Ten to 25 percent of clinically recognized pregnancies end in miscarriage.
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A miscarriage is the loss of an embryo or fetus before the 20th week of pregnancy. The medical term for miscarriage is spontaneous abortion.
According to the March of Dimes, most miscarriages happen during the first trimester, which is the first 12 weeks of pregnancy. It's rarer for a miscarriage to occur in the second trimester, during the 13th to 19th week.
Most people think miscarriages are very rare, but actually they are remarkably common, said Dr. Zev Williams, director of the program for early and recurrent pregnancy loss at Albert Einstein College of Medicine in New York City, and a miscarriage researcher. "That's one of the big misconceptions about pregnancy loss," he said.
In a study that Williams conducted of more than 1,000 American men and women, over half of the people surveyed thought that a miscarriage was a rare event occurring in fewer than 5 percent of pregnancies. The truth is that 20 to 30 percent of all pregnancies end in miscarriage, Williams told Live Science. That's roughly 1 in every 5 pregnancies, or about 1 million per year in the United States.
The frequency of miscarriages may be even higher than the number reported, because many occur in the very early weeks of pregnancy, before a woman even realizes that she has conceived.
Because miscarriage has traditionally been a taboo subject, women who have experienced one often don't talk about it, and they may end up feeling guilty, ashamed and alone as a result, Williams said. He said that almost every woman he's treated for a miscarriage blames herself for the loss and feels like she did something wrong to cause it.
But it's rarely a woman's fault: The majority of miscarriages — or 60 to 80 percent of them — are due to an abnormal number of chromosomes in the embryo, Williams said.
And yet his research revealed that 76 percent of people surveyed believed that a stressful event often causes a miscarriage, while 64 percent of men and women thought lifting a heavy object played a role in pregnancy loss. But according to Williams, lifting something heavy, regular stress or having an argument at work do not cause miscarriages.
Different types of miscarriage
There are two classes of miscarriage. One class is known as sporadic miscarriage.
Williams said the vast majority of sporadic miscarriages occur because the embryo receives an abnormal number of chromosomes. This genetic glitch happens during fertilization, when the egg and sperm unite, and this makes it difficult for the embryo to grow or survive.
"A woman's body is functioning in a healthy way when it stops the pregnancy," Williams said.
The second class of miscarriage is known as recurrent pregnancy loss. This refers to a woman who has had two or more miscarriages, according to a recently redefined definition by the American Society for Reproductive Medicine. Recurrent pregnancy loss occurs in up to 5 percent of couples attempting to conceive.
Williams said women who have recurrent miscarriages typically have no problem getting pregnant, and they often seem to be having a healthy, normal pregnancy, but they keep miscarrying. To figure out the reason for repeat miscarriages, a woman suffering from the condition needs to undergo testing and see a specialist, who will try to determine a possible cause.
A woman with recurrent pregnancy loss may be evaluated for blood-clotting problems, hormone imbalances, thyroid disorders, autoimmune disease, scarring or fibroids in the uterus. The mother-to-be and her partner may undergo blood tests to evaluate chromosome abnormalities. Still, it's not unusual for no cause to be found, Williams said.
Who is at risk of miscarriage?
Maternal age is by far the biggest risk factor for spontaneous miscarriage, Williams said.
He explained that the older a woman gets, the greater the chances that her eggs might contain an abnormal number of chromosomes, making miscarriages more likely. The risk of miscarriage increases with a mother's age, beginning at age 30 and becoming greater after age 35, according to the National Institute of Child Health and Human Development (NICHD).
Other possible causes of pregnancy loss include the mother's health issues, such as diabetes, high blood pressure, thyroid disease and autoimmune disorders (such as lupus), according to the NICHD. Other factors that may contribute to pregnancy loss may include uterine or cervical abnormalities as well as maternal or fetal infections.
Lifestyle factors, such as a pregnant woman who smokes, drinks alcohol, uses drugs, is obese or has more than 200 milligrams of caffeine (the amount in a 12-ounce cup of coffee) a day, may also increase her risk of miscarriage.
What is a stillbirth?
A stillbirth is when the loss of a fetus occurs after the 20th week of pregnancy. In about half of all cases of stillbirths, no cause was found for the pregnancy loss, according to the NICHD.
Many of the health conditions and lifestyle reasons listed above as possible causes of a miscarriage also apply to a stillbirth. Some additional risk factors for stillbirth include placental problems, umbilical cord accidents, Rh disease (caused by a blood incompatibility between the mother and the fetus) and a lack of oxygen to the fetus during delivery.
What are the warning signs of miscarriage?
The most common symptoms of miscarriage are vaginal bleeding and passing blood clots, according to the American Congress of Obstetricians and Gynecologists (ACOG). A woman may also have cramping that feels worse than menstrual cramps, or mild to severe lower back pain.
Another possible indication of miscarriage is a sudden decrease in pregnancy signs, such as nausea.
Although there are clear symptoms that may suggest a woman has experienced a miscarriage, some of these same symptoms can also occur during a normal pregnancy, Williams said.
How are miscarriages treated?
It is important to keep in mind that most couples who have experienced one or two miscarriages and who have no underlying medical problems typically will go on to have a healthy pregnancy, Williams said.
Miscarriages are usually treated in one of three ways, and each choice has its own risks and benefits, Williams said.
The first approach is to do nothing and for a woman to wait until the pregnancy loss passes naturally on its own. The advantage of this method is that less medical intervention is needed. But one disadvantage is that it can take up to two weeks for the pregnancy loss to occur. Also, bleeding can be very heavy, and important genetic information from the fetal tissue can't be tested to possibly understand why the miscarriage happened.
A second treatment approach is the use of a medication that causes the pregnancy to pass within 6 to 12 hours. The benefit of this treatment is that the timing of the pregnancy loss is known because the cramping can be severe. One disadvantage is that it is hard to recover the fetal tissue to test it afterward.
A third treatment option is a surgical approach known as dilation and curettage, also known as a D&C. In this procedure, a doctor will remove any remaining fetal tissue from the lining of a woman's uterus, and the tissue can be tested. However, there will be bleeding with this approach, and it carries a slight risk of infection or scarring to the uterus.
How long should couples wait before becoming pregnant again following miscarriage?
Williams said that medical thinking on this question has changed over time. It used to be that women were told to wait a year before becoming pregnant again following a miscarriage; then it became six months, and now it's three months, he said.
A lot depends on when the miscarriage took place during the pregnancy, Williams said. If the pregnancy loss happened in the early weeks of pregnancy, a couple can wait one menstrual cycle, he advised. (Most women get their period again four to six weeks after a miscarriage, according to the March of Dimes.) But if it occurred after 20 weeks, he suggested waiting at least three months.
Williams recommended that after a miscarriage, a woman should be monitored by her physician or midwife, and she should ideally wait for her uterus and hormone levels to return to their prepregnancy states.
It's important for her human chorionic gonadotropin (hCG) levels to return to zero, he said. That's because if a woman who has miscarried has fluctuating levels of hCG in her blood and tries to conceive too soon, it's hard to know if her levels of the so-called pregnancy hormone are elevated as a result of fetal tissue from the old pregnancy or because of a new one.
- ACOG: Early Pregnancy Loss (Miscarriage)
- NICHD: Pregnancy Loss: Overview
- ASRM: What Is Recurrent Pregnancy Loss (RPL)?