Effects of Marijuana Use During Pregnancy Remain Illusive

Apr 01, 2017

Dual users of weed and tobacco face pronounced risks

According to a recent Gallup poll, one in eight Americans smoke marijuana. As for the nation’s middle and high school students, most have started using the drug between the 8th and 10th grades. The U.S. Department of Health and Human Services National Institutes of Health (NIH) reports that teens’ perceptions of the risks of marijuana have steadily declined over the past decade – possibly related to increasing public debate about legalizing or loosening restrictions on the drug for recreational and medicinal uses.

But the number of youngsters smoking marijuana, or “weed,” is telling. In 2015, NIH studies revealed that 11.8 percent of 8th graders reported marijuana use in the past year and 6.5 percent were current users. Among high school sophomores, 25.4 percent had used marijuana in the last year and 14.8  percent were current users. Rates of use among high school seniors were higher – 34.9 percent had used marijuana the year prior and 21.3 percent were current users. Some (six percent) reported using marijuana daily or near-daily. These students will ultimately become adults. And some, who are female, will bear children. So the question begs: What is marijuana’s effect on the fetus? The short answer is, the jury is still out.

Negative effects are plausible

According to NIH’s National Institute on Drug Use, animal research suggests that the body’s neural system receptors play a role in controlling the brain’s maturation, particular in the development of emotional responses. Thus, THC (tetrahdrocannabinol – the main mind-altering ingredient found in marijuana) exposure very early in life may negatively affect brain development.

Research in rats, the NIH reports, suggests that exposure to even low concentrations of THC late in pregnancy could have profound and long-lasting consequences for both brain and behavior in offspring. Human studies have shown that some babies born to women who used marijuana during their pregnancies respond differently to visual stimuli, tremble more, and have a high-pitched cry – which would indicate problems with neurological development.

NIH contends that school children prenatally exposed to marijuana are more likely to show gaps in problem-solving skills, memory and the ability to remain attentive. Medical researchers agree that more research is needed to segment marijuana’s specific effects from environmental factors and use of other substances by mothers.

Because roughly half of U.S. pregnancies are unplanned – with the rate considerably higher for teens and young adults – many women use marijuana without knowing they are pregnant.

A different school of thought

The American College of Obstetrics and Gynecology reports that somewhere between two percent and five percent of  women say they used marijuana while pregnant. And since the drug crosses the placenta, harm to the fetus is plausible although the evidence is still unreliable. A review and analysis of 31 previously published studies have found no independent connection between marijuana use and adverse births.

However, there are “confounding” factors for low birth weight and preterm delivery with tobacco use which is a common combination. Shayna Conner, an assistant professor in the division of maternal fetal medicine and ultrasound at Washington University in St. Louis School of Medicine concludes that from available evidence the risk surrounding low birth weight and preterm delivery is from tobacco use and other factors – not from marijuana.

However, Conner is not advocating that expecting mom’s use this info as the green light to roll a joint and get high. “Any foreign substance that doesn’t directly benefit maternal or fetal health should be avoided,” she says. There are several reasons not to smoke marijuana. For starters, the body of evidence on whether or not marijuana is harmful to the fetus is inconsistent. Second, little has been done to research long-term risks of neurodevelopment problems – cognitive difficulties or ADHD – in babies exposed to marijuana in the womb.

“Any time there is a substance that we’re not sure of the effects on the fetus or the mother during pregnancy, unless we know of a strong benefit to using the substance, we’d advise not to use it, says Torri Metz, an assistant professor of maternal-fetal medicine at the University of Colorado Denver.

The smoking gun

Reuters Health reported on a U.S. study which concluded that women who used both marijuana and cigarettes while pregnant delivered smaller babies, delivered earlier, experienced asthma as well as pregnancy-related hypertension (high blood pressure).

The study was conducted to see what effects marijuana alone or in combination with cigarettes might have on both mother and baby. The study team analyzed 12,069 women who gave birth between January 2011 and June 2015 at hospitals associated with Baylor College of Medicine.

Of the entire group, just less than one percent (or 106 women) reported marijuana use while pregnant. Half of this number, 48, said they also smoked cigarettes while pregnant. Researchers found that women who smoked both marijuana and cigarettes were more than twice as likely as women who used neither substance to experience asthma; two and a half more times as likely to deliver prematurely; two and a half more times to have pregnancy-related high blood pressure; and nearly three times as likely to have babies with small heads or low birth weight.

Additionally, the study, reported on in Reuters Health, concluded women who used both substances were more likely than the others to have diabetes and high blood pressure before pregnancy. One other study conclusion is that women who used only tobacco during pregnancy or only marijuana – and those  who used both – were also four to seven times more likely than women who used neither to have depression or anxiety.

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Tonia Wright

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