What Causes Recurrent Miscarriage?

Recurrent miscarriages aren't common, but scientists might have found the reason behind them. Here's what expectant parents need to know.

Stem cell research, scientist holding a culture jar with a DNA gel in the background
Stem cell research, scientist holding a culture jar with a DNA gel in the background. Photo: Getty Images

Experiencing one miscarriage is devastating enough, but some women lose pregnancies again and again. And while it's easy to blame yourself for recurrent miscarriages, they're likely random events outside of your control. Find out more about recurrent miscarriage causes, and learn why they might be happening to you.

How Common Are Multiple Miscarriages?

According to the American College of Obstetricians and Gynecologists (ACOG), about 15 to 20 percent of known pregnancies end in miscarriage. About 70% of first trimester miscarriages—and 20% of second trimester miscarriages—stem from a chromosomal abnormality affecting the fetus's genes. Other causes might include hormonal imbalances, uterine problems, maternal health conditions, and excessive drug and alcohol use.

Since the majority of miscarriages are completely random, having one usually does not increase your odds for another. In fact, for the majority of women who have a miscarriage, the chances of a successful next pregnancy are 80 percent. Your chance of miscarrying again will also remain the same—about 15 percent for women under 35.

Your risk of having a third miscarriage increases slightly, but the difference is still minimal. "After two miscarriages in a row, your risk does go up, but most doctors won't start testing for genetic, uterine, or hormonal problems until you've had three," says Jonathan Schaffir, M.D., an assistant professor of obstetrics and gynecology at Ohio State University College of Medicine.

It's important to note that only one in 100 women trying to conceive suffer three or more consecutive pregnancy losses.

Recurrent Miscarriage Testing and Treatment

If you have multiple miscarriages, you should visit your healthcare provider. He will likely conduct physical and pelvic exams, as well as evaluate your past medical history. Other tests may be given on an as-needed basis; they may include ultrasounds, hormonal tests, endometrial biopsies, genetic testing, blood tests, and more.

If the doctor finds an underlying cause for recurrent miscarriages, which happens in the minority of cases, he will treat it appropriately. For example, the woman can undergo surgery for anatomical issues, or she might try controling health problems like diabetes and thyroid disorders.

What Causes Recurrent Miscarriage?

Medical experts haven't been able to make a connection as to why some women experience multiple miscarriages, but researchers from the University of Warwick think they have the answer.

Professor Jan Brosens and his team discovered that a lack of stem cells in the womb lining is likely responsible for miscarriages in "thousands" of women. "We have discovered that the lining of the womb in the recurrent miscarriage patients we studied is already defective before pregnancy," the professor of obstetrics and gynecology wrote in the study, published in the journal Stem Cells in February 2016.

For the study, Brosens and his team studied tissue samples from the womb linings donated by 183 women being treated at the Implantation Research Clinic, University Hospitals Coventry and Warwickshire NHS Trust. They found that an "epigenetic signature" common with stem cells was missing from the tissues of women who have suffered more than one miscarriage.

The team also found that a lack of stem cells increases the aging rate of cells in the womb. The uterus relies on stem cells to regenerate after menstruation, pregnancy, and miscarriage; the lack of those cells—and the aging process—creates an inflammatory response that affects the ability for a fetus to grow to full term.

"After an embryo has implanted, the lining of the uterus develops into a specialized structure called the decidua, and this process can be replicated when cells from the uterus are cultured in the lab," wrote Brosens. "Cultured cells from women who had had three or more consecutive miscarriages showed that aging cells in the lining of the womb don't have the ability to prepare adequately for pregnancy."

In other words, the body can't fully renew itself to make a welcoming environment for a baby.

While this recurrent miscarriage testing paints a bleak picture, there is hope. The team believes that this discovery will lead to treatments that will stimulate the function of stem cells in women without them—and they're already working on new interventions.

"Our focus will be two-fold," said Siobhan Quenby, study co-author and University of Warwick Professor of Obstetrics. First, they'll work to improve how at-risk women are screened through new endometrial tests. "Second, there are a number of drugs and other interventions, such as endometrial 'scratch', a procedure used to help embryos implant more successfully, that have the potential to increase the stem cell populations in the womb lining."

Added Brosens: "I can envisage that we will be able to correct these defects before the patient tries to achieve another pregnancy. In fact, this may be the only way to really prevent miscarriages in these cases."

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