You're pregnant, and so are some of your friends. Your obstetrician tells you no drinking ever while pregnant — not even one glass. Your friends' OBs tell them it's OK to have one glass occasionally. So who is right?

The truth is, we don't know.

A paper in the British Medical Journal Open reviewed previous studies on alcohol and pregnancy to see if it could determine what a "safe" level might be. In the United Kingdom, women are regularly told not to consume alcohol but also that they should limit it to one to two UK units once or twice a week or less than 32 grams of alcohol a week. That's confusing, right? Don't do it at all, or limit it?

The researchers looked at studies that tracked Mom's alcohol use and outcomes such as stillbirth, miscarriage, preterm births, hypertension, gestational diabetes, the kind of delivery, and, in the baby, size of head, Apgar score, cognitive development, behavioral problems, facial features and birth weight and size.

Here's what they found:

Very few studies looked at low levels of drinking and the outcome on pregnancy or the baby. Of the studies they found, there was nothing that showed a clear safe level of alcohol or at what point there was a clear detrimental effect. We just don't know at what point light drinking becomes harmful to the pregnancy or the baby.

The fear, of course, is miscarriage, stillbirth or premature birth, or fetal alcohol syndrome, which causes developmental delays, neurological problems, impulsiveness, hyperactivity, jitters and facial disfigurements.

"It's an irreversible injury," says Dr. John Thoppil of River Place Obstetrics and Gynecology. Fetal alcohol syndrome, he says, is now thought of as a spectrum disorder, but we don't know how little alcohol it takes for some of the effects to be seen in a baby.

The Centers for Disease Control and Prevention found in 2015 that 1 in 10 pregnant women reported they had at least one drink in the last 30 days, and 3.1 percent said they binge drank, consuming four or more drinks at one time.

"The best rule is no drinking," he says. "There's no amount of alcohol that is safe."

Yet Thoppil does couch his response with, "Is one drink going to cause an issue? Probably not, but one a week probably is too much."

Again, we don't know. What we do know is that alcohol goes freely through the placenta. "Would you allow your baby to have alcohol?" he asks.

What happens if you've been drinking regularly and then you find out you're pregnant? "Thankfully, early exposure is the least likely to be damaging," he says. Before eight weeks, it's about cellular growth, not as much rapid brain growth as it is after that part, he says.

Still, if you're planning on getting pregnant, he recommends avoiding alcohol.

At the University of Texas researchers at the Health Behavior & Research Training Institute at the Steve Hicks School of Social Work are part of the CDC's Collaborative for Alcohol-Free Pregnancy. Mary Velasquez, director of the institute, and Anita Prewett, project manager, have been working on substance abuse prevention during pregnancy for 20 years, working with places like treatment centers, jails and colleges — places where women who are at risk for alcohol use and are child-bearing age might be.

What they have seen in the last 20 years is that the rates of women drinking have increased and the amount they drink also has increased. Women are now just as likely as men to drink.

The rates also increase for women in their 30s and 40s, and drinking rates are higher in women with higher incomes and education levels, they say.

And in Austin, where there are places to drink even in the most unexpected places like the downtown public library, "It's part of the social fabric," Velasquez says.

They are trying to teach women to be aware of their drinking and to use contraception. "We don't want women to feel as though if you drink and get pregnant or if you drink and have sex you're a bad person," Velasquez says. "We want to raise awareness that she needs to be very, very thoughtful about her drinking, and if you're going to drink, be on contraception."

They are spreading the message that "there's no safe drinking level" in pregnancy.

Velasquez says much focus has been on pregnant women and illegal drugs or even prescription drugs. "In many cases, like cocaine, some of those outcomes can be reversed," she says, but the effects of alcohol on babies "can't be reversed."

The collaborative is also trying to work with doctors' associations such as the ones that represent obstetricians and family physicians to do alcohol-use screenings at regular doctor visits as well as ask about contraception. These screenings can be aimed at both men and women, whether they are child-bearing age, because we know that alcohol use has more dangers than just in pregnancy. Patients "like that attention in their doctor's office ... to have someone that cares," Prewett says.