Pregnant women know drinking alcohol and smoking cigarettes is never good for an unborn baby's health. However, when it comes to marijuana, some expectant moms will admit it helps alleviate their morning sickness.

Now, researchers at Lawson Health Research Institute, Western University and Brescia University College in Canada have found smoking weed while pregnant can almost triple the odds of having an infant with low birth weight. The team found maternal amphetamine use, chronic hypertension, and maternal marijuana use were the top risk factors linked with low birth weight.

The researchers included live births between February 2009 and February 2014 in their analysis; those with a birthweight of less than 5.5 pounds were classified as low birth weight; while preterm birth was defined as a live birth before 37 weeks of gestation. A total of 15.6 percent of women reported smoking during pregnancy. Prenatal smoking was responsible for 6.4 percent of low birth weight and and 9.7 premature birth. The rates are comparable to those reported by the Canadian Institute for Health Information in 2010-11, which found 6.6 percent of infants in Canada had low birth weight, and 8.1 percent were preterm births.

“Low birth weight and preterm birth are serious public health problems. Both are associated with a higher risk of infant mortality,” said Dr. Jamie Seabrook, principal investigator, a Lawson associate scientist and professor at Brescia University College, in a statement.

Read More: Smoking Weed While Pregnant Linked To Low Birth Weight, Stays In Intensive Care

Currently, the World Health Organization estimates more than 1 in 10 babies are born preterm (before 37 weeks of gestation). Common causes of preterm birth include genetics, age, nutrition, prenatal care, and smoking. However, the new study, published in the Journal of Biosocial Science, has found marijuana use has a stronger effect than other factors, like socioeconomic status, on the adverse birth outcomes.

Seabrook and his colleagues' main objective sought to determine whether socioeconomic status had an influence on birth outcomes. Previous research has confirmed infant mortality rates are highest among mothers from disadvantaged backgrounds. For example, a 2010 study found infants born in low socioeconomic areas had the worst infant mortality rates and the highest racial disparity, specifically in the city of Milwaukee among African American infants. These infants were at three times greater the risk than white infants for adverse birth outcomes.

The researchers believe the link between socioeconomic status and low birth weight was not seen because of universal healthcare in Canada compared to the lack thereof in the U.S.

"It's possible that Canada's universal health care system provides a larger safety net for these mothers and their children,” said Seabrook.

Read More: Women Who Use Cannabis Through Week 20 Of Gestation At Higher Risk Of Preterm Birth

Contrastingly, a study on pregnant mothers in Jamaica before and after pregnancy, found those who used marijuana to remedy their morning sickness did not have infants with low birth weight or compromised neurological development. In fact, these babies showed better social skills than the babies who were born to mothers that didn’t use marijuana.

However, improvements are not linked to marijuana itself. Rather, the researchers conclude it's due to how the babies were raised. The researchers believe a mother’s lifestyle influenced the health of her baby. For example, mothers who used marijuana were also vendors of ganja, meaning they were home most of the time after birth, allowing them to be more attentive to their child’s needs.

There have been many studies that analyze the effects of marijuana on a developing fetus, but there’s still more research to be done. Studies tend to rely on the mother’s self-report on marijuana use, which can lead to under-reporting usage for personal reasons. Researchers need to devise better methods to measure maternal use of weed during pregnancy.

We do know smoking weed is a modifiable risk factor.

Women who are pregnant or trying to get pregnant should understand the possible effects it can have on an unborn baby to reduce the risk of adverse birth outcomes, like low birth weight or premature birth.

Source: Campbell EE, Gilliland J, Dworatzek PDN et al. Socioeconomic status and adverse birth outcomes: A population-based Canadian sample.” Journal of Biosocial Science. 2017.

See More:

Marijuana Use Before Pregnancy More Than Doubles the Risk of Premature Birth

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