Miscarriage Demystified

Pregnancy losses are common and usually unavoidable. The good news is that most women go on to have healthy babies.


For many women, the instant exultation that a positive pregnancy test evokes is slowly replaced with a nagging fear: What if something goes wrong? What if I lose the baby? While a certain number of pregnancies do, sadly, end in miscarriage, it’s reassuring to know that the majority of pregnancies result in healthy babies. And even if a woman does suffer a loss, she’s very likely to have a healthy pregnancy in the future.

If you experience a miscarriage, you may feel very alone. The fact is, you actually have plenty of company: Studies reveal that anywhere from 10 percent to 25 percent of recognized pregnancies end in miscarriage. But many women keep miscarriages secret, even from close friends and family members, often because they feel guilty or ashamed. Those emotions are unwarranted. “The routine miscarriages many women have are due to pure bad luck,” says Henry Lerner, M.D., an OB-GYN at Newton-Wellesley Hospital in Newton, Mass., and an assistant clinical professor in obstetrics and gynecology at Harvard Medical School. “Since they’re random, they’re not likely to occur the next time around.” In fact, for the majority of women who have a miscarriage, the chances of a successful next pregnancy are 80 percent, Lerner adds.

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. “Even a typical car accident or fall won’t cause one.” However, a Swedish study found that pregnant women who were exposed to secondhand smoke were 67 percent more likely to miscarry than those who weren’t exposed.

Certain health conditions also predispose some women to miscarriages. Thyroid problems, diabetes, genital-tract infections, and being either underweight or obese can all pose some degree of risk. That’s why it’s important to try to get such conditions under control before you conceive. And though many women believe stress can cause a miscarriage, scant research supports this. “I know of no firm evidence linking stress to miscarriage,” Lerner says. Some infections, such as listeriosis (most often caused by eating undercooked meat or unpasteurized dairy products) and toxoplasmosis (usually caused by eating raw or undercooked meat or by contact with cat feces), can also cause pregnancy loss, but luckily these are rare.

That said, here’s an in-depth look at why most miscarriages happen, along with news about the latest research into the causes and the treatments being offered.

When chromosomes are the problem
The main causes of miscarriage fall into two broad categories: problems with the embryo or fetus and problems 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 Lerner, who is also the author of Miscarriage: Why It Happens and How Best to Reduce Your Risks (Perseus). “But sometimes they get scrambled. Since chromosomes are the blueprint for development, if they’re paired incorrectly, the embryo stops developing 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 takes place—never make it to the point that a woman would have a positive pregnancy test.

“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.” Most miscarriages 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.

The role of age
Closely tied to the incidence of chromosomal abnormalities in pregnancy is a woman’s age. “The likelihood of miscarriage increases exponentially as a woman gets older,” says Lesley Regan, M.D., 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. Risk increases to 30 percent at age 40 and to nearly 40 percent if she is 42 or older.

“At birth, a woman has all the eggs she’ll ever have,” Lerner explains. “The older she gets, the more time there is for her eggs to be damaged by such environmental insults as noxious chemicals, gases and heavy metals. This inevitable DNA deterioration over time could make the eggs’ instructions for growth unreadable.” Scientists now suspect that the father’s age—particularly if he is older than 40—may also be a factor in miscarriage, although a much smaller one than the mother’s.

Anatomical abnormalities
The second most common cause of early losses are abnormalities in a woman’s body—most often her uterus, according to Hummel. “At least 30 percent of all miscarriages are due to anatomical factors within the uterus,” he explains. “Of these, fibroids are the biggest problem.”

Hummel points out that although these noncancerous tumors are extremely common in women of reproductive age, not all contribute to miscarriage. “The key is its location and size,” he says. The closer a fibroid is to the center of the uterus, where a fertilized egg is likely to implant, the more likely it is to cause a miscarriage; as for size, any fibroid larger 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 without hampering her ability to conceive or carry a pregnancy to term, Hummel adds.

If you think you’re miscarrying
Unfortunately, there’s nothing you can do to stop a miscarriage once it starts. Nor should you want to, as the majority of losses are due to serious problems with the embryo or fetus.

The hallmarks of a miscarriage include heavy bleeding and cramping, as opposed to normal spotting, which occurs frequently in early pregnancy. This lighter spotting can be caused by implantation of the fertilized egg or by the developing placenta “digging” its roots into the wall and blood vessels of the uterus. “But half of the time, bleeding does indicate a miscarriage,” says 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 or midwife. If you have in fact miscarried, she will want to make sure your body has completely expelled the tissue. If it hasn’t, you may need a procedure called a D&C to remove it. Coping with a loss A recent study found that women often suffer depression or anxiety for several years after a miscarriage.

If you need help, visit fitpregnancy.com/miscarriage for resources.