Last week at the Healthy Mothers, Healthy Babies Conference and meeting on Oct 7, 2014 in Macon, GA, Nicole Carlson presented information from her research on obesity in pregnancy. A few highlights to share from this conference, for those who were unable to attend:
Obesity in pregnancy is no longer a rare condition. Over a third of all childbearing women in the United States are currently obese, with up to 80% obesity among some racial and ethnic minority groups.2 Obesity has profound effects on both mother and baby during pregnancy. In the baby, maternal obesity increases the risk of congenital anomalies, macrosomia, and late third trimester fetal death.7, 10 Babies born to obese women have an increased risk of themselves developing diabetes, heart disease, and obesity later in life10. For the woman, obesity in pregnancy doubles her risk of having an unplanned cesarean, and obese women are more likely to have serious post-op difficulties when compared to normal-weight women.11
It is thought that obese women have more unplanned cesareans because they have very slow labors when compared to normal weight women.5 Hormones released by fat cells have been shown to diminish contractility at a cellular level in the uterus.8, 14 In addition, these same hormones are thought to slow down the ripening process for the cervix13 in obese women, resulting in longer gestations.1 The higher a woman’s BMI is during pregnancy, the more profound is the effect of these hormones on her labor.5
In the old days, when we were asked, “How long before labor is done and the baby arrives?”, healthcare providers would often use the standard of 1cm/hour in active labor to estimate cervical progress in labor. This standard speed of labor was based on the Friedman labor curve, first published in the 1950’s.3 It is now known that modern populations of women tend to progress through labor at a much slower rate than Friedman described over 60 years ago. More recent studies describing the labors of women all across the United States and in other countries have found that one-half of a centimeter per hour is probably a better estimate of labor progress for most women.9
Incredibly, labor progress in obese women is even slower than this estimate.5 It can take up to 6-9 hours (depending on her BMI) for an obese woman with a normal labor outcome to move from 4cm to 5cm! Labor becomes faster with higher cervical dilations in obese women, just as it does for normal-weight women. However, even at the fastest part of her labor, the obese woman still has slow labor progress compared to a normal weight woman (0.5 cm/hour in transition, between 7-8 cm). The good news is that obese women tend to have shorter lengths of the pushing stage of labor when compared to normal-weight women. However, many obese women never get the chance to push their babies out, because they receive a cesarean for abnormal progress in labor before they get to 10cm dilation. It is normal for an obese woman to move slowly through labor, and it is time for providers to stop comparing labor progress in the obese woman to that of a normal weight woman. Until we do, more unnecessary cesareans will result.
What is the busy midwife or doctor to do when faced with a slow labor in an obese woman? Unfortunately, obese women do not respond well to the most commonly used medication to correct slow labor progress: pitocin.12 They also tend to not respond well to cervical ripening medications.4 It appears that the best thing we as providers can do for our obese clients is to be patient. As long as her baby is happy and healthy, obese women should be supported through labor to have the best chances for a successful (and lower risk) vaginal delivery. Midwives have long based their care on the philosophy that women’s bodies are unique, and that the best care involves safely supporting normal physiologic processes. Although labor in the obese woman may be very different biologically from that of a normal-weight woman, the best birth outcome for most obese women will result from a renewed commitment by the healthcare team to allow women the time they need to do the work of labor.6
Bogaerts A, Witters I, Van den Bergh BRH, Jans G, Devlieger R. Obesity in pregnancy: Altered onset and progression of labour. Midwifery. 2013;29(12):1303-13.
Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999-2010. JAMA. 2012;307(5):491-7.
Friedman E. The graphic analysis of labor. Am J Obstet Gynecol. 1954;68(6):1568-75.
Gauthier T, Mazeau S, Dalmay F, et al. Obesity and cervical ripening failure risk. Journal of Maternal-Fetal and Neonatal Medicine. 2011:1-4.
Kominiarek MA, Zhang J, VanVeldhuisen P, et al. Contemporary labor patterns: the impact of maternal body mass index. American Journal of Obstetrics and Gynecology. 2011;205(3):244.e1-.e8.
Leeman L, Leeman R. A Native American Community with a 7% Cesarean Delivery Rate: Does Case Mix, Ethnicity, or Labor Management Explain the Low Rate? The Annals of Family Medicine. 2003;1(1):36 -43.
Mission JF, Marshall NE, Caughey AB. Obesity in pregnancy: a big problem and getting bigger. Obstet Gynecol Surv. 2013;68(5):389-99.
Moynihan AT, Hehir MP, Glavey SV, Smith TJ, Morrison JJ. Inhibitory effect of leptin on human uterine contractility in vitro. American journal of obstetrics and gynecology. 2006;195(2):504-9.
Neal JL, Lowe NK, Ahijevych KL, et al. “Active Labor” Duration and Dilation Rates Among Low‐Risk, Nulliparous Women With Spontaneous Labor Onset: A Systematic Review. Journal of Midwifery & Women’s Health. 2010;55(4):308-18.
O’Reilly JR, Reynolds RM. The risk of maternal obesity to the long-term health of the offspring. Clin Endocrinol (Oxf). 2013;78(1):9-16.
Poobalan AS, Aucott LS, Gurung T, Smith WCS, Bhattacharya S. Obesity as an independent risk factor for elective and emergency caesarean delivery in nulliparous women – systematic review and meta‐analysis of cohort studies. Obesity Reviews. 2009;10(1):28-35.
Walsh J, Foley M, O’Herlihy C. Dystocia correlates with body mass index in both spontaneous and induced nulliparous labors. Journal of Maternal-Fetal & Neonatal Medicine. 2011;24(6):817-21.
Wendremaire M, Goirand F, Barrichon M, et al. Leptin prevents MMP activation in an in vitro model of myometrial inflammation. Fundamental and Clinical Pharmacology. 2012;26:83.
Zhang J, Kendrick A, Quenby S, Wray S. Contractility and calcium signaling of human myometrium are profoundly affected by cholesterol manipulation: implications for labor? Reprod Sci. 2007;14(5):456-66.