Despite risks to fetuses and infants, increasing numbers of women appear to be using marijuana in the year before they become pregnant as well as early in their pregnancy, according to a Kaiser-Permanente study published last week.

The study reported on the results of early pregnancy surveys taken about eight weeks into the pregnancies of nearly 277,000 Northern California women from 2009 through 2017.

The research was reported last week in the online journal, JAMA Open Network. (JAMA stands for Journal of the American Medical Association.)

Some of the women were pregnant more than once during the period of the study, so survey responses covered 367,403 actual pregnancies.

Marijuana use during pregnancy has been found to increase the risk of impaired neurodevelopment and babies with low birth weight, according to medical authorities.

The American College of Obstetricians and Gynecologists, for example, recommends that women who are pregnant or contemplating pregnancy stop using cannabis, the psychoactive drug in marijuana.

The Kaiser study found that that self-reported cannabis use nearly doubled during the period of study.

From 2009 through 2017, the proportion of surveyed women who said they used cannabis in the year prior to pregnancy rose from 6.8 percent to 12.5 percent, the report said.

During the same nine years, the proportion of women who used cannabis even after they were pregnant rose from 1.9 percent to 3.4 percent.

In a Kaiser staff publication, Kelly Young-Wolff, a research scientist in Kaiser’s division of research, estimated that “the actual numbers are likely higher, as women may be unwilling to disclose their substance use to a medical professional.”

She also speculated that marijuana use may have risen further after the study ended because recreational use of cannabis was legalized in California in 2018.

The risks to the newborn are real, however. “These (published) findings should alert women’s health clinicians to be aware of potential increases in daily and weekly cannabis use among their patients,” she said.

The percentage of women who self-reported using cannabis varied by daily, weekly and monthly use. All increased, but “daily use increased most rapidly,” according to the research findings.

Findings with regard to Northern California Kaiser patients paralleled national statistics, which also indicate rising cannabis use among U.S. adults. Urine toxicology studies at Kaiser also tend to support the survey findings, according to an internal Kaiser article.

The study was also supported by a grant from the National Institutes of Health abuse. It called for further research to learn more about the use of cannabis later in pregnancy as well as trends that might have developed since California legalized recreational cannabis use in 2018.

The Kaiser article noted that “some women may use cannabis during pregnancy to manage morning sickness.”

It also supposed that some women may get the impression from cannabis product marketing and online media that cannabis use is safe during pregnancy.

However, it continued, “There is substantial evidence that exposure to cannabis in pregnancy is associated with having a low birthweight baby, and the American College of Obstetricians and Gynecologists recommends that women who are pregnant or contemplating pregnancy discontinue cannabis use because of concerns about impaired neurodevelopment and exposure to the adverse effects of smoking.”