Congratulations Mama! You have made it into the final trimester of pregnancy. You have passed nausea filled mornings (hopefully!) and the stress of when to tell coworkers and family, you’ve made it far! It is completely normal to start worrying about the details of delivery. It is more than normal to worry about the size of your baby- especially if you are delivering naturally. You’re not the only one on your birthing team thinking about your baby in terms of size. Your doctors try to determine your baby’s weight as accurately as possible so they can plan the best birthing plan beforehand. However, it is extremely difficult to predict the correct weight. The medical term for a large baby is macrosomia.
In a recent study, one-third of women reported their OB provider told them their baby might be getting “quite large” near the end of pregnancy. In the end, however, only one in five of those women had a baby that weighed more than 8 pounds, 13 ounces or 4000 grams, a common threshold for labeling a baby “large.” About 8 percent of the nation’s deliveries involve babies with macrosomia, according to the American College of Obstetricians and Gynecologists. But only 1 percent of newborns weigh 9 pounds, 9 ounces or more.
The threshold for what is considered a ‘big baby‘ is hard to calculate. Usually, in order for a baby to be considered large, he or she would have to weigh more than 10 pounds or 4500 grams. However, the real question is entirely objective, we really want to know if your baby is too big for your pelvis.
There are three parts to how doctors assess if your baby can be delivered vaginally, they’re called: the power, the passenger, and the passage.
The power is the actual force of contractions and can only be measured once labor begins. The passenger refers to the size of your baby. Weight and position in birth canal both make a big difference, as well as the direction your baby’s head is facing while descending in the canal. The passage refers to your pelvis, how narrow it is, how short it is, and ultimately if your baby can fit through comfortably.
While it is difficult to predict who will have a large baby, certain health factors play a role. Mothers with diabetes (including gestational) are a concern. High glucose levels can cross the placenta and lead to high levels in the fetus. As a response to these high sugar levels, the fetus produces insulin, which stimulates its own growth. In addition to diabetes, maternal obesity is another large indicator. The rate of macrosomia has increased over time with rising obesity rates, so we expect to actually see more macrocosmic babies in the future.
The main concerns for having a big baby are twofold. There are risks for the mother and separate risks for the baby. The most serious risk of fetal macrosomia is birth trauma for the baby, especially something called shoulder dystocia, where after the baby’s head is delivered the rest of his or her body does not deliver easily. Additionally, if the mother has high blood sugar the baby must be monitored closely for several hours because he or she is used to releasing more insulin because of the mother’s sugar. When the doctor cuts the cord the sugar the baby is used to is taken away and the baby’s blood sugar drops because there is no more insulin present.
While the risk of complications to both mother and baby increases with a newborn’s size, it doesn’t always mean a C-section delivery is necessary. The mother usually still has a choice if she wants to deliver vaginally. If she chooses a traditional delivery, she may receive an episiotomy (a surgical cut made at the opening of the vagina) or experience vaginal tears because special equipment like forceps may be used.
It is the most important to relax and not stress about baby’s size. However, Regular meetings and checkups with your birthing team are advised!