Gestational diabetes and the best time to give birth

There’s a fair bit of controversy about whether, how, and when to test for diabetes in pregnancy. This post focusses on one decision women with a diagnosis of diabetes are often asked to make – when to give birth. (If you are after information about other aspects of diabetes in pregnancy, Rachel Reed and Sara Wickham both have great blogs about this, and both have books on induction of labour.)

Why shorten pregnancy duration for women with diabetes?

It’s believed that certain outcomes become increasingly more common as a woman’s blood glucose levels rise – particularly pre-eclampsia, having a big baby, stillbirth, and giving birth by caesarean section. It isn’t always entirely clear whether some of these outcomes relate to the underlying changes in physiology or to the current ways women with a diagnosis of diabetes are cared for. In an attempt to reduce the chance of these outcomes, women with a diagnosis of diabetes are often recommended to give birth around about a particular number of weeks of pregnancy.

The number of weeks that is recommended as the “do not go past this date” point has little evidence behind it. In other words, it was chosen because it seemed like a good idea. There is starting to be some research to help identify the best timing, and today’s post explores a recently published paper exploring the question of when is the best time for women with diabetes to give birth (Nashif, et al., 2023).

How was the research done?

The research team took data from eleven hospitals in Minnesota USA, that had already been collected as part of routine maternity care. The data started with 64,441 women who gave birth between January 2011 and May 2021. Women with one baby who had either Type I or II diabetes before pregnancy, or with gestational diabetes, who gave birth between 36 and 41 weeks and 6 days, to a baby with no chromosomal abnormality or major birth defect, were included in the study. They then divided this group up according to whether they had a “diabetes-indicated birth” in any given week from 36 to 41, or were still pregnant at that time, regardless of the way they gave birth. Women whose labour started on its own, or who were induced or gave birth by caesarean section for a reason other than diabetes (e.g., they were induced for prelabour membrane rupture), were removed from the data set.

They ended up with 1,449 women with a planned birth between 36 and 40 weeks for a diabetes related reason. The outcomes for women and babies were then noted, according to the week of birth.

What did they find?

Babies born at 36 and 37 weeks were more likely to be admitted to the nursery, and to remain admitted for longer, than those born to women who were still pregnant during these weeks (and therefore gave birth later). At 38, 39, and 40 weeks there was no longer a significant difference in admission rates to the nursery compared with ongoing pregnancy. The length of any admission was also no different between birth in the 38th or 39th week compared to ongoing pregnancy, but was shorter for birth in the 40th week rather than ongoing pregnancy at that point.

Rates of shoulder dystocia were higher at 36 weeks compared to ongoing pregnancy. Respiratory distress was higher at 36 – 38 weeks, and low blood glucose levels for the baby were more common at 36 to 39 weeks compared with ongoing pregnancy. There were no differences in stillbirth or neonatal death rates. Death was uncommon, with five stillbirths and six neonatal deaths. The stillbirths were mostly unrelated to diabetes, and included a true cord knot, trisomy 21, and abruption.

Tucked away in Table 1 are the mode of birth findings. While they provide a breakdown of vaginal, caesarean, and assisted births, there is no additional information to tell us whether the caesarean births were prior to induction of labour or after it. Vaginal birth rates were higher in ongoing pregnancies at 36 and 37 weeks, and not different between planned birth at 38 to 40 weeks compared with ongoing pregnancy at those gestations. Caesarean section rates among those who gave birth in a given week were lowest at 40 weeks compared with earlier gestations.

Also in Table 1 are birth weight data. There were no significant differences in birth weights at any gestation between women who gave birth that week, and those who remained pregnant. In other words, waiting an extra week or two didn’t result in the baby being suddenly much bigger, which is reassuring.

What does this mean for women with diabetes?

Paying attention to the fine print of this study is quite important. In research-land we use the term generalisability. The word captures the idea that what we learn from any one piece of research may or may not be relevant to everyone, but it is reasonable to expect women in a similar situation will have similar outcomes to those in the research.

This is NOT a trial that tells us anything about whether women are better served by waiting for labour to start on its own. The findings do support the author’s conclusion that there is little to support recommending birth before 39 weeks for women with diabetes. In practice, obstetricians will argue that poor outcomes occur more often for women with diabetes that began before pregnancy than for gestational diabetes, and for women who have used medications to control their gestational diabetes than those who controlled their sugars without this, and therefore recommend birth at different times for women with different types of diabetes. This trial doesn’t give us any information about whether this is justified or not.

Is induction a forbidden word?

As I read this paper, one thing stood out to me about the word choices the authors used. Nowhere in the paper was the word “induction” ever used. There was simply no way to tell how many women had labour induced and how many gave birth by caesarean section before or rather than after, an attempt at induction. This would be useful information. Exposure to labour does make a difference to perinatal outcomes, so being able to measure this is important.

This avoidance of the word “induction” is something I have noticed increasingly over the past five years or so. There seems to have been a shift in obstetric language to use “timing of birth”or “planned birth”. It does provide a shorter option than saying “births after induction of labour or prelabour caesarean section”, so I can understand why it might be used.

But this choice worries me. It seems to imply it doesn’t matter how labour starts, as long as it happens at a particular number of weeks. Have we lost sight of the well established benefits seen in research with spontaneous labour onset? The extremely complex physiology responsible for spontaneous labour onset is mostly trigger by the fetus, signalling it is now optimally prepared for life outside the uterus. These physiological changes also prepare the woman’s body for the upcoming labour and for lactation.

While there are occasional exceptions, spontaneous labour onset reduces the chance of complications for woman and baby. I think we risk losing sight of this by using terms like “timing of birth” rather than induction of labour. The concept of induction as an intervention seems to disappear from view. It is replaced by a suggestion that all babies can be ordered to arrive on schedule where the only decision is when.

References

Nashif, S. K., Mahr, R. M., Tessier, K. M., Hoover, E. A., Ajagbe-Akingbola, O., Chiu, E., Andrews, J. I., Sabol, B. A., Rogers, W. K., & Wernimont, S. A. (2023, Aug 9). Neonatal outcomes and rationale for timing of birth in perinatal diabetes: a retrospective cohort study. American Journal of Obstetrics & Gynecology MFM, 5(10), 101129. https://doi.org/10.1016/j.ajogmf.2023.101129

Sign Up for the BirthSmallTalk Newsletter and Stay Informed!

Want to stay up-to-date with the latest research and course offers? Our monthly newsletter is here to keep you in the loop.

By subscribing to the newsletter, you’ll gain exclusive access to:

Exciting Announcements: Be the first to know about upcoming courses. Stay ahead of the curve and grab your spot before anyone else!
Exclusive Offers and Discounts: As a valued subscriber, you’ll receive special discounts and offers on courses. Don’t miss the chance to save money while investing in your professional growth.

Join the growing community of birth folks by signing up for the newsletter today!

Subscribe to the newsletter