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    Spontaneous preterm birth: preconceptional nutrition matters

     

    During a recent trip, I couldn't help observing the bulging waistlines of even the fairly well-to-do in Newport, Martha’s Vineyard, and Nantucket. It was a stark reminder that although the obesity epidemic in the United States has leveled off, nearly 36% of adults have a body mass index (BMI) ≥30 and thus are considered obese.1 Seeing several rather large pregnant women also reinforced the importance of a recent JAMA article that establishes a clear association between obesity and extremely early spontaneous preterm births.2

    Scope of the problem

    We are all very familiar with the general health risks attendant obesity, including an increased prevalence of cardiovascular diseases including hypertension, myocardial infarction, and stroke; as well as increased rates of diabetes, osteoarthritis, and certain cancers (eg, endometrial and breast). Indeed, analysis of the Framingham Heart Study suggests that nonsmoking women who are obese at age 40 have a 7-year reduction in life expectancy.3

    We are also increasingly aware of the reproductive sequelae of obesity. Obese women have significantly higher rates of preeclampsia, gestational hypertension, and gestational diabetes, which increase with increasing BMI.4 The fetuses of obese women are also at increased risk of congenital anomalies, death, and macrosomia, and, when there is maternal hypertension, intrauterine growth restriction.5,6

    A recently published study confirms increased rates of labor induction accruing obesity, from 25.3% in women with normal BMI to 42.9% in women with BMI ≥40.0, odds ratio (OR) 1.67 (95% CI, 1.43­­–1.93).7 Similarly, rates of primary cesarean delivery rise with increasing BMI and are highest among morbidly obese women (36.2% vs. 22.1% in women with normal BMI, OR 1.46 [95% CI, 1.23–1.73]).8

    Obesity and spontaneous preterm birth

    About the only major obstetrical outcome that seemed immune from the obesity epidemic was spontaneous preterm birth, although it has been appreciated for some time that obesity increases rates of indicated prematurity in women with hypertension and diabetes. Indeed, underweight women seemed at greater risk of spontaneous preterm birth. Well, this illusion also has recently been shattered.

    Exploiting the epidemiological power of the nationwide Swedish Medical Birth Registry, Cnattingius and associates analyzed the association between early pregnancy BMI and risk of preterm birth in 1.6 million women with live singleton births.2 Preterm births were stratified as extremely preterm (22–27 weeks), very preterm (28–31 weeks) and moderately preterm (32–36 weeks). Outcomes were further analyzed based on spontaneous and medically indicated preterm births. In the latter, obesity was associated with all 3 preterm birth categories but only in women with pre-existing hypertension or diabetes. In contrast, after adjusting for confounding, obesity was most closely linked to spontaneous extremely preterm births.

     

    Charles J. Lockwood, MD, MHCM
    Dr. Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South ...

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