Pregnancy is full of anticipation, and it seems to start from the very beginning. Many patients are able to figure out their due dates immediately after their home pregnancy tests turn positive. We doctors and midwives count the days and weeks right along with you, so we can deliver the right care at the right time. As that due date approaches (often when the discomfort of the late third trimester sets in), patients begin to wonder “what happens if I go past my due date?”
A woman’s due date is set at the end of 40 completed weeks of pregnancy measured from the first day of her last menstrual period. About 65% of patients will deliver by then. We don’t know exactly what causes a normal pregnancy to extend past the due date, but there are some things that make it a little bit more likely. These include women who have never delivered before, male fetuses, mothers or fathers who themselves were born past their due dates and Caucasian race.
While most women who go past their due date will have a normal pregnancy, labor and delivery, there are some problems that can occur. Babies can be larger, and this can lead to more difficult vaginal deliveries that result in tears or excessive bleeding. Sometimes babies are too big to be born vaginally and a c-section is required. This is more likely the further a patient gets past her due date. The most concerning of these potential problems, however, is stillbirth. Thankfully, the rate of stillbirth in normal pregnancies is very low (about 1 per 1000). After a woman’s due date, this rate begins to increase slightly and continues to increase the further past she gets. It is important to remember that, despite this increase, the rate remains very low. However, a stillbirth is such a devastating event that we intervene to prevent it.
In the weeks after a woman’s due date, we look for signs the placenta is not working as well by monitoring the baby’s heart rate periodically or performing an ultrasound to look at the volume of amniotic fluid and certain baby movements that constitute a “biophysical profile.” If the testing is abnormal, an induction of labor may be recommended. With normal testing, we usually induce labor at 41-42 weeks gestation. This seems to be the optimal time to for reducing the risks of going too far past the due date while at the same time avoiding the risks associated with inducing too early.
As with most aspects of pregnancy, going past 40 weeks is an issue that that can trigger some anxiety for patients. Sometimes that big day feels like it will never come. As your due date approaches, it might help to talk with your doctor or midwife about it. They can help you understand that the slightly increased risks associated with post-date pregnancies are very manageable.
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