Marijuana Use Before Pregnancy Doubles Risk of Premature Birth

by Brian M. Williams

MarijuanaLighting up? If you're planning a pregnancy in the future, you might want to rethink recreational drugs.

Using marijuana before pregnancy more than doubles a woman's risk of giving birth to a baby prematurely, according to a new study published in journal, "PLoS ONE."

Lead author Professor Gus Dekker, clinical director of the Women’s and Children’s Division at the Lyell McEwin Hospital in Adelaide, said smoking marijuana raised the risk of preterm birth from the average of 7 or 8 percent, to between 15 and 20 percent.

About the Study

The latest study of more than 3,000 pregnant women in Australia and New Zealand has revealed some of the most common risk factors for having a premature baby.

First time moms carrying a single baby were recruited for the study. They were less than 15 weeks pregnant and had no underlying medical conditions that might modify pregnancy outcome.

The participants were examined and interviewed by a midwife. Questions included those about diet, vitamins, drug usage and lifestyle before pregnancy, during the first trimester and at 15 weeks. A psychological scale measure perceived stress, depression and anxiety. The information was entered into a central database.

The women were followed, with pregnancy outcome data and baby measurement collected by research midwives.

Risk Factors for Preterm Birth

The research team found that the greatest risks for spontaneous preterm birth included:

  • Strong family history of low birth weight babies (almost six times the risk)
  • Marijuana use prior to pregnancy (more than double the risk)
  • Having a mother with a history of preeclampsia (more than double the risk)
  • Having a history of vaginal bleeds (more than double the risk)
  • Having a mother with diabetes type 1 or 2 (more than double the risk)

Risk factors for preterm rupture of membranes leading to birth included:

  • Mild hypertension not requiring treatment (almost 10 times the risk)
  • Family history of recurrent gestational diabetes (eight times the risk)
  • Receiving hormonal fertility treatment (almost four times the risk)
  • Underweight with a body mass index of less than 20 (more than double the risk)

Decker said it was possible that some of the women continued to smoke marijuana during their pregnancy.

"Women are much more open to acknowledge on their booking visit that they were regular users and during their pregnancy they often deny it, although we know that they often still do it,'' he said.

"We are unable to determine whether this association is due to a toxic effect of marijuana or is a marker of a suite of lifestyle factors that contribute to the risk,'' the authors wrote.

"Better understanding the risk factors involved in preterm birth moves us another step forward in potentially developing a test -- genetic or otherwise -- that will help us to predict with greater accuracy the risk of preterm birth. Our ultimate aim is to safeguard the lives of babies and their health in the longer term," Decker concluded.


Medical references:
- Dekker, G, et al. (2012) "Risk Factors in an International Prospective Cohort of Nulliparous Women" PLoS ONE 7(7): e39154.