In the past week, I have heard two rather disturbing stories from my Prenatal Yoga Center students. One told me the unlikely unfolding of her birth story: she hit her due date, and the doctor predicted she was going to have a baby weighing nearly 10 pounds. Because of this “guestimation” of the baby’s size, her doctor strongly urged her to have a Cesarean section due to concerns about shoulder dystocia (a rare pregnancy complication which I go into further detail about below). The mother reluctantly agreed to have the surgery and gave birth to a beautiful baby girl weighing in at 8 pounds, two ounces.
The second story involves a second-time mother approaching her due date. She had a very quick delivery with her first child, giving birth to a 7 pound baby two weeks early. Her doctor, like the one in the first story, is concerned that this full-term baby will be too big for the mother to birth given that her first baby was already seven pounds at 38 weeks. So the doctor wants to induce on her due date.
What’s so alarming about these stories? That there can be a significant margin of error in estimating fetal birth weight and that these doctors may be practicing out of fear, or what I call “defensive medicine.” In other words, they are assuming there is a problem before a problem presents itself.
I do have empathy for the position doctors are in, since obstetrics can be a tricky field and the care provider is responsible for the well-being of the mother and the child. But there needs to be some trust in the fact that the human race would not have survived if our bodies were inherently broken.
Back to the topic at hand: estimation of fetal weight. The average margin of error in birth weight predicted by sonogram is estimated to be between 6 and 15 percent. Also, sonograms obtained before 37 weeks result in fewer errors in predicting true birth weight than sonograms obtained after 37 weeks. If a pregnant mother is continuing to have sonograms to estimate fetal weight up to the end of her pregnancy, there is going to be an even higher chance of miscalculation.
So if your care provider is telling you at 41 weeks that your baby is estimated to be over 9 pounds, you may want to take into consideration the higher chance of inaccuracy that occurs this late in the pregnancy when deciding what to do.
This brings us to the next important question: what are the risks of delivering a “big baby?” I personally have seen perfectly healthy large babies–over 9 pounds–born vaginally. My own doctor agrees that most of the time big babies can be born vaginally if the baby is in a good fetal position.
The main risks are: undetected gestational diabetes (which means the baby could be at risk of having a low blood glucose level), third- or fourth-degree vaginal lacerations, and an increased risk of Cesarean section. The most disconcerting risk, which is very rare, is shoulder dystocia. Shoulder dystocia occurs when the baby’s head is delivered but the anterior shoulder is caught on the mother’s pubic bone or, even more rarely, when the posterior shoulder is caught on the mother’s sacrum.
Although rare (occurring in 0.6-1.4 percent of all infants between a birth weight of 5 lb 8 oz to 8 lb 13 oz and increasing to a rate of 5 to 9 percent among infants weighing between 8 lb 13 oz and 9 lb 14 oz) shoulder dystocia presents risks to both the baby and mother. The Royal College of Obstetricians and Gynecologists states that 10 percent of babies with shoulder dystocia may experience brachial plexus injury (temporary nerve damage of the baby’s neck), with only 1 percent suffering permanent nerve damage. The baby may also experience a fracture of the clavicle (collar bone) or humerus (arm bone). In the vast majority of cases, these injuries heal without a problem. In extremely rare and severe cases, hypoxic brain injury or death may occur. The mother may also suffer injury from third-degree vaginal tears, postpartum hemorrhaging and the emotional impact of a traumatic experience.
It may seem overwhelming and even scary to read about possible negative outcomes from shoulder dystocia, however it is important to see the numbers in context. The chance of occurrence is very low and the chance of permanent damage extremely low. Also, there are several safe maneuvers a care provider can use to help dislodge the baby should it get stuck. For example, the Gaskin Maneuver, named after midwife Ina May Gaskin, has undergone numerous studies with very positive outcomes.
It is upsetting how many times expectant mothers tell me their doctor wants to induce them for suspected big babies. Some of these mothers are even encouraged to be induced before their due dates. The birth of your child is something that you will carry with you for the rest of your life. It is your baby’s first introduction into the world and the first of many experiences you will share together. If it is not a medical necessity to be induced, allow yourself and your baby the opportunity to see how your story together starts on its own.
