Reasons for Miscarriage

Why First-Trimester Miscarriages Happen

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Reasons for miscarriage. JGI/Tom Grill / Getty Images

The reasons for miscarriage aren't always known. In fact, more often than not, you will simply not know what caused a specific miscarriage. The following are some possible explanations for why a single first-trimester miscarriage might occur in someone without a history of miscarriage. (Causes of recurrent miscarriages are more complex.)

Chromosomal Abnormalities in the Baby

Certain errors in the chromosomes of the developing baby are incompatible with life and lead to miscarriage. This is suspected to be the explanation behind the vast majority of first-trimester miscarriages, especially in women without a history of miscarriage. According to the American College of Obstetricians and Gynecologists, this is due to the embryo having an abnormal number of chromosomes.

Moms over 35 are probably more likely to miscarry for this reason. Most women who have pregnancies affected by chromosomal abnormalities will have normal subsequent pregnancies.

Infections or Food Poisoning

Some types of viral and bacterial infections can lead to miscarriage or stillbirth. Infections generally pose a higher risk of pregnancy loss in the second trimester and later, but a few can cause problems in the first trimester also.

No Known Reason

Sometimes even when the doctor tests for chromosomal abnormalities in the lost pregnancy, the results come back normal. It can be very hard to cope with having no answer for why a miscarriage occurred, and you may be tempted to blame yourself. But miscarriage is almost never anyone's fault.

Underlying Health Problems

Sometimes underlying chronic health conditions, such as diabetes or celiac disease, in the mother can lead to an unexpected miscarriage. Most of the time, however, detecting and treating that condition should lead to a normal subsequent pregnancy. Other times, multiple miscarriages may occur because of antiphospholipid syndrome or another known recurrent miscarriage cause.

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  1. American Pregnancy Association. Miscarriage. Updated October 10, 2019.

  2. American College of Obstetricians and Gynecologists. Early Pregnancy Loss. Updated August 2015.

  3. Hardy K, Hardy PJ. 1(st) trimester miscarriage: four decades of studyTransl Pediatr. 2015;4(2):189–200. doi:10.3978/j.issn.2224-4336.2015.03.05

  4. Tersigni C, Castellani R, Waure CD, et al. Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanismsHuman Reproduction Update. 2014;20(4):582-593. doi:10.1093/humupd/dmu007.

  5. Di Prima FA, Valenti O, Hyseni E, et al. Antiphospholipid Syndrome during pregnancy: the state of the artJ Prenat Med. 2011;5(2):41–53.