Marijuana Use Linked to Increased Risk for Preterm Birth

Emma Hitt, PhD

July 30, 2012

July 30, 2012 — Marijuana use and low body mass index are among many of the risk factors associated with increased risk for preterm birth, according to the findings of a large prospective study.

In particular, marijuana use was associated with a doubling of the risk for preterm birth.

"Regarding [tetrahydrocannabinol (THC), the active ingredient in marijuana], this study provides yet another warning about changing your lifestyle months and months before you try to conceive," principal investigator Gustaaf A. Dekker, MD, PhD, with the University of Adelaide, in South Australia, told Medscape Medical News.

According to Dr. Dekker, this is the first time THC has been linked to premature birth.

"Most additional concerns about THC come from the mental health literature, because of the now well-documented link between THC and psychosis — we do have concerns (by extrapolation of these mental health data) about THC and the fetal brain," he said.

The study is published in the July 2012 issue of PLoS One.

The current findings were derived from the Screening for Pregnancy Endpoints (SCOPE) prospective study of "healthy" nulliparous women, which was designed to develop screening tests for predicting preeclampsia, births of infants who are small for their gestational age, and spontaneous preterm births.

Follow-up was completed in 3184 participants, all of whom started the study at week 15 of gestation. Researchers collected information on all known clinical risk factors for preterm birth. Spontaneous preterm birth was defined as birth before 37 weeks' gestation and was classified as either with intact membranes or with rupture of the membranes.

Of the participants, 156 (4.9%) had a preterm birth, with about two thirds of those having intact membranes and one third having ruptured membranes.

Many risk factors for each type of preterm birth were noted. For preterm birth with membranes intact, these included a strong family history of low birth weight babies (~6-fold increased risk). In addition, a more than 2-fold increased risk was noted for each of the following risk factors: use of marijuana prior to pregnancy; mother with a history of preeclampsia; history of vaginal bleeds; and a mother with diabetes type 1 or 2.

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

  • Mild hypertension not requiring treatment (a 10-fold increased risk);

  • Family history of recurrent gestational diabetes (an 8-fold increased risk);

  • Receiving some forms of hormonal fertility treatment (a 4-fold increased risk);

  • Having a body mass index of less than 20 (more than a 2-fold increased risk).

According to the researchers, the dissimilarity of clinical risk factors for preterm births with and without intact membranes "indicates different pathophysiological pathways underlie these distinct sub-phenotypes of spontaneous preterm birth."

They add that although the analysis included over 3000 healthy women, identification of risk factors in the current study was based on only 156 women whose pregnancies were complicated by preterm birth.

"To identify risk factors for very-early preterm birth, much larger prospective cohorts will be required," they write.

The research was not commercially funded. The authors have disclosed no relevant financial relationships.

PLoS One. Published online July 16, 2012. Full article

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