Seven Most Common Miscarriage Causes

A few months after my first child was born, I wanted to be pregnant again—as soon as possible. I wanted my children to be close in age, the closer the better, and when my son was 13 months old, I got my wish and discovered I was pregnant.

But before I even had a chance to share the news with my husband (he was traveling out of the country), I miscarried. I was only five weeks pregnant. Truth be told if we hadn’t been trying to conceive, I probably wouldn’t have even noticed that my period was late—and so I was surprised by how sharply I felt the loss. My obstetrician’s observations that I was in good company—that around 15 percent of “known” pregnancies (i.e., pregnancies confirmed with a test), and up to half of all pregnancies end in miscarriage during the first trimester—didn’t soothe my sadness. Nor did his assurance that the miscarriage wasn’t caused by something I had done, or hadn’t done, that it was “just one of those things.” But I was comforted when I considered the other statistic: that most of the time miscarriage is a one-time occurrence.

If you have had a miscarriage, chances are you want to know what caused it, and what you can do to prevent it from happening again. For starters, relax. “Since you got pregnant once, the odds are 80 percent that you will go on to have a healthy baby, and as many healthy babies after that as you want,” says Henry Lerner, MD, clinical professor of obstetrics and gynecology at Harvard Medical School and author of Miscarriage: Why it Happens and How Best to Reduce Your Risks (Perseus Book Group, 2003). Next, accept that you may never know why you miscarried. “The majority of the time miscarriage is a random, isolated event and we can’t pinpoint a cause,” he says. Women who go on to have two or three miscarriages (called recurrent miscarriage) may ultimately learn they have a medical problem that is causing their pregnancies to end spontaneously, but even with recurrent miscarriage, half the time there is no known cause.

Like most women who lose a pregnancy, I will never know why I miscarried, but I did get pregnant again, about two months later. My second baby was born two weeks after her brother’s second birthday. They are, as it turns out, close enough.

Here's a look at the most common causes of both single and recurrent miscarriage.

Miscarriage Cause: Chromosomal Abnormalities

Why it Leads to Miscarriage
“Mismatched chromosomes account for at least 60 percent of miscarriages,” says Bryan Cowan, MD, chair of the department of obstetrics and gynecology at the University of Mississippi Medical Center in Jackson, and a spokesperson for the American College of Obstetricians and Gynecologists. Chromosomes are the tiny structures in each cell that carry our genes; we each have 23 pairs of them, one set from our mother and one set from our father. Sometimes, when the egg and sperm meet, one or the other is faulty and then the chromosomes can’t line up properly. In that case, the resulting embryo has a chromosomal abnormality and the pregnancy usually results in a miscarriage. Couples who experience two or more miscarriages in a row sometimes learn, through medical testing, that they have chromosomal anomalies that don’t affect them, but do prevent a pregnancy from taking hold.

What You Can Do
If you have one miscarriage, be patient. The odds are strongly in your favor that you will get pregnant again and deliver a healthy baby. If you miscarry again, however, consider preserving the tissue you pass (if possible, save it in a sterile saline contact-lens solution) and take it to your physician to be sent to a lab for chromosomal testing. “If it’s chromosomally normal, we can immediately start looking for other issues that may be responsible for the miscarriages and may be treatable,” says Jonathan Scher, MD a fertility specialist in Manhattan and co-author of Preventing Miscarriage: The Good News (Collins 2005).