When Do Most Miscarriages Happen?

The first 12 weeks have the highest pregnancy loss rate.

pregnant woman gets ultrasound
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Pregnancy is obviously a time of anxiety as well as anticipation, and a lot of pregnant women worry, especially those who have had a miscarriage before. Some seek comfort in statistics, feeling a greater sense of relief after passing specific milestones in pregnancy at which statistical odds of miscarriage decrease.

So at what point in pregnancy will you be able to breathe a sigh of relief and stop worrying so much about having a miscarriage?

Definition of Miscarriage

An early pregnancy loss is a pregnancy loss or miscarriage before the 13th week of gestation (during the first trimester). Pregnancy losses that occur between 13 and 19 weeks gestation are called second trimester pregnancy losses or second trimester miscarriages. A pregnancy loss at 20 weeks or greater gestation is not called a miscarriage, but a stillbirth—where the fetus dies in the mother's uterus.

When Do Miscarriages Most Commonly Occur?

According to the American College of Obstetricians and Gynecologists, approximately 80 percent of miscarriages happen within the first trimester. As pregnancy progresses, miscarriage risk decreases. In addition, your risk of miscarriage drops significantly after a doctor detects a heartbeat on ultrasound.

How Common Are Miscarriages?

If you're wondering when miscarriages occur, you may also have questions about how common miscarriages are.

The good news is that by the time you actually get a positive pregnancy test, your risk of miscarriage will be at the lower end of that range.

In an older study in the New England Journal of Medicine, researchers followed 221 women over a combined total of 707 menstrual cycles, with 198 total pregnancies.

They found that 22 percent of the pregnancies ended before they could be detected clinically (such as by standard urine pregnancy tests). Including the early miscarriages, the total miscarriage rate was 31 percent. 

Current evidence backs up this older study, suggesting that anywhere between 10 and 20 percent of recognized pregnancies will end in miscarriage and 30 to 40 percent of all conceptions end in miscarriage. 

While early pregnancy loss occurs in about 10 percent of all recognized pregnancies, second trimester miscarriages occur in about 1 to 5 percent of pregnancies. Stillbirth occurs in about 0.3 percent of pregnancies.

What Causes Miscarriage?

About half of miscarriages are caused by chromosomal abnormalities, making these problems the single most common miscarriage cause. Most of these are random one-time occurrences that are not inherited from the parents. 

The earlier in pregnancy a miscarriage occurs, the more likely it was caused by a chromosomal abnormality. 

Usually, these abnormalities are aneuploidies, meaning there is an incorrect number of chromosomes, either an extra chromosome (as in the case of Trisomy 21 or Down Syndrome) or a missing chromosome.

The biggest miscarriage risk factor is a mother's age.

According to the American College of Obstetrics and Gynecologists, the number of miscarriages in the first trimester for women increases dramatically as a woman ages. Here are the statistics showing this rise:

  • age 20 to 30 years: 9 to 17 percent miscarriage rate
  • age 35 years: 20 percent miscarriage rate
  • age 40 years: 40 percent miscarriage rate
  • age 45 years: 80 percent miscarriage rate

A Word From Verywell

If you have experienced a miscarriage in the past, worry you may have one, or both, please know that you are not alone. That being said, if your worry is persistent and affecting how you feel and function, be sure to seek guidance from your doctor.

There are a number of therapies available that can help you feel better.

Sources:

The American College of Obstetricians and Gynecologists. (May 2015). Practice Bulletin: Early Pregnancy Loss. 

Michels TC, Tiu AY. Second trimester pregnancy loss. Am Fam Physician. 2007 Nov 1;76(9):1341-46.

Tulandi T, Al-Fozan HM. Spontaneous abortion: (December 2016). Risk factors, etiology, clinical manifestations, and diagnostic evaluation. In: UpToDate, Levine D, Barbieri RL (Ed), UpToDate, Waltham, MA. 

Tulandi T. (December 2016). Patient education: Miscarriage (Beyond the Basics). In: UpToDate, Barbieri RL (Ed), UpToDate, Waltham, MA. 

Wilcox et al. Incidence of early loss of pregnancy. N Engl J Med. 1988 Jul 28;319(4):189-94.

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