A night out at the bar might increase your risk of an unwanted pregnancy, a study suggests. 

Researchers in California surveyed 2,200 young women, approximately 40 percent of whom explicitly said they did not want to get pregnant. 

Of the women who said they did not want to become pregnant, about half were heavy drinkers, meaning they had at least four drinks during a night out. 

The researchers found heavy drinkers were about 30 percent more likely to accidentally become pregnant compared to women who regularly used cannabis instead of drinking.

They were also more likely to get pregnant than their peers who consumed alcohol more sparingly or steered clear of it entirely. 

The findings come as younger generations increasingly shun alcohol. However, binge drinking has increased specifically in Gen Z women in recent years.

Women are also having fewer children than ever before, citing high costs and a greater focus on building a career. 

It’s unclear exactly why drinkers are more likely to get pregnant accidentally, but researchers suggest it could be because drinking is more socially acceptable than using cannabis. 

Alcohol is also thought to lower inhibitions more and lead to riskier behavior like unprotected sex than using cannabis.

Women who drink heavily may be more likely to accidentally get pregnant (stock image)

The study, published last month in the journal Addiction, looked at 2,270 women enrolled at primary and reproductive health clinics in Arizona, California, New Mexico, Texas and Nevada. 

Participants were between ages 15 and 34 and none of them were pregnant. All of them had had sex within the past three months. 

Women completed quarterly surveys over one year about their demographics, substance use, pregnancy preference and pregnancy history. 

Of the 2,270 participants, 936 said they did not want to get pregnant. Among them, 429 reported heavy alcohol use – four or more drinks in one occasion – and 362 said they regularly used cannabis. 

Among cannabis users, 157 said they used it daily or almost daily.

Both heavy drinks and frequent cannabis users were more likely to report not wanting to get pregnant compared to those who drank lightly or not at all and those who didn’t use cannabis. 

Over the course of a year, 71 of the 936 women – seven percent – who didn’t want to become pregnant ended up getting pregnant. And 38 of those pregnancies occurred in women who drank heavily.

This was more than the combined total pregnancies in women who drank moderately or didn’t drink at all. 

Meanwhile, 28 unintended pregnancies occurred in the cannabis group, showing a 30 percent increased risk in women who drank heavily compared to those who used cannabis. 

The new study comes as more women are putting off having children (stock image)

Dr Sarah Raifman, lead study author and researcher at the University of California – San Francisco, said: ‘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.’

It’s unclear exactly what caused this increased risk, though the researchers speculated alcohol may be more likely to cause risky behaviors and forgetfulness, such as remembering to take birth control. 

Alcohol is also more widely accepted and practiced than using marijuana and has more consistently been shown to lower inhibitions. 

There were several limitations to the new study. Researchers wrote they were unable to precisely measure substance use over time, and it’s possible participants underreported their usage. 

Dr Raifman said: ‘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.’