The average pregnancy lasts 40 weeks, but only around 5% of all babies are born on the exact due date assigned by a healthcare provider. It’s important to remember that due dates are estimates, most often calculated as 40 weeks from the first day of your last menstrual period. Many assumptions are made with this calculation – that you ovulated on exactly Day 14 of your last menstrual cycle, that your cycles are 28 days long – so it’s unsurprising that this one-size-fits-all model simply can’t be accurately applied to all expecting mothers. Many babies will arrive early, while many others will be born after their due date.
The negative health consequences for babies born prematurely (i.e. before week 37) are very well studied, but more recent research has also focused on the potential negative effects of babies born too late. Post-term pregnancies, defined as pregnancies lasting into the 42nd week, are associated with higher rates of perinatal mortality. This is likely because as the placenta ages, it becomes less efficient at delivering oxygen and nutrients to the baby. In 2011, the country of Denmark adopted a policy to induce labor during the 41st week of pregnancy (or in the 40th week for mothers over 40 years old) instead of waiting until the 42nd week, which resulted in a decline in the national rates of stillbirths and perinatal deaths. Babies born post-term are also more likely to have macrosomia (birth weight greater than 8lbs., 13oz), which increases the rates of birth trauma and cesarean section. Babies born post-term also have higher rates of meconium aspiration syndrome, when a baby has a bowel movement in the amniotic fluid and breathes in the fluid after birth, which is usually not fatal but can lead to infections and long-term breathing problems.
Because of these complications, many OB/GYNs choose to schedule an induction after prolonged gestation. The American College of Obstetrics and Gynecology supports the consideration of induction at 41 weeks of pregnancy and recommends induction during week 42. Individual healthcare provider preferences vary, but your doctor will likely bring up the topic if your estimated due date is rapidly approaching without any signs of action.
If you remain pregnant at 40 weeks, your provider will probably order an additional ultrasound to ensure that there is still enough fluid in your amniotic sac and the umbilical artery is still effectively delivering blood to the baby. Other tests your doctor might order include a nonstress test, which monitors the normal variances in the baby’s heartbeat, and a contraction stress test, which monitors the variations in the baby’s heartbeat in response to a contraction.
If your due date has come and gone but if your fetal monitoring test results look good, then the best thing you can do is relax until you and your doctor decide that it’s time to be induced. Try to get some rest and enjoy the calm before the (wonderful) storm surrounding the arrival of your little one!
Hussain AA, Yakoob MY, Imdad A, Bhutta ZA. Elective induction for pregnancies at or beyond 41 weeks of gestation and its impact on stillbirths: a systematic review with meta-analysis. BMC Public Health, 11(Suppl 3): S5, 2011.
Lockwood D. ACOG Practice Bulletin Number 146: Management of Late-Term and Postterm Pregnancies, August 2014. Obstet Gynecol, 124:390-396, 2014.
Zizzo AR, Kirkegaard I, Pinborg A, Ulbjerg N. Decline in stillbirths and perinatal mortaility after implementation of a more aggressive induction polidy in post-date pregnancies: a nationwide register study. Acta Obstst Gynecol Scand, 96(7):862-7, 2017.