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Are you at risk for a preterm birth?

Robin Wulffson MD's picture
preterm birth, marijuana, smoking, gestational diabetes, hypertension

A preterm infant is one born at less than 37 weeks of gestation. These children may suffer life-long disabilities as a result of coming into the world too early. Australian researchers conducted a large study to identify risk factors for preterm birth. They published their findings in the July issue of the journal PLoS ONE. Among the many factors increasing the risk were marijuana use and being too thin (low body mass).

For example, marijuana use doubled the risk of preterm birth.

The goal of the study was to identify risk factors for spontaneous preterm birth with intact membranes (SPTB-IM) and SPTB after rupture of the membranes before the onset of labor (SPTB-PPROM) for nulliparous (no previous deliveries) pregnant women. The study group was comprised of 3,184 women; 156 (4.9%) had their pregnancy complicated by SPTB and 60 (1.9%) experienced either SPTB-IM or SPTB-PPROM. The researchers identified the following independent risk factors for SPTB-IM: shorter cervical length, abnormal uterine Doppler flow, use of marijuana pre-pregnancy, lack of overall feeling of well-being, being of Caucasian ethnicity, having a mother with diabetes and/or a history of preeclampsia (toxemia), and a family history of low birth weight infants. Independent risk factors for SPTB-PPROM were: shorter cervical length, short stature, participant’s not being the first born in the family, longer time to conceive, not waking up at night, hormonal fertility treatment (excluding clomiphene (Clomid)), mild hypertension, family history of recurrent gestational diabetes, and maternal family history of any miscarriage (risk reduction). Low body mass index (BMI (less than 20) nearly doubled the risk for SPTB-PPROM (odds ratio 2.64; 95% CI 1.07–6.51).

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The researchers found that the following factors to carry the greatest risk for preterm rupture of membranes leading to birth included the following:

  • Mild hypertension not requiring treatment (10-fold increased risk);
  • Family history of recurrent gestational diabetes (8-fold increased risk);
  • Receiving some forms of hormonal fertility treatment (4-fold increased risk);
  • Having a BMI of less than 20 (more than a 2-fold increased risk).

The researchers concluded that the ability to predict PTB in healthy nulliparous women using clinical characteristics is modest. They noted that the dissimilarity of risk factors for SPTB-IM compared with SPTB-PPROM indicates different pathophysiological pathways (causes) underlie the distinct and disparate risk factors.

Take home message:
This study pointed out a number of different risk factors for preterm birth. The risk factors fall into two categories: those that a woman has some control over and those that she does not. Those that she has control over primarily included lifestyle choices. Smoking tobacco or alcohol increases the risk as does alcohol or drug abuse. A low body mass index also is a correctible factor. Those that one does not have control over include one’s genetics and family history. If a woman possesses some of these factors (i.e., mild hypertension or family history of gestational diabetes), she should discuss them with her obstetrician. Fetal surveillance (i.e., non-stress testing and other monitoring methods) can reduce the risk of preterm labor.

Reference: PLoS ONE

See Also:
US preterm birth rate worst among developed nations
Infertility treatment linked to birth defects
Preterm birth reported to increase risk of psychiatric disorders
Prolonged standing at work may harm fetal development