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Male Marijuana Use Might Double the Risk of Partner’s Miscarriage

Most research on factors related to miscarriage has focused on women’s lifestyle or behavior, says study lead researcher. Photo by assalve/iStock

Male Marijuana Use Might Double the Risk of Partner’s Miscarriage

BU researcher finds that miscarriages are more likely when the father uses marijuana weekly

If a man habitually uses marijuana even as little as once a week, could that increase the risk of his partner experiencing a miscarriage in early pregnancy? A first-of-its-kind study suggests so.

By analyzing more than six years of lifestyle and behavioral data from 1,535 heterosexual couples actively trying to conceive, Boston University School of Public Health researcher Alyssa Harlow discovered that for men who use marijuana one or more times a week, their partner is twice as likely to miscarry than the partners of men who use marijuana less than once a week or not at all. The link persisted even after Harlow accounted for whether or not the men’s partners used marijuana themselves.

Most research on factors related to miscarriage has focused on women’s lifestyle or behavior, says Harlow, the study’s lead researcher. “But given that the human embryo is comprised 50 percent of the male’s genes, there’s been emerging interest in studying the role that men play,” she says.

Some studies have looked at caffeine and alcohol intake and found an association with increased rates of miscarriage, Harlow says. Until now, though, no one has looked at how male marijuana use affects miscarriage.

“There are [cannabinoid] receptors in human testicular tissue and sperm, and when a man uses marijuana, THC binds to these receptors,” Harlow says.

That knowledge, based on prior research examining the association between marijuana use and sperm quality, made Harlow and the other members of the research team curious about whether marijuana exposure could damage a man’s DNA or lower the quality of his sperm enough to result in a higher risk of his partner having a miscarriage.

“I’m really interested in the impact of substance use on pregnancy, and I’ve been watching the policy landscape change so rapidly around cannabis,” Harlow says. “I started reading more about marijuana and fertility, which helped us form the idea for this study.”

The analysis uses data from BU’s Pregnancy Study Online (PRESTO), a web-based study looking at lifestyle, dietary, and medical risk factors for pregnancy outcomes led by Lauren Wise, an SPH professor of epidemiology.

Harlow, who presented her findings this week at the annual meeting of the American Society for Reproductive Medicine, says that all forms of marijuana use—smoking, vaping, and ingesting—were part of the study, and that it’s not yet possible to parse those types of use apart to see if male use of one type has a higher miscarriage risk than the others.

For the women who miscarried, the median gestational time was six weeks of pregnancy. After eight weeks of pregnancy, the association between male marijuana use and miscarriage dropped off significantly. Harlow, an epidemiologist currently pursuing a PhD, says these findings support her hypothesis that male marijuana use compromises pregnancy at its early stages due to the changes it impacts on a man’s sperm. She says she’s looking forward to a peer review of the data and having the study’s results published in a scientific journal.

But she cautions that “one study does not a conclusion make. We need more studies before we can make any concrete recommendations. For couples trying to get pregnant, they should try to live as healthy a lifestyle as possible and talk to their doctor about marijuana use.”

Are you interested in being part of BU PRESTO? Visit the study website to learn how to enroll.

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Male Marijuana Use Might Double the Risk of Partner’s Miscarriage

Boston University epidemiological research finds that miscarriages are more likely when the father uses marijuana weekly.

So Does Using Marijuana In Pregnancy Hurt A Baby Or Not?

As more states legalize medical marijuana and recreational marijuana, questions about the drug’s effects on a fetus will become a more central public health concern. One significant flaw with most studies looking at marijuana use in pregnancy is that researchers do not take into account that a large proportion of marijuana users also smoke tobacco. Since negative effects from smoking during pregnancy are well-established, it could be that these outcomes are the ones being detected when researchers study marijuana use in pregnancy without adjusting for the effects of smoking.

The findings of a new study would seem at first to allay any concerns about that flaw: after adjusting for tobacco use, a combined analysis of more than two dozen studies found no increased risk of low birth weight, preterm birth or a handful of other poor outcomes among newborns whose mothers used marijuana during pregnancy.

But a closer look reveals the same problems that have plagued previous attempts to investigate all the research to date: there simply are not enough high-quality studies that provide enough data on enough pregnancies to separate out all the possible effects that could interfere with identifying effects from marijuana.

“When the authors go from the adjusted analyses to the further adjusted analyses, they have to dramatically reduce their sample size,” noted Aaron Caughey, MD, chair of the Department of Obstetrics and Gynecology at Oregon Health & Science University in Portland. “Thus, the negative findings of no increased risk for preterm birth or low birthweight could just be because of inadequate study power.”

It’s also important to note up front that this study, published in Obstetrics & Gynecology, focused only on a handful of possible risks at birth and only at birth. “We did not investigate long-term neurodevelopmental outcomes after exposure to marijuana in utero, and further study is warranted in this regard,” the authors wrote. In fact, few studies exist at all that look at long-term effects of marijuana use during pregnancy, and of the handful that do, which Emily Willingham and I analyzed for our book’s section on marijuana use, almost none take into account the use of tobacco, alcohol or other drugs, making it hard to know what effects from marijuana, if any, exist.

