Factors you can control
Many women fear that exercising, falling, lifting heavy objects or the like can trigger a miscarriage, but the chances of that happening are slim. "Unless you are a smoker, illicit-drug user or heavy drinker, there's very little you can do to cause a miscarriage," notes Lerner, the author of Miscarriage: Why It Happens and How Best to Reduce Your Risks (Perseus). "Even a typical car accident or fall won't cause one." However, a recent Swedish study found that pregnant women who were exposed to secondhand smoke were 67 percent more likely to miscarry than those who weren't.
Certain health conditions also predispose some women to miscarriages. Thyroid problems, diabetes, genital-tract infections, obesity--all can put a pregnancy at risk. That's why it's important to try to get such conditions under control before you conceive.
Being underweight is somewhat of a risk factor too. Women who are underweight prior to pregnancy (with a body mass index, or BMI, under 18.5) are 72 percent more likely to miscarry in the first trimester, according to a new British study of more than 600 women. However, underweight women reduced their miscarriage risk by half if they ate plenty of fruits and vegetables and took nutritional supplements during early pregnancy. Those taking folic acid, iron or multivitamin supplements fared best.
What's age got to do with it?
While scientific advances and lifestyle changes can address many of the causes of miscarriage, there's one they can't fix. "The incidence of miscarriage increases exponentially with a woman's age," says Lesley Regan, M.D., the director of the Recurrent Miscarriage Service at St. Mary's Hospital in London and a clinical professor in the Division of Surgery, Oncology, Reproductive Biology and Anesthetics at Imperial College of London.
According to Hummel, a woman age 35 or younger has a 15 percent chance of miscarriage; as she nears 39, her chances are 20 percent; her chances are 30 percent at age 40; and her risk nears 40 percent if she is 42 or older. "At birth, a woman has all the eggs she'll ever have," explains Lerner. "The older she gets, the more time she has for her eggs to be damaged by such environmental insults as noxious chemicals, gases and heavy metals. There's an inevitable amount of degeneration over time."
According to research published in the Journal of Andrology, scientists now suspect that the father's age--particularly if he is over 40--may also be a factor in miscarriage, although a much smaller one than the mother's age.
When to get help
While most experts agree that a single miscarriage doesn't warrant investigation, they differ on what constitutes recurrent miscarriage--and therefore when you should seek help. "The general rule of thumb is that a woman should see a doctor after three sequential miscarriages, but I think that's too liberal," Hummel says. "I believe that any woman under 35 who has had two miscarriages in a row should seek treatment; if a woman is older than 35, I'd like to see her after only one."
The reason for such an aggressive approach? The proverbial biological clock. "We need to start preventing miscarriages rather than letting women suffer so many losses," says Hummel. "Every time a woman has a miscarriage, we allow more time to pass, sometimes to the point where she becomes subfertile or even infertile."
Such a proactive stance has led to great advances in the treatment of recurrent miscarriage: Until fairly recently, up to 40 percent of recurrent miscarriages were of unknown origin. Now, Hummel says, the number is less than 5 percent. What's more, he is able to successfully treat the majority of women who seek help for recurrent miscarriage: "Seventy percent of the time, we succeed in helping a woman with chronic miscarriage achieve her goal of having a healthy baby in her arms."
Don't lose hope
For the majority of women who have even one miscarriage, the chances that the next pregnancy will be successful are 80 percent, according to Lerner.
"Information and opportunities for treatment abound," Hummel adds. "We've got the answers and insight needed to take miscarriage out of the category of 'just bad luck.' "