The Mysteries of Miscarriage

Each year, 4 million parents welcome new babies. More than 1 million others lose theirs before they're born. Why? It's the question of the month, after a headline-grabbing study said women who reported consuming more than 200 milligrams of caffeine a day doubled their risk of miscarriage--from the 12 percent among non-using participants to 25 percent. (A 12-ounce "tall" Starbucks coffee contains 260mg.) Latte lovers flooded doctors' offices with anguished queries. The hysteria is "like an epidemic," says Yale University Ob-Gyn Mary Jane Minkin, author of "The Yale Guide to Women's Reproductive Health."

Caffeine, of course, isn't the only culprit. The list of factors that plays a role in miscarriage is long, and not all of them can be controlled. Or understood. More than half of all miscarriages are caused by chromosomal abnormalities. "It's nature's way of saying, 'this isn't working, so we're going to let it go'," says Duke University Ob-Gyn Susann Clifford. Random chromosomal error causes 70 percent of pregnancies that end before six weeks of gestation, 50 percent of pregnancies that stop between six and 10 weeks and only 5 percent of pregnancies that end after 10 weeks.

Women cannot do much about some risk factors, such as previous miscarriages and advanced maternal age. "You can't change your age, and you can't change your history. It's a frustrating business," says Mount Sinai School of Medicine epidemiologist David Savitz. Older women are simply more likely to conceive embryos with chromosomal abnormalities, such as Down syndrome. In the general population, the risk of miscarriage after six weeks gestation is 15 percent. At age 35 it's 25 percent and at age 40 it's 42 percent.

There are steps that women of all ages can take to lessen other potential risks--even before they conceive. "Good preconception care is probably your best bet," says Dr. Uma Reddy, a medical officer for the National Institute of Child Health and Development. "By the time you come and see your Ob at 11 weeks, it's already too late." Before and after conception, take prenatal vitamins (which include folic acid), don't smoke, avoid second-hand smoke and toxic chemicals, and maintain an ideal body weight. Obesity increases the risk of miscarriage (and birth defects) and is emerging as a significant risk factor for stillbirth, says Reddy. Eating undercooked meat can increase exposure to the bacteria listeria, to E. coli and to the toxoplasma parasite. Cleaning the litter box of an outdoor cat, who may eat an infected bird or rodent, also increases the risk of toxoplasmosis.

Staying calm is important, as well: a British study last year added to the mounting evidence that stress may increase miscarriage risk. (This is the kind of advice that drives already-anxious women crazy, unfortunately.) Avoid alcohol and illicit drugs, such as marijuana, cocaine and heroin. And use acetaminophen (Tylenol) instead of ibuprofen (Advil), which can decrease the amount of amniotic fluid around the baby, says the NICHD's Reddy. To be safe, avoid sushi and limit consumption of fish high in mercury levels, such as canned tuna, says Dr. Diane Ashton, deputy medical director of the March of Dimes. And avoid soft cheeses like brie and gorgonzola, which may contain the bacteria listeria. Limit exposure to chemicals such as home pesticides, mercury and gasoline--but be realistic. "We're not going to recommend that pregnant women never fill their car," says Ashton. Make sure you're vaccinated against chicken pox and rubella (before trying to conceive) since anything that can cause birth defects may also cause miscarriage. And, to repeat the latest news, don't overdo caffeine, which crosses the placental barrier and increases blood pressure and heart rate.

Other potential risk factors require further study. Hot tubs and microwaves ovens, for example, have not received much research attention. Dr. De-Kun Li, the lead author on the caffeine study, has examined them, however, and he tells women to stand at least five feet from a microwave oven, and to stay out of hot tubs since they may raise core body temperature. (In a hot tub, a woman can't sweat to cool off.)