An activist smokes a marijuana joint prior to marching in the annual Hemp Parade (Hanfparade) on . [+] August 13, 2016 in Berlin, Germany. (Photo by Sean Gallup/Getty Images)

That lack of research is problematic given the drug’s prevalence. An estimated 2% to 27% of women use marijuana during pregnancy, but the number is hard to pin down because it’s almost certainly underreported due to stigma. Estimates also vary among different populations and according to how “use” is defined and how it’s detected.

Shana Conner, MD, of Washington University School of Medicine in St. Louis, and her colleagues combed six databases of medical research up through August 2015, eventually ending up with 31 studies ranging from 1982 through 2015 that met their criteria. They only included observational cohort and case-control studies in which they could separate the data on marijuana use from other substance use, including tobacco.

Among the 31 studies, 68% were conducted in the U.S. Together, the studies included 7,851 women who used marijuana during pregnancy and 124,867 who did not. Use of marijuana was based on either self-reporting from the mothers or from objective testing of the meconium, umbilical cord, urine, saliva or blood. The study did not distinguish between smoking marijuana and other forms of use, such as ingestion. (Almost no published studies examine ingested marijuana outcomes.)

The researchers primarily focused on outcomes of low birth weight (less than 5.5 lbs) and prematurity (born before 37 weeks of pregnancy), because these are the outcomes most often studied and because they are the most likely outcomes at birth based on what we know about the body. However, the authors also attempted to calculate the risks of stillbirth, miscarriage, being admitted to the neonatal intensive care unit (NICU) or a Level II nursery, low Apgar score, placental abruption, death during delivery and infants being underweight for their gestational week of birth.

Before making any adjustments for tobacco use or frequency of marijuana use, infants born to women who used marijuana were more likely to arrive early or have a low birth weight: 15% of marijuana-exposed newborns compared to 10% of newborns whose mothers didn’t use marijuana. But this increased risk dropped to statistical insignificance when the authors made either of two adjustments: distinguishing between women who used marijuana less than once a week versus those using it more often, or adjusting for tobacco use along with marijuana use. In both cases, using marijuana less than weekly or without tobacco did not lead to a greater risk of preterm birth or low birth weight. Using marijuana at least once a week doubled the risk of preterm birth or low birth weight.

When the authors analyzed all the numbers together from the seven studies that separately reported tobacco use and marijuana use, no increased risk of preterm birth or low birth weight showed up among those who used marijuana but didn’t smoke cigarettes. Similarly, after adjusting for tobacco use, the risk of placental abruption or an underweight newborn were no greater for newborns whose mothers used marijuana than for mothers who didn’t. Although the risk of a lower average birthweight, stillbirth or a low Apgar score was increased among infants exposed to marijuana, the researchers did not have enough data to calculate these risks after adjusting for tobacco smoking.

Again, that pesky problem of limited data means it’s hard to draw many strong conclusions from this study except that more higher-quality studies need to be done.

“I would remember that at baseline, all of the existing analyses have generally found increased risks of pregnancy complications,” said Caughey. “The current study finds that these risks are attenuated but cannot definitively state that there is no negative impact on the developing fetus.” Further, no current evidence suggests that there are beneficial effects from marijuana use during pregnancy, he said.

One requirement to determining whether exposure to a substance can cause a problem in the body is that a biological mechanism exists: there needs to be a clear path showing how the substance can have a direct, physical effect based on what we know about the body. In the case of marijuana, at least some possible biological mechanisms have already been identified. For example, the compound delta 9 tetrahydrocannabinol in marijuana easily crosses the placenta and remains in the adult body for up to 30 days, so its ability to reach the fetus and remain there means it could potentially affect fetal development. Past research has also found carbon monoxide levels in the blood after smoking marijuana were five times higher than levels after smoking tobacco. High levels of carbon monoxide in the blood could impede adequate oxygen levels in the blood, which could affect the fetus as well.

But data from large studies need to show possible effects, and the ones available aren’t adequate. For example, these authors found some evidence suggesting that more frequent use of marijuana did increase several risks at birth, but women who use more marijuana are also likely to smoke more and use other drugs, and the authors didn’t have enough information to separately analyze that.

So again, the biggest limitation to the whole analysis is that the studies included did not contain enough data for enough infants to reliably calculate risks for many of the outcomes the authors wanted to look at. That, combined with the lack of data (but theoretic risk) on neurodevelopmental outcomes or other long-term effects, means there is far too little evidence to say that marijuana in pregnancy has no negative effects.

“Alcohol and cigarettes were legal and used during pregnancy for many years and caused untold damage to developing neonates,” Caughey said, referring to fetal alcohol spectrum disorders and to effects from tobacco such as fetal growth restriction, stillbirth and preterm birth.

“Marijuana as a hallucinogenic drug that is inhaled has the potential to cause all of the problems seen in both of these legal drugs,” Caughey continued. “I would strongly recommend that all women using marijuana quit before attempting to get pregnant or when they learn they are pregnant.”

New findings suggest prenatal marijuana exposure doesn’t increase birth risks—but that’s not the whole story.