Miscarriage tops the list of many pregnant women's fears, but experts are making big strides toward understanding it.
When I found out I was pregnant, I was simultaneously thrilled about having a baby and petrified that something would go wrong. Chalk it up to the occupational hazards of being a health writer, too much time spent trolling the Internet or a somewhat obsessive, glass-half-full-of-water-that-might-contain-toxins personality. Whatever the reason, I had a long list of bad things in my head. And miscarriage topped the list.
So I fretted. I worried. I ate spinach by the boatload and downed fistfuls of folic acid, all the while trying not to fall in love with the little bundle of cells dividing within me--because sometimes, I knew, they just don't make it. But mine did. And I've got a strapping 9-year-old son to prove it.
If you're like many pregnant women, the prospect of miscarriage looms high on the what-if list, as it did for me. But you can take comfort in the fact that while a certain number of pregnancies do end early, the vast majority result in healthy babies. Here's a look at why miscarriages happen, along with reassuring news about why your chances of having one might be lower than you think.
When chromosomes are the problem
The four main causes of miscarriage include problems with the embryo or fetus, and anatomical, hormonal and blood-clotting abnormalities within the mother. More than 50 percent result from the first--what experts refer to as "chromosomal errors."
"When the chromosomes of the egg and those of the sperm fuse to form an embryo, they usually pair up correctly," explains Henry Lerner, M.D., an OB-GYN at Newton-Wellesley Hospital in Newton, Mass., and a clinical instructor in obstetrics and gynecology at Harvard Medical School in Boston. "But sometimes they get scrambled. Since chromosomes are the blueprint for development, if they're paired incorrectly, the embryo stops developing at some point and dies."
These errors can be so significant that pregnancy per se never occurs--the fertilized egg may begin to divide and grow but fails to implant itself in the uterus. In fact, it's estimated that as many as half of clinical pregnancies--those in which fertilization does take place--never make it.
"The great majority of genetically abnormal embryos don't implant, and of the few that do, most miscarry early on," says William P. Hummel, M.D., a reproductive endocrinologist specializing in miscarriage and infertility at San Diego Fertility Center. "The body recognizes a problem and takes care of it before a woman even knows she's pregnant." From there, most miscarriages will happen within the first 12 weeks. "Once you pass the eight- to 12-week mark and we see the fetus's heartbeat by ultrasound, you have a 98 percent chance of having a full-term, healthy baby," Hummel adds.
Problems within the mother
Abnormalities in a woman's body--most often, her uterus--are the next most common cause of early losses, according to Hummel. "At least 30 percent of all miscarriages are due to anatomical factors within the uterus," he explains. "Of these, uterine fibroids are the biggest problem."
Hummel points out that although fibroids-noncancerous tumors are extremely common in women of reproductive age, not all result in miscarriages. "The key to a fibroid causing a miscarriage is its location and size," he says. The closer it is to the center of the uterus, where a fertilized egg is likely to implant, the more likely it is to cause problems; as for size, any fibroid greater than 5 centimeters (about 2 inches) can be problematic. Surgery to remove the fibroid is often extremely effective in reducing a woman's risk of miscarriage, Hummel adds.
The third most likely cause is hormonal. "Ten percent of miscarriages are related to hormonal events, particularly low progesterone levels," Hummel says. "Progesterone advises a woman's body to accept a foreign embryo as something desirable: It's nature's immunosuppressant." If a woman has low levels of this hormone, using progesterone supplements until eight to 10 weeks' gestation, when the placenta takes over the job of manufacturing it, dramatically increases the chances of a healthy outcome.
The fourth significant contributor to miscarriage is a relatively new discovery called thrombophilias, or blood-clotting disorders within the mother. "For women with thrombophilias, blood clots form in the smallest, most fragile blood vessels: those in the fetus, in the placenta and in the umbilical cord," Hummel explains. "These clots can impede blood flow and cause the fetus to die." Anti-coagulant treatments such as low-dose aspirin and heparin administered throughout pregnancy help prevent clotting and reduce the risk of miscarriage.
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.' "
The hallmarks of a miscarriage include heavy bleeding and cramping, as opposed to normal spotting, which occurs frequently in early pregnancy. This spotting can be caused by implantation or by the placenta "digging" its roots into the wall of the uterus. "But half the time, bleeding does indicate a miscarriage," says OB-GYN Henry Lerner, M.D. "It's a result of the fetus having died and the tissue starting to disintegrate. By the time you start bleeding, it's already done--it usually takes seven to 10 days to see any bleeding."
If you think you might be miscarrying, call your doctor. If you have in fact miscarried, he will want to make sure your body has completely expelled the tissue. If it hasn't, you may need a D and C, a minor surgical procedure, to remove it.
Later Miscarriage: What Are The Chances?
Occurring in less than 2 percent of pregnancies, miscarriages after the first trimester are most often caused by chromosomal abnormalities that "slip through," certain rarer hereditary chromosomal disorders that don't cause fetal death until late in pregnancy, or a so-called incompetent cervix. This is a condition in which the cervix cannot support a growing fetus; the weakening may be caused by previous surgery (such as for a precancerous condition) or by trauma from a previous delivery. It also can be congenital, says miscarriage expert Henry Lerner, M.D. Whatever the cause, a miscarriage resulting from an incompetent cervix usually occurs between 12 and 24 weeks of pregnancy. If you're diagnosed with cervical incompetence--and only about 1 in 500 women are--a small stitch may be inserted in your cervix to help keep it closed until delivery.