Marijuana Use By Pregnant Women Increasing In California, Study Finds

Ahead of California starting the sale of marijuana for recreational use, come Jan. 1, a study published Tuesday found that in the years between 2009 and 2016, the number of pregnant women in the state who used marijuana after conceiving rose from 4.2 percent to 7.1 percent. The study was based on both self-reported data and toxicology reports of almost 280,000 women who were part of the Kaiser Permanente Northern California healthcare system.

The rise in cannabis consumption by pregnant women corresponds to about 7.5 percent growth every year, but there is a marked disparity when that number is broken down by age groups. In 2009, one in eight pregnant women under the age of 17 used marijuana, but that number grew to over one in five by 2016. During that period, the figures for pregnant women aged 18-24 jumped from under one in 10 to almost one in five. In comparison, just over one in 20 women between the ages of 25 and 34, and fewer than one in 30 women older than 34, were using marijuana while pregnant in 2016.

This age-based difference in weed consumption seems to have been around for longer. Based on self-reported data alone for past-month use, an older study from January 2017 found the number of adult pregnant women using pot grew from 2.4 percent to 3.9 percent between 2002 and 2014, while the aggregated percentage of adolescents who were pregnant and using pot during the same period stood at 14.6 percent.

The self-reported data, however, was not entirely trustworthy, which is to say, use of marijuana during pregnancy was often underreported on voluntary reports. The cannabis toxicology (which, along with the self-reported use questionnaire, was part of the standard prenatal care) consistently showed higher use than reported by the women themselves. More than half the women with a positive result on prenatal marijuana use showed up positive on toxicology only.

Survey that rely on self-reporting use of marijuana during pregnancy “likely underestimate use due to social desirability bias and underreporting, leaving the scope of the problem unclear,” the study’s authors wrote, qualifying their decision to include urine toxicology data for their own research

According to the Centers for Disease Control and Prevention, “mothers may put their babies at risk of health problems when they expose them to marijuana during pregnancy” because the chemicals in marijuana can be transferred from a pregnant woman to her child. These health problems could be even worse if the marijuana was consumed by smoking it, but it may be bad for the child in any form, the CDC says on its website.

An advisory for healthcare providers by the American College of Obstetricians and Gynecologists also says the use of marijuana by women who are pregnant, planning to be pregnant or are breastfeeding should be discouraged.

The study, titled “Trends in Self-reported and Biochemically Tested Marijuana Use Among Pregnant Females in California From 2009-2016,” appeared in the Journal of the American Medical Association.