A new study has found that, among women with a high desire to avoid becoming pregnant, those who drank heavily had a 50% higher risk of becoming pregnant than those who drank moderately or not at all. In contrast, participants who used cannabis were no more likely to have an undesired pregnancy than participants who did not use cannabis.
From a larger sample of over 2,000 non-pregnant women aged 15-34, researchers identified a subgroup of 936 who didn't want to get pregnant. Within that subgroup, 429 reported heavy drinking (as measured using a standard alcohol screening questionnaire) and 362 reported using cannabis (including 157 who reported daily or almost daily use).
Those who drank heavily and those who used cannabis frequently had a higher overall desire to avoid pregnancy, compared with participants who drank moderately or not at all and participants who did not use cannabis.
Over the course of one year, 71 of the 936 women who most wanted to avoid pregnancy became pregnant. More than half of those undesired pregnancies (38) occurred among those who drank heavily, more than the combined number for those who drank moderately or not at all. In other words, heavy drinking was associated with a higher risk of undesired pregnancy compared with lower levels of drinking.
In contrast, less than half of the 71 undesired pregnancies (28) occurred among people who used cannabis, meaning that those who used cannabis did not show an elevated risk of undesired pregnancy compared with people who did not use cannabis.
Lead author Dr Sarah Raifman, of the University of California, San Francisco, School of Medicine, comments: "This study made two important findings. First, non-pregnant women who drink heavily appear, on average, to have a higher desire to avoid pregnancy than those who drink moderately or not at all. Second, drinking heavily as opposed to moderately or not at all appears to put those who most want to avoid pregnancy at higher risk of becoming pregnant within one year. Finding out why those pregnancies happen is the next step in our research."
"In the meantime, given the potentially life-altering effects of fetal alcohol spectrum disorders (which occur when a fetus is exposed to alcohol through the mother's drinking) and the fact that the risk of FASD increases with the amount and duration of the mother's drinking, it's important for doctors and clinicians to support women who drink heavily to stop drinking as soon as they suspect an unintentional pregnancy."
