Ask an OB: Does Mother Nature really know best?

"Ask an OB" is a weekly series with Dr. Maude "Molly" Guerin, MC, FACOG. If you have a question for her, please share it with us here. 

Why do doctors get nervous and want to induce women when they are overdue? Doesn’t Mother Nature know when the best time is? -- Skeptical Mom

Most of the time, she does. My three boys were 14, 12, and 10 days overdue – I had no non-stress tests, no ultrasounds, no discussion of induction, even though my blood pressure was high – and everyone lived!  My how times have changed in the last 30 years. The problem is that stillbirth does become more common as pregnancy advances, dramatically after 42 weeks – it’s 17 times higher after 42 weeks than it is at your due date. That being said, the chances are good that your baby will be fine even at 42 weeks – look at these numbers:

Completed Weeks	Stillbirth/10,000 births
37	2.4
38	3.6
39	4.0
40	2.6
41	9.4
>42	34.7

Obstetrics & Gynecology, VOL. 103, NO. 1, JANUARY 2004

So in today’s world, we like to get people delivered before 42 weeks. Usually once you pass your due date we are checking the amniotic fluid by doing a quick ultrasound once a week – this helps us know the placenta is still working well. Also doing a non-stress test by putting you on the monitor for 20 minutes twice a week helps us know the baby is doing well. These tests are not perfect, and our data on them is always being updated, but currently they are the standard of care and recommended by the American College of Obstetrics and Gynecology.

Here is a meta-analysis of studies on the management of post-dates pregnancy by the highly respected Cochrane Group:

Selection criteria

Randomised and quasi-randomised trials of interventions involving the intention to induce labour at a specified gestational age.

Main results

Twenty-six trials of variable quality were included. There were four trials of routine early pregnancy ultrasound, two of nipple stimulation, nineteen of routine versus selective induction of labour and one of antenatal fetal monitoring. Routine early pregnancy ultrasound reduced the incidence of post-term pregnancy (odds ratio 0.68, 95% confidence interval 0.57 to 0.82). Breast and nipple stimulation at term did not affect the incidence of post-term pregnancy (odds ratio 0.52, 95% confidence interval 0.28 to 0.96). Routine induction of labour reduced perinatal mortality (odds ratio 0.20, 95% confidence interval 0.06 to 0.70). This benefit is due to the effect of induction of labour after 41 weeks. Routine induction of labour had no effect on caesarean section.

In other words, induction of labor after 41 weeks reduced the chances of the baby dying by 80%. And since we never know if your baby is going to be one of the 9966 out of 10,000 who is fine, or be one of the 34 that is not – we want to get you delivered.

You can read more about Dr. Maude "Molly" Guerin, MD, FACOG, right here.