Labor Length in "Obese" Women: Dig Deeper

Here's the abstract of an interesting study suggesting that the first stage of labor (dilation) is longer in "obese" women and that this ought to be taken into account when diagnosing labor arrest needing a cesarean in this group.

This is not the first study to find a longer length of labor in higher-BMI women. As a result of these differences, one study concluded:

It is critical to consider differences in labor progression by maternal prepregnancy BMI before additional interventions are performed.

I agree that a possible longer labor length ought to be taken into account before resorting to a cesarean. As we've discussed before, many cesareans are done for "Failure to Wait" rather than for a true emergency, and many cesareans in women of all sizes could probably be avoided if care providers were a little more patient during labor.

In fact, a recent joint statement from the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine suggested that women be allowed a longer time in early ("latent") labor, that women not be considered to be in "active labor" until 6 cm (instead of 4 cm), and that they be given more time both in active labor and in the pushing stage before the doctor starts thinking cesarean.

This may be especially meaningful for high BMI women, as there tends to be a lower surgical threshold for women of size. In one study, labor in obese women was terminated by cesarean an hour earlier on average than in other women. This shows that some doctors are nervous in the labors of obese women and jump to a surgical solution far too quickly.

On the one hand, it is understandable that doctors are nervous about doing a truly emergent cesarean in obese women, since accessing the baby takes longer and the surgery is more difficult. On the other hand, if doctors jump to cesareans too quickly, many obese women who might have given birth vaginally are exposed to the substantial risks of surgery. And since many women of size these days are strongly discouraged from VBAC, this often means further cesareans, which is even more risky.

It's important to acknowledge that it can be difficult for providers to judge whether or not labor should continue in obese women with slow labors. However, provided the fetus is doing well, this study suggests that care providers should be more patient in the labors of women of size. 

Yes! That's something I've been saying for a while now.

Digging Deeper

However, I'd also like researchers to dig even further into why our labors may be longer.

There is some research to suggest that women of size have higher rates of posterior (OP) babies, and OP babies often have prolonged labors. I wish this study's database had fetal position recorded so they could have checked out this possibility.

Do obese women really have more posterior babies? Is that why they tend to have longer labors and more cesareans for dystocia? Or is it a relative lack of responsiveness to oxytocin, as some authors have suggested?

A number of older studies on obesity and pregnancy noted higher rates of fetal malpositions, particularly OP. Most newer studies have not looked for a connection, although the study linked above does note higher OP rates in obese women. Anecdotally, my own birth stories and the birth stories of many fat women I've received over the years for my website seems to support the idea of a higher rate of malpositions as well. All this suggests a connection, but of course we need data to back that up.

I would love to see someone, somewhere research the fascinating question of whether women of size have more malpositioned babies and whether this is one factor behind slower labor rates in this group. I'm sure it's not the only factor, but I would guess that it is a significantly underestimated factor.

If you are a woman of size reading this post, don't panic and think you're doomed to have a really long labor just because you are heavier. On average, our labors tend to be longer, but there's no way to predict labor length for any one person.

SO MUCH of labor length has to do with the position of the baby, whether or not labor is induced, how ripe the woman's cervix is, whether the woman can be mobile in labor, and many other factors. I've known fat women who have had 2 hour labors, and I've known fat women who have had very long labors. My own four labors varied from 8 hours to nearly 20 hours ─ same-sized woman every time but the difference was well-positioned babies vs. OP babies. So labor length really can be highly variable, even within the same person's experiences.

Summary

A combination of a tendency towards longer labor and a lower surgical threshold for cesarean, along with more inductions, is probably why the cesarean rate in high BMI women has risen so high. Because obese women have more complications with cesareans, it is important to discover how to lower this rate.

The take-away message from this study is that, on average, the labors in high BMI women were longer, and their care providers probably should take that into account and wait a little longer before diagnosing a labor arrest disorder and doing a cesarean.

If you are a woman of size, find a care provider who truly believes that you can have a vaginal birth and who is willing to be more patient in labor before resorting to a cesarean. (Generally speaking, midwives tend to be more willing to wait, although some OBs are great about this too. Don't depend on a title but ask careful questions to better understand a provider's practice style.)

If you are a researcher, dig a little deeper and explore why women of size have longer labors, including whether or not there is a higher rate of fetal malpositions. I suspect there is but I'd love to see recent data to confirm this.

If there are more OP babies in heavier women, then there are things that women of size can do that might help lower their chances of a malpositioned baby before labor (chiropractic care is what helped me). Additionally, there are things a care provider can do during labor to help turn a malpositioned baby if needed (research on manual rotation is very promising). And of course, sometimes all that's needed for an OP baby is to have a little more patience in labor.

Whether it's being more patient in labor, doing fewer inductions, or being more proactive about fetal position in women of size, there are things we can do to lower the cesarean rate in this group. It's about time we start doing them. 


Reference

Eur J Obstet Gynecol Reprod Biol. 2013 Nov;171(1):49-53. doi: 10.1016/j.ejogrb.2013.08.021. Epub 2013 Aug 29. Maternal body mass index and duration of labor. Carlhäll S1, Källén K, Blomberg M. PMID: 24041847

OBJECTIVE: To evaluate whether the duration of the active phase of labor is associated with maternal body mass index (BMI), in nulliparous women with spontaneous onset of labor. STUDY DESIGN: Historical prospective cohort study including 63,829 nulliparous women with a singleton pregnancy and a spontaneous onset of labor, who delivered between January 1, 1995 and December 31, 2009. Data were collected from the Perinatal Revision South registry, a regional perinatal database in Southern Sweden. Women were categorized into six classes of BMI. Overweight and obese women were compared to normal weight women regarding duration of active labor. Adjustments were made for year of delivery, maternal age and infant birth weight. RESULTS: The median duration of labor was significantly longer in obese women (class I obesity (BMI 30-34.9) = 9.1h, class II obesity (BMI 35-39.9) = 9.2h and class III obesity (BMI > 40) = 9.8h) compared to normal-weight women (BMI 18.5-24.9) = 8.8h (p < 0.001). The risk of labor lasting more than 12h increased with increasing maternal BMI: OR 1.04 (1.01-1.06) (OR per 5-units BMI-increase).The risk of labor lasting more than 12h or emergency cesarean section within 12h, compared to vaginal deliveries within 12h, increased with increasing maternal BMI. Duration of the second stage of labor was significantly shorter in obese women: in class III obesity the median value was 0.45 h compared to normal weight women, 0.55 h (p < 0.001). CONCLUSION: In nulliparous women with a spontaneous onset of labor, duration of the active phase of labor increased significantly with increasing maternal BMI. Once obese women reach the second stage they deliver more quickly than normal weight women, which implies that the risk of prolonged labor is restricted to the first stage of labor. It is clinically important to consider the prolonged first stage of labor in obese women, for example when diagnosing first stage labor arrest, in order to optimize management of this rapidly growing at-risk group of women. Thus, it might be reasonable to adapt the considered upper limit for duration of labor, according to maternal BMI.