Great Expectations: What Happens when Your Baby Is Big

Big Baby

It seems that as long as we’ve been seeing ads on television, we’ve had constant introductions to products that claim to make our children grow up “big and strong.”  While that might be an admirable goal for a growing child, it can be a less desirable outcome for a fetus and newborn baby.

The fact is that when it comes to birth, size can and does matter, and not always in a good way.  A large-sized fetus or newborn is said to have macrosomia, and the baby or baby-to-be does face some risks associated with its size.

In the past, we’ve talked some about macrosomia as well as one of its more common causes.  Let’s look a little more about when obstetricians and pediatricians might be concerned and some things they might think about doing to increase the chances of a healthy Mom and baby.

Define “Big”

Most physicians define a macrosomic newborn as one over 4000 grams, or 8 pounds 13 ounces.  That definition won’t work for premature infants, who are expected to be smaller.  Thus, you might hear someone refer to a macrosomic baby as “large for gestational age”—usually over the 90thpercentile for what newborns generally run, weight-wise, based on their due date.

Your obstetrician will assess the fetus for size at the time of your ultrasound.  Unfortunately, this has turned out to be a very inexact science:  there are many different formulas used for weight estimation, and there doesn’t appear to be one that’s superior.  Some studies have even found that a mother’s estimation of weight was as accurate as an ultrasound or clinical examination!  The jury appears to be out on the best approach—perhaps it lies with serial ultrasounds, or a combination of ultrasound and other statistics (such as mother’s weight gain during pregnancy).

But What Does It All Mean?

And why should we be concerned?  If you’re a Mom who has delivered a large baby, you may already have had a chat with your obstetrician about potential complications to women who undergo delivery of a macrosomic infant, particularly vaginally.  That said, many women are able to have a vaginal delivery, particularly in the lower macrosomic weight ranges.

Your newborn doctor, however, may have additional concerns, and they fall into two categories.  First, there are issues associated simply with being big and being born, such as shoulder injury.  This can happen due to shoulder dystocia, a term used to describe the shoulders getting stuck during delivery.  While most shoulder injuries are temporary and get better with a minimum of extra care, your baby’s provider would need to monitor your new arrival closely for improvement.

But in addition to looking for problems associated with the delivery of a large baby, your pediatrician would be concerned with what caused her to be Ms. Big in the first place.  Although it is sometimes just the luck of the draw, certain factors are associated with large babies:  family history, being born past due date, being of Hispanic or African American ancestry, being an older Mom or one with many previous pregnanciesObese mothers also tend to have bigger babies.

However, your newborn’s doctor would be especially concerned if you have diabetes, whether as a chronic illness or only during pregnancy (“gestational”).  Diabetes, especially if poorly controlled, can cause other baby problems in addition to large size.

Your pediatrician might also be concerned about the possibility of one of the many genetic syndromes.  Although these are much rarer, these are inherited abnormities which usually affect several of the infant’s body systems.  The physician might look more closely for this if baby is very large, if none of the above explanations for his size apply, or if something else unusual is noted on ultrasound.

And…What Happens Now?

Many mothers-to-be may wonder if there is something they can do to prevent having a larger-than-normal baby.  Certainly obese and diabetic woman should pay close attention to diet and take any prescribed medications under the supervision of their obstetrician.  (If you’re obese and planning a child, it’s most helpful to try and lose weight prior to conception.)  However, if the baby’s big and those issues don’t apply, there are generally no extra home measures for Mom.

However, your obstetric and pediatric providers are vested in making the delivery and the newborn period go well for both Mom and baby.  For this reason, they will follow pregnancies complicated by fetal macrosomia a little more closely.  The obstetrician will help manage weight and diabetes, if present, and may decide to deliver the baby early or by cesarean section.  Each baby, as well as each obstetrician, is different on these points, and it’s a good idea for the two of you to have a discussion about any concerns you may have.  If the baby is delivered vaginally, sometimes Mom and baby can be manipulated during delivery to minimize the risk of complications.

Once born, the pediatric provider will monitor the baby closely.  He’ll look for equal movement of the arms and intact clavicles (collarbones).  He will also make sure there are no obvious signs of a genetic syndrome and that the baby is breathing well.  Finally, all big babies—not just those where Mom has diabetes—are watched carefully for low blood sugar.

You can’t always control or influence the chances of having one with macrosomia.  But with good, regular prenatal care and (when needed) attention to your provider’s instructions on managing your weight, you can reduce the risks of the condition for yourself and your baby.

Stan Sack
Dr. Stan Sack has 29 years’ experience as a primary care pediatrician in Massachusetts and Florida. A medical writer since 2015, he enjoys blogging on topics that are on parents’ minds but are covered less often in books and on websites. He lives in the Florida Keys with his family and enjoys healthy cooking, fitness activities and singing in his spare time.

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