Ah…the due date. The question everyone always asks. The day that is circled, highlighted and starred on your calendar.
It is so easy for the awaiting mother (not to mention her family) to get very attached to this date. However, according to the American College of Obstetricians and Gynecologists (ACOG), only 5 percent of babies arrive on their exact due date.
Full-term gestation is seen as anywhere from 37 to 42 weeks–so it’s more like a due month than a due date. There are a few different ways to determine a due date. One way is by ultrasound, another is by measuring the uterus, and the most common is Naegele’s rule, in which the due date is calculated by taking the first day of your last period, counting back three months, and then adding seven days. However, this calculation assumes that every woman has a regular 28-day cycle and ovulates on day 14. If the pregnant mom has a longer cycle, therefore ovulating later, she will likely have a longer gestation period and her given due date may be off.
To make things more complicated, a study done through the Harvard School of Public Health found that uncomplicated, spontaneous-labor pregnancy is longer than Naegele’s rule predicts. To determine the due date, the authors recommend counting back three months from the first day of the last menses, then adding 15 days for primiparas (a first-time mother) or 10 days for multiparas (a mother that has already given birth).
Given the wide range of interpretation and accuracy involved in determining due dates, it is important for pregnant women to discuss with their health practitioners what their protocol is for passing one’s due date–since, according to the data above, the date isn’t necessarily accurate to begin with.
Throughout my years working with pregnant women, I have encountered some care providers that allow mothers to reach the full gestation period of 42 weeks before induction, while other care providers induce 10 days, one week or even one day after the due date. If the care provider is open to the mother’s need for more time, the expectant mother will likely go through a battery of tests to assure the continued health of both herself and her child. Those tests are:
Kick counts. This is a completely noninvasive test that can be done at home, and can be a reliable way to keep track of baby’s well-being. The mother counts the baby’s kicks felt over a specific amount of time and keeps track of the pattern. (The ACOG recommends writing down how long it takes the baby to make 10 movements.)
Nonstress test. This test measures the baby’s heart rate at rest and during an active period. It is done with an external fetal monitor and an external monitor measuring uterine contractions.
Biophysical profile. This test combines the results of the nonstress test and an ultrasound to measure the volume of amniotic fluid and check the baby’s breathing, movement, heart rate and muscle tone.
Contraction stress test. This test measures the baby’s heart rate during a contraction to assess how the baby is handling the reduction of oxygen during the contraction.
Mother’s blood pressure and protein in urine. The care provider will monitor the mother’s blood pressure and check for protein in the urine to assure the mother is not developing preeclampsia.
If a mother passes her due date of 40 weeks and would like more time before considering an induction, she can ask to try some natural alternatives to induce labor, which I’ve written about extensively here.
It is rather uncommon to actually pass 42 weeks of gestation. In fact, only about 7 percent of babies are not delivered by this point. Pregnancies passing the 42-week mark are referred to as “post-term pregnancies” and usually involve the care provider inducing labor to avoid serious complications.
