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.