If you’ve had a miscarriage, you’re not alone. Miscarriage is, by far, the most common complication of pregnancy: 1 in 4 pregnancies result in miscarriage. That’s more than 1 million miscarriages annually in the U.S. For many women and couples who suffer from one or more miscarriages, a big question is: Why did this happen to me?

Before we answer that, let’s go over some of the reasons why the miscarriage did not happen. Miscarriage is often a very difficult experience both emotionally and physically. Misconceptions that many women and couples carry with them can sometimes make the experience much more difficult. It is important to know that the miscarriage did not occur because of stress at work, or because you got into an argument with your spouse or lifted something heavy. The miscarriage did not occur because you second-guessed whether you wanted to have a baby or went for a long walk. In a study we conducted of more than 1,000 adults across the U.S., these were commonly believed causes of miscarriage, and these misconceptions often lead to unwarranted feelings of self-blame and guilt.

So why do miscarriages occur? When a woman has one or two miscarriages, it’s usually because the fetus has the wrong number of chromosomes, the genetic material that tells our cells what to do. Normally, we inherit 23 chromosomes from each parent, resulting in a normal number of 46 chromosomes. Sometimes the fetus can have too many or too few chromosomes, and this is almost always incompatible with life. The mistake leading to having too many or too few chromosomes occurs at the time when the egg or sperm or early embryo are forming. In these cases, the miscarriage is really the result of the woman’s body acting in a healthy manner and recognizing that the pregnancy is not destined to become a healthy baby and stopping the pregnancy early. Genetic testing of placenta after a miscarriage can confirm this diagnosis.

Recurrent miscarriage is when a when a woman has three or more miscarriages. In cases of recurrent miscarriage, the causes can be much more complex and challenging to determine. For a pregnancy to successfully carry to term, a tremendous number of systems in the body have to work properly. For example, the uterus has to have the proper structure; fibroids, polyps or having a wall in the middle of the uterus (known as a septum) can all be causes of miscarriages. Hormone levels have to be correctly regulated; problems such as diabetes or thyroid disease can cause miscarriages. Blood cannot clot too much or too little as either can make miscarriages more likely.

The mother’s immune system plays an important role in pregnancy, and improper functioning of the mother’s immune system likely plays a role in some cases of recurrent miscarriage. In pregnancy, the mother’s immune system has to “tolerate” the fetus and avoid rejection. However, our understanding of how the immune system accomplishes this is still in the early stages, and blood tests to diagnose improper functioning of the immune system have not held-up to rigorous investigation. Many empiric therapies have been tried in an effort to correct an immune defect, such as steroids, intralipid or IVIg (intravenous administration of antibodies), but these have been shown to be largely ineffective or even harmful. Recently, use of medications to actually boost the immune system — and induce tolerance — has shown promise, but additional studies are ongoing.

Finally, in up to half of all cases of miscarriage, no underlying cause is found. We and other groups are working to discover other reasons for miscarriage so that the cause can be identified and treated in order to prevent them in the future, but this work is still in the earliest stages. While there can be a terrible sense of loss and sadness after a miscarriage, for most women and couples who have a miscarriage, they can rest assured that they do have a very high likelihood of ultimately having a healthy baby.

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Miscarriage: No One’s Fault originally appeared on usnews.com