Miscarriage and Stillbirth Causes

There Are a Few Known Causes for Pregnancy Loss, but Many Questions Still Remain

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Why did I have a miscarriage? Or a stillbirth? 

After a pregnancy loss, most couples want answers. Many people wonder if the loss happened because of something they did - or if the miscarriage or stillbirth could have been prevented somehow. Usually, the answer to that question is no. Miscarriage and stillbirth is rarely anyone's fault, and sometimes pregnancy loss is even a predetermined outcome at the time of conception.

Even though we know pregnancy loss usually does not happen because of anything the mother (or father) did, doctors cannot always explain why they do happen. Aside from a few known miscarriage and stillbirth causes, there are many theories and plenty of ongoing research and controversy.

What Causes a First Miscarriage?

Sporadic, one-time pregnancy losses are usually caused by random chromosomal abnormalities in the developing baby. The medical community widely recognizes this explanation. In many cases, doctors assume this as the default explanation for first time miscarriages - with good reason, given that most couples go on to have a normal pregnancy after one miscarriage.

In most cases, a pregnancy lost to miscarriage has a problem in the chromosomes, such as extra chromosomes or missing chromosomes that cause the pregnancy to stop developing and eventually be miscarried. Because chromosomal flaws are usually random, one-time events, most doctors do not initiate testing for miscarriage causes after the first miscarriage.

Anyone can have a miscarriage due to chromosomal flaws, regardless of age, but the highest risk for this particular problem is in mothers over 35.

What Causes Recurrent Miscarriages?

Two miscarriages in a row qualifies as recurrent miscarriages - and the cause is less likely to be two random chromosomal errors in a row.

After the second loss, most doctors will start the process of testing for recurrent miscarriage causes because the odds are higher that the woman may have a detectable problem causing the losses.

About half the time, doctors can find a cause for recurrent miscarriages and the woman can be treated in her next pregnancy. The other half of the time, tests do not reveal a cause. But even with two unexplained miscarriages, a woman can get pregnant again and still have greater statistical odds of a normal pregnancy than another loss.

In recurrent miscarriages, causes are much more controversial than in single miscarriages. Some doctors will test for and treat particular problems while others will not. Widely recognized causes of recurrent miscarriages include the following:

Many doctors feel that low progesterone and other hormonal imbalances may cause recurrent miscarriages.

Treatment with progesterone supplements is fairly common after one or two miscarriages, but not all medical practitioners agree on the practice.

Some practitioners also feel that immune system malfunctions, such as high levels of natural killer cells, may be a culprit in some women, but others dispute this view.

What Causes Stillbirth and Infant Loss at Birth?

Stillbirths (losses after the 20th week) and premature births usually have different causes from earlier miscarriages, although chromosomal errors in the baby can cause stillbirths.

The most common causes of stillbirth and very early preterm labor are cervical insufficiency, problems in the placenta and preterm labor due to medical issues in the mother.

Support After a Miscarriage or Stillbirth

Your doctor should be able to give you information on whether you need testing for pregnancy loss risk factors and causes. Regardless of the cause, if you have had a miscarriage or a stillbirth, be sure to seek out emotional support from friends and relatives or look for support groups if you don't have an adequate support structure. You should not have to go through this alone. 


Repeated Miscarriage. American College of Obstetricians and Gynecologists. September 2005.

Check, J.H, Weiss, R.M. and Lurie, D. (1992). Analysis of serum human chorionic gonadotrophin levels in normal singleton, multiple and abnormal pregnancies. Human Reproduction.

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