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The Secret Loss

What causes miscarriage, what doesn’t

Illustration: Philippe Weisbecker

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For most women, pregnancy is a time of happy expectation. But for others — perhaps many more than we realize — hope gives way to despair when the pregnancy is lost.
    Unfortunately, miscarriage is a fairly common event, which can plague a woman and her partner with feelings of sadness, loss and guilt. As frequently as it happens, however, miscarriage still often occurs for no known reason. Thankfully, though, science has recently made new strides in targeting some of the causes.

Causes of miscarriage
The American College of Obstetricians and Gynecologists estimates that 15 to 20 percent of pregnancies end in miscarriage in the first or early second trimester, but that statistic doesn’t include miscarriages that occur before a pregnancy is even suspected. (Some experts put the actual miscarriage rate — for all pregnancies — at 50 to 75 percent.) Well over half of the miscarriages that occur in the first 13 weeks of pregnancy are the result of chromosomal abnormalities — random genetic errors that result in nonviable pregnancies. These types of miscarriages can’t be anticipated, treated or prevented — the genetic material needed for a healthy fetus to develop is simply missing. (See “What Doesn’t Cause Miscarriage” on page 50.)
    However, certain lifestyle choices have been tied to higher rates of miscarriage. Smoking cigarettes, drinking too much alcohol, consuming more than three cups of coffee a day or taking street drugs can decrease a pregnant woman’s chances of successfully carrying a baby to term.
Those who put off pregnancy until later in life may face challenges, also; as women age, their eggs do not divide as well, which increases the chance of chromosomal abnormalities in the eggs. Miscarriage rates and birth defects are significantly higher in women older than 35. 

Getting help
Women who miscarry three or more consecutive times are said to suffer recurrent pregnancy loss; after two miscarriages, a woman may want to seek help from a specialist.
    When miscarriages repeatedly occur in the second trimester (between 14 and 26 weeks) of pregnancy, the cause is likely to be anatomic — due to an abnormally shaped uterus or an “incompetent cervix” (one too weak to support the increased pressure of a growing fetus). Women with such a condition may want to consider corrective surgery; the majority of women diagnosed with incompetent cervixes can be helped with a surgical stitch that helps keep the cervix closed until delivery, as well as bed rest.
    Finding the cause for repeated first-trimester miscarriages can be trickier. Although in most cases early miscarriages are caused by random chromosomal abnormalities, hormones may also play a role in early pregnancy losses. For example, women who suffer repeated first-trimester miscarriages may not be producing enough progesterone, a hormone that is critical for sustaining pregnancy. When a pregnant woman fails to produce enough progesterone, the diagnosis is luteal phase defect, or LPD. Although it may take two or three miscarriages to diagnose, LPD is easily treated with progesterone supplementation.
    In the past two decades, experts have come to believe that some recurrent miscarriages may be due to problems with a woman’s immune system. More controversial is the idea that some women may fail to produce the protective antibodies that keep their bodies from rejecting a developing fetus. Treatment for this condition is in experimental stages.

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