Can drinking caffeine, getting too much exercise, or being in a bad mood really hurt your pregnancy? Two new studies reveal the truth about miscarriage risk.

By Lauren Gelman
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A positive pregnancy test sends a whoosh of excitement through your body. You start thinking, Will it be a boy or a girl? Which one of us will it look like? But then worry starts creeping in: What if something goes wrong and I have a miscarriage?

The chances of miscarrying aren't as high as you might think. For women younger than 35, it's 10 to 12 percent; for 35- to 39-year-olds, it's 18 percent. (It does rise to 34 percent for women 40 to 44 years old.) What's even more reassuring is that by the time you see a heartbeat on an ultrasound—usually by week six or seven—your chance of having a miscarriage drops to less than 5 percent, regardless of your age, says Michael Lu, M.D., associate professor of obstetrics and gynecology at the University of California, Los Angeles.

Here’s what you need to know about what does – and doesn’t – cause miscarriage.

The Causes of Miscarriage

Chromosomal Problems

Up to 70 percent of first trimester miscarriages and 20 percent of second trimester miscarriages occur because of a glitch in the fetus's genes, according to the March of Dimes. "When the chromosomes of the egg and those of the sperm fuse to form an embryo, they usually pair up correctly," says Henry Lerner, M.D., an Ob-Gyn at Newton-Wellesley Hospital in Newton, Mass. "But sometimes they get scrambled; if they're paired incorrectly, the embryo stops developing." It doesn't mean that anything's wrong with the mother or father. Plus, you're unlikely to repeat a chromosomal error the next time you conceive, so don't assume the past predicts your future.

Chronic Medical Conditions

Certain illnesses, especially those that restrict blood flow to the uterus, may increase a woman's chances of miscarrying (because the growing fetus can't get enough oxygen to survive). These include diabetes, thyroid disease, lupus, and heart disease, as well as others like uterine infections. Managing the condition before and during pregnancy can reduce miscarriage risk.

Hormonal Imbalances

Sometimes a woman's body doesn't produce enough of the hormone progesterone, which is necessary to help the uterine lining to support the fetus and help the placenta take hold. "Because this is not very common, we usually wouldn't test for it unless a woman's had multiple miscarriages," says Dr. Schaffir. Medication may improve the odds of a successful subsequent pregnancy.

Other Factors That Contribute to Miscarriage

Excess Caffeine Intake

Women who consumed 200 milligrams or more of caffeine each day (about two cups of regular coffee or five 12-ounce cans of caffeinated soda) had twice the miscarriage risk as those who didn't have any, according to a study by Kaiser Permanente in the American Journal of Obstetrics and Gynecology.

The cause isn't known for sure, but researchers suspect that the chemical crosses the placenta and can affect developing cells. While one cup of java or soda a day is probably fine, consider being extra-safe and switching to decaf entirely while you're actively trying to conceive and during pregnancy. "When so many other risk factors are out of your control, this is one of the few things you can do to improve your baby's health," says Tracy Flanagan, MD, director of Women's Health, Kaiser Permanente Northern California. "Why not err on the side of caution?" As always, if you have any concerns about what's safe for you, discuss them with your healthcare provider.

Excess Alcohol, Cigarette, and Drug Use

Had a glass of wine or two before you knew you were expecting? Don't worry – that's not the level of use we're talking about here. "It's exposing a fetus to large amounts of these chemicals on a regular basis that can cause miscarriage, because they have a poisonous effect on all those developing cells," says Jonathan Schaffir, MD, an assistant professor of obstetrics and gynecology at Ohio State University College of Medicine. But as soon as you suspect you're expecting or a test confirms it, cut out the cocktails, cigarettes, and such for good.

What Doesn't Cause Miscarriage

Despite how common miscarriages are, many women are surprisingly in the dark about what actually triggers them, according to research from Ohio State University College of Medicine.

"Much misinformation is shared among women or passed down from older generations," says Dr. Schaffir, who authored the study. "It's important for women to understand that these are just old wives' tales – and not only are they not true, but in some cases, believing them can affect your health and wellbeing." We asked him to debunk the major misconceptions from the Ohio State University study here.

Miscarriage Myth: Too Much Exercise

Fact: Exercising picking up a (reasonably) heavy object—a grocery bag, a toddler, or the like—are extremely unlikely to cause a miscarriage. In fact, most experts agree that exercise during pregnancy – with your doctor's okay – can lower miscarriage risk and make mom and baby healthier (by reducing stress, aches and pains, gestational diabetes risk, and even building up stamina for labor).

Miscarriage Myth: Your Mood Plays a Part

Fact: With all those hormones surging, moodiness is a given during pregnancy – and no studies have ever linked excessive bad moods to miscarriage, says Dr. Schaffir. But if you find yourself in a funk you can't shake, let your doctor know. As many as 10 or 20 percent of women experience depression during pregnancy – which may not trigger miscarriage or harm the pregnancy, but should be treated by your doctor.

Miscarriage Myth: Too Much Stress

Fact: While some studies on stress and miscarriage are conflicting, Dr. Schaffir says that everyday tension or anxiety – tight deadlines at work or worrying about what labor will be like – has not been linked to pregnancy loss. "We're talking big things, like the death of a spouse or parent," he explains, and even then, the link is not well established. Plus, women under extreme stress are also more likely to smoke, drink, or do drugs, which can affect miscarriage.

Miscarriage Myth: Could It Be Mom's Fault?

Fact: The vast majority of miscarriages occur because of chance chromosomal or genetic abnormalities in the unborn baby or, less commonly, hormonal imbalances or problems with the uterus or placenta, says Dr. Schaffir – nothing that a mom-to-be has control over. “It's natural for a woman experiencing loss to try to explain it in some way, even if that means blaming herself," he says. "But all women need to know that most of the time, a miscarriage is completely random, and odds are you will get pregnant after trying again."

When to Try Again After Miscarriage

After an early pregnancy loss, it's safe to try again as soon you get your next period – a sign that your uterus is functioning normally again, says Dr. Schaffir. But as always, get the green light from your doctor first and alert him or her right away when you suspect you're pregnant.

And know this: Since most miscarriages are completely random, having one usually does not increase your odds for another pregnancy loss.  In fact, for the majority of women who have a miscarriage, the chances of a successful next pregnancy are 80 percent. "After two miscarriages in a row, your risk does go up slightly, but most doctors won't start testing for genetic, uterine, or hormonal problems until you've had three," says Schaffir.



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