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Common Chromosomal Abnormalities That Can Cause Miscarriage

Courtesy of Caroline Wurtzel/Romper

Miscarriage is an incredibly common experience that people don’t often talk about. But pregnancy loss, particularly in early pregnancy, is not uncommon, and the majority of these miscarriages are caused by chromosomal abnormalities. Many people wait until after 12 weeks to tell anyone they’re pregnant so they don’t have to deal with the disappointment, grief, and platitudes from well-meaning friends in a public way, which can sometimes make the experience seem very lonely.

According to the American Pregnancy Association’s website, 10 to 25 percent of pregnancies will end in miscarriage. Additionally, chromosomal abnormalities account for at least 60 percent of those losses, 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, told Parenting.

A chromosomal abnormality essentially means that something is not right with the zygote’s chromosomes, causing the fertilized egg not to implant at all, or causing the pregnant person’s immune system to terminate the pregnancy. “Most chromosomal abnormalities are the cause of a damaged egg or sperm cell, or are due to a problem at the time that the zygote went through the division process,” according to the American Pregnancy Association. There are two main types of chromosomal abnormality induced pregnancy loss, according to a chapter by Joe Leigh Simpson, MD and Sandra Ann Carson, MD in the Global Library of Women’s Medicine.

Preimplantation Losses

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Preimplantation losses are what they sound like — a fertilized egg fails to implant in the uterine lining due to chromosomal abnormalities. According to Simpson and Carson, approximately half of morphologically normal embryos that resulted from IVF in women with a mean age of 35 to 37 years old show abnormalities, and if the embryos are morphologically abnormal, there's a higher rate of abnormalities (more than 50 percent). Based on this, they conclude that “overall perhaps one-third of [chromosomally abnormal embryos] present at day three fail to persist to day five, when implantation occurs.”

In these cases, you may not even be aware that you had conceived at all, as bleeding may occur right around the time of your expected period.

Numerical Chromosomal Abnormalities

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Simpson and Carson call numerical chromosomal abnormalities “the most frequent causes of early pregnancy loss.” Chromosomal abnormalities can cause loss at any stage of pregnancy, but are most likely in the first trimester and become less likely the longer the pregnancy goes on.

There are a variety of chromosomal abnormalities that can cause loss, with autosomal trisomy being the most common, and which Simpson and Carson say account for 25 percent of miscarriages caused by these abnormalities. In these cases, the embryo has three instances of a particular chromosome, instead of the usual two.

What Next?

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If you think you may be miscarrying, it’s important to talk to your doctor. In some cases, your uterus doesn’t completely empty itself out and you may need medical intervention. Regardless, it’s a good idea to have your healthcare provider take a look and ensure that everything is OK.

Ultimately, you may never know why your pregnancy terminated itself, but the very likely reason is because something was wrong, and your body was protected you and your unborn child by ending a non-viable pregnancy. This, of course, does not make pregnancy loss any easier, particularly when it is a wanted pregnancy.

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, told Parenting that if a person gets pregnant and then miscarries, “the odds are 80 percent that you will go on to have a healthy baby.”

And while miscarriages are incredibly common, the fact that they’re not often talked about, can make it feel like a lonely and isolating experience. But you’re absolutely not alone, and finding support and allowing yourself time to mourn is crucial and critical. It’s perfectly normal to grieve; losing a pregnancy is never easy. Don’t be afraid to take care of yourself in the way that feels safest for you, and to honor your experience in whatever way you need to.