“Optimal Time of Delivery”

This was an interesting abstract, which makes me want to read the full article. The objective was, “To estimate the gestational age ranges that result in optimal birth outcomes for each of four risk-defined groups.” What was most intriguing to me is that this is the first time I’ve seen an attempt made to look at “the best time for birth” for different risk groups, rather than putting everyone in the same category. The problem that occurs sometimes is that if there isn’t a proper delineation by risk factors, is that everyone gets “tarred by the same brush.” For instance, it’s known that smoking causes health problems for all people, including second-hand smoke in children, and maternal smoking in fetuses and neonates. I’ve previously talked about the risk of maternal smoking for babies — the infant mortality rate for the year 2000 was 10.7/1000 for smokers but 6.5/1000 for nonsmokers. If a study that looks at infant mortality rate doesn’t take into account maternal smoking, it may reach the wrong conclusion. Let’s say that a study looking at maternal hypertension and neonatal mortality finds that maternal hypertension increases the rate of neonatal mortality, but it didn’t look at only women who smoke or women who don’t smoke, or didn’t properly adjust the risk of neonatal mortality based on the known risk factor of smoking. The study may wrongly conclude that maternal hypertension alone may raise the risk of neonatal mortality X%, when the real cause of much of the increased risk is maternal smoking, and maternal smoking increases the risk of maternal hypertension and also neonatal death.

I’ve seen some people say that “the best time” for a baby to be born is 39 weeks, based on different factors (the people who have said that haven’t linked to studies, and I’m not sure I’ve read them, so I don’t know how they determine that — whether the “best” time is due to how many women have C-sections versus vaginal births, or perinatal deaths, or what), although I have recently read and blogged about a study that shows that elective C-sections at 37 and 38 weeks increase problems with neonatal morbidity compared to those done at 39 weeks. This study indicates that 39 weeks may not be the best for individual risk groups even if (and that’s a big “if”) it may be the case for the entire United States as a whole.

The restrospective study divided the women into four risk groups — the regular or low-risk group, maternal hypertension, advanced maternal age, and diabetic women — then looked at various outcomes (NICU admissions, Apgar scores, C-sections, etc.) to see which births on which gestational days had the best outcomes based on the day. The results were intriguing:

  • The low-risk group OTD (optimal time of delivery) was calculated to be 37 weeks 1 day to 41 weeks 0 day
  • the advanced maternal age group OTD was 38 weeks 5 days to 39 weeks 6 days
  • the hypertension group OTD was 39 weeks 2 days to 40 weeks 1 day
  • and the diabetes mellitus group OTD was 40 weeks 3 days to 41 weeks 1 day.

So it doesn’t appear that low-risk women should be offered an induction or C-section at 39 weeks, nor should the scare tactics start at going past 40 weeks 0 days, like it sometimes does. What is most interesting to me is that the DM group has better outcomes if the birth happens after the due date, but this seems to be the group that is typically induced or sectioned due to their risk status — typically “big baby” fears. But this seems to reject that notion. And the other two groups seem to do better closer to their due dates, but many women are induced (or offered an induction or C-section, or the doctors don’t turn down requests for inductions) at 37 or 38 weeks, because “well, you’re ‘term’ now so the baby can safely be born now, with no problems, and aren’t you tired of being pregnant?” In fact, it appears from these numbers that only babies born to low-risk moms do well if born in the first week and a half of term — that perhaps babies born to these higher-risk mothers benefit from more “womb time” than low-risk babies. Interesting.


5 Responses

  1. The study may wrongly conclude that maternal hypertension alone may raise the risk of neonatal mortality X%, when the real cause of much of the increased risk is maternal smoking, and maternal smoking increases the risk of maternal hypertension and also neonatal death.


    Are you aware that smoking appears to be slightly protective against the development of pre-eclampsia/hypertensive disorders of pregnancy? Not sufficiently protective to outweigh all the risks of smoking,but not a good example of what you are trying to explain.

    • Ergh. Now that you mention it, I faintly remember reading something about that. Do you have a study on-hand for that? I could try to find it, but if you’ve got it, it would save me a bit of time.

      It *should* be an accurate statement, dadgummit! 😉 After all, smoking raises blood pressure, so it ought to hold valid for pregnancy. Sigh…

      It makes me curious, though, as to why. I wonder if perhaps it has something to do with smoking causing bigger problems earlier in pregnancy (starting with reduced fertility, perhaps increasing the miscarriage/IUFD rate, preterm birth, etc.); and since preeclampsia typically strikes in later pregnancy, a reduced number/rate of smokers actually make it into p-e territory. IOW, smoking kills the weakest or otherwise prematurely brings pregnancy to an end, rather than letting them live until p-e strikes. Hmm… will need to investigate….

      • Actually, current thinking is that the roots of pre-eclampsia are already laid down in early pregnancy with placental implantation even if it only “strikes” in later pregnancy. Here’s one study


        But it is pretty much pre-eclampsia epidemiology 101. We just don’t trumpet it because we don’t want people to think smoking is fine in pregnancy (because it isn’t).

  2. Kathy, lovely post. I think I will check out that article. In my free time. You make some good points that everyone is not equal. Different folks will have different needs. I think that is very important and something that folks on the blogoshere really don’t point out clearly in their writing….So I am going to give you a 8 out of 10. but I won’t vote you off the island, you have immunity for this week….Cheers

    • Pinky,

      Thanks! I agree that “diff’rent strokes for diff’rent folks” is not always clearly delineated. It’s been a growing experience for me, being exposed to blogs like yours and N is for Nurse and other blogs that have to deal with the various risk groups, rather than being able to just have only low-risk women, with all other women “risked out” to OBs. For myself, I tend to get caught up in my own little world of low-risk women who would qualify for a home birth in just about anybody’s estimation, and tend to forget that many women do not qualify for that. So, I try to keep that sort of thing in mind. Doing a lot of research makes that easier — particularly the depressing studies and case studies on perinatal and infant mortality and such. I don’t like to do that sort of research, but it helps to keep me grounded.

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