What Causes Miscarriage? An OBGYN Explains.

Let’s make this perfectly clear: Losing a pregnancy is not your fault.

by Isobel Whitcomb
A man comforts his sad wife after a miscarriage, holding her on the couch.

Whether you’ve been trying for a baby for months or received a happy surprise, many expecting parents start to imagine who the bundle of cells growing will turn out to be as soon as those two lines appear on the pregnancy test. The end of that pregnancy means the end of those hopes and expectations, and often leaves couples who experience miscarriage wondering what went wrong. Some blame themselves. But should they? In other words, what causes miscarriage?

The first thing to understand about miscarriage: It’s a common experience. Estimates suggest that anywhere from 10% to 20% of pregnancies end in miscarriage, according to the Mayo Clinic. The actual percentage could be much higher, because many miscarriages happen before a person realizes they’re pregnant.

That is to say, miscarriages are seen by many medical professionals as part of procreation. In fact, between 50% and 75% of miscarriages occur before a person even gets a positive pregnancy test, according to Medical News Today. Miscarriages are a normal part of reproduction, and getting pregnant after a miscarriage is normal — and sometimes even faster and more successful.

What Really Causes Miscarriages

Miscarriage has always been an emotional blame game. But with Roe v. Wade overturned and many states having completely outlawed abortion, miscarriage is a legal risk too. Miscarriages could already lead the person who lost the pregnancy to be arrested in some states via “fetal homicide” and “fetal personhood” laws. But now experts suspect these states to charge people for miscarriage even more frequently.

The vast majority of the time, miscarriages happen due to factors outside the parent’s control, says Martina Badell, M.D., an obstetrician-gynecologist and director of the Emory Perinatal Center. “In general, miscarriages are not caused by things that the mother and father do,” Badell says. Which makes the criminalization of miscarriages even more unjust and scientifically bogus.

Around half of miscarriages occur because the fetus develops with extra or missing chromosomes, according to the American College of Obstetricians and Gynecologists. Typically this happens due to errors that occur due to chance as the embryo or fetus’s cells divide, not due to abnormalities inherited from the parents. In these cases, an embryo often fails to form, even after the egg is fertilized and cells begin to divide — that happens in around one-third of miscarriages that occur less than eight weeks into a pregnancy.

In molar pregnancies, the sperm and egg join incorrectly, forming a non-cancerous tumor instead of a placenta. This tumor is unable to support the fetus the way a placenta does, causing miscarriage.

Less common causes of miscarriage include uncontrolled chronic medical conditions, such as diabetes or thyroid disease, and heavy use of alcohol and cigarettes. Abnormalities in the uterus — such as fibroids, polyps, or a septum, can also cause miscarriage, Badell says.

When Miscarriages Occur

The vast majority of miscarriages happen in the first trimester — and often very early in the first trimester — and don’t signify that an underlying condition was the cause of the miscarriage, Badell says. “Most couples go on to have a healthy next pregnancy.”

However, people who have miscarriages after twelve weeks or experience two consecutive miscarriages should make an appointment with their obstetrician-gynecologist, Badell says. “That’s much more concerning. It might indicate an underlying pathology that we could then treat,” she adds.

Up to 66% of miscarriages that happen after the first trimester are caused by infections, according to a 2016 study published in Human Reproduction Update. There’s some disagreement in the medical field as to which infections cause pregnancy loss, but some studies suggest that chlamydia, toxoplasmosis, HPV, herpes, and hepatitis could lead to miscarriage, the study reported. These infections also account for up to 15% of miscarriages that occur earlier in pregnancy.

It’s just as important for couples to understand what doesn’t cause miscarriage. Intercourse, your daily run, working long hours at the office each day — none of these things will cause you to lose your pregnancy, Badell says.

Taking The Blame Away From Miscarriages

There’s no need for parents to beat themselves up over having drank a glass of wine during pregnancy before experiencing a miscarriage. “One of the really important things is to make sure the couple realizes that in the vast majority of cases, this is not their fault. Dads, too, rack their brain to figure out what they did wrong,” Badell says. “On top of a pregnancy loss, the guilt that they put on themselves is like a second trauma.”