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Say it together now: Women know their bodies. Women can video of sex position the jackhammerbe trusted with their bodies.

It's not every day that a reputable study comes along to support these obvious truths, given that women, of course, still routinely hear patronizing messages -- including from the medical community -- about things like menstruation, birth control, abortion and childbirth.

Now a new study provides strong evidence that medical guidelines issued last year about pregnancy and alcohol use underestimated women.

The research, published Thursday in Obstetrics and Gynecology,essentially finds that women actually know how to make decisions about their bodies. The study was spurred by controversial recommendations issued last year by the Centers for Disease Control and Prevention, which advised women planning to get pregnant and sexually active women who don't use effective contraception not to drink alcohol because of the chance of a fetus developing fetal alcohol spectrum disorders (FASDs).

The blowback was mighty, with critics arguing the recommendations could basically apply to all women capable of conceiving. The logic of the guidance also implied that women might not change their alcohol use once learning they were expecting, so they shouldn't drink at all.

Though there are debates about the effects of moderate versus heavy drinking during pregnancy, the CDC states that there is no safe time to drink during pregnancy, nor a safe amount.

The controversy caught the attention of Katherine Hartmann, deputy director of the Institute for Medicine and Public Health at Vanderbilt University. An obstetrician and researcher, she'd already been conducting a study on early pregnancy that happened to include information on alcohol use. So she took a second look at her data to see if women continued to use alcohol during pregnancy.

Lo and behold, she found the opposite. More than half of all women reported that they drank in their first trimester, but ninety percent of them stopped once realizing they were pregnant. Even most who kept indulging quickly reduced their intake from two drinks a week to less than one.

Overall, women who planned their pregnancies had 31 percent lower odds of drinking around the time of conception and during early pregnancy compared to women who'd become unexpectedly pregnant.

"I take heart that this data tells me women are aware of their bodies," Hartmann said. "They are making good decisions ... We just found it so heartening that behavior immediately changed."

When Hartmann took a closer look at those who continued to drink, she made a surprising discovery. Women who were older, white, college-educated, made more money and were pregnant with their first child, were the most likely to throw one back.

That's important because the CDC's recommendations hinted that some women weren't being careful enough, and in the history of moralizing about motherhood, it's often low-income, women of color who are the targets for such blame.

While Hartmann's study isn't nationally representative -- she used a demographically diverse sample of 5,036 women from eight communities in three states -- her findings provide the basis for some real talk about who may be at most risk.

Women younger than 21 also used alcohol while pregnant, and though rare in the sample, episodes of binge drinking were associated with being younger, unmarried, a past or current smoker and using illicit drugs.

The solution to the larger problem of preventing FASDs, says Hartmann, isn't to unrealistically expect tens of millions of women of reproductive age to stop drinking because they might get pregnant. A more strategic approach to reduce drinking and the risk of FASDs would be to target the six million women who are planning pregnancies or having sex without contraception with more practical interventions.

Since women appear to stop or reduce alcohol consumption once they see a positive pregnancy test, Hartmann says it would be wise to emphasize testing as early as possible.

So if you're hoping to get pregnant but still nursing that glass of pinot at the end of the day, don't put off peeing on a stick if your period doesn't arrive on time. The same approach goes for women who aren't planning a pregnancy but have sex without reliable contraception and miss a period.

An obvious policy solution, says Hartmann, is ensuring that every woman has access to affordable birth control. She also urges physicians to ditch their preconceived notions about who might be more likely to drink during pregnancy and instead screen all of their patients.

The CDC, which reviewed Hartmann's study Thursday, said in a statement that the agency "encourages women to talk to their healthcare provider about their plans for pregnancy, their alcohol use, and ways to prevent pregnancy if they are not planning to get pregnant."

Wendy Kline, the who researches the history of medicine at Purdue University, criticized the CDC's guidelines last year but welcomed the conclusions made by Hartmann and her co-authors.

"In general, I think this is a more intelligent response," says Kline, who was not involved in the new study.

As for why some white, educated, middle-class women may not strictly follow the guidelines after learning of their pregnancy, Kline speculates that could be a "political act" rooted in their belief of reproductive choice. In other words, they may see it as preserving their individual autonomy versus being reduced to an incubator.

For those women, exercising their personal rights could include having a glass of wine at the end of a stressful day without being made to feel guilty. They may also see high-profile debates over the science of drinking during pregnancy, or look at European women who drink moderately without fear of FASDs, and feel like the risk is overstated.

Regardless of their rationale, Hartmann's study is an important reminder that women can act quickly and decisively when it comes to drinking during pregnancy, and public health officials might consider coming up with messages that show more trust in their ability to do just that.