully. Infants with macrosomia may have trouble maintaining healthy glucose and electrolyte levels immediately after birth.

Preventing Macrosomia

Not all cases of macrosomia have a known cause, but having an infant with macrosomia increases the risk of the condition happening again in future pregnancies. Mothers with gestational diabetes may be placed on a special diet to reduce the impact on the fetus and keep weight within normal limits. If the obstetrician notices excessive weight gain during pregnancy, diet alterations may also be suggested as prenatal weight gain is associated with increased risk of macrosomia. 

If there is no known cause of macrosomia, obstetricians may schedule C-sections for future pregnancies to prevent uterine dehiscence. Dehiscence is the spontaneous opening of the uterus due to pressure on a previous C-section scar or due to thinning of the uterus caused by excessive fetal weight and size.