Chance of Miscarriage by Week: Full Chart

This article is an excerpt from the Shortform summary of "Expecting Better" by Emily Oster. Shortform has the world's best summaries of books you should be reading.

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A minority of pregnancies end in miscarriage, and there’s largely nothing you can do about it. About 90% of miscarriages in the first trimester are due to chromosomal problems at conception. It’s not your fault.

What is your chance of miscarriage at 7 weeks? 8 weeks? 12 weeks?

Here’s a table showing the risk of miscarriage by week (here’s the source):

WeekChance of miscarriage
3rd week30%
4th week25%
5th week19%
6th week11%
7th week7.2%
8th week5.8%
9th week3.3%
10th week3.2%
11th week1.9%
12th week1.7%
13th week1.3%
14th week1%

Here’s a chart showing the chance of miscarriage by week:

Remember that the weeks are counted from your last menstrual cycle. Typically, the egg gets fertilized at the beginning of Week 3, and the end of Week 4 is when you miss your period.

The 6th week is the second week after your missed period, and often the time of the first prenatal visit when you get an ultrasound. It has the highest risk of miscarriage, between 10-15%. After week 12, the risk is 1-2%.

It’s common to announce after the first trimester (roughly 12 weeks), but the risk of miscarriage decreases substantially by week 9. Soon, it’s well below 1%

Other factors that affect miscarriage:

  • Women with a previous miscarriage have a miscarriage chance of 25% in first trimester, compared to 4-5% for first pregnancies or women with a previous successful pregnancy. 
  • Age increases miscarriage rate: women below age 20 have a miscarriage rate of 4.4%; women aged 20-35 have a miscarriage rate of 6.7%; and women over 35 have a 19% miscarriage rate.
  • IVF pregnancies have miscarriage rates of 30%, vs 19% for natural pregnancies.
  • Vaginal bleeding signals increased risk – 13% of women with bleeding have miscarriages, vs 4.2% without.
  • Lack of nausea signals a higher miscarriage rate.
  • Low levels of progesterone may contribute to miscarriage.
Chance of Miscarriage by Week: Full Chart

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  • Why much parenting advice you hear is confusing or nonsense
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  • How much alcohol research shows you can drink safely while pregnant (it's more than zero)
  • The best foods to eat, and what foods you really should avoid

Allen Cheng

Allen Cheng is the founder of Shortform. He has a passion for non-fiction books (having read 200+ and counting) and is on a mission to make the world's best ideas more accessible to everyone. He reads broadly, covering a wide range of subjects including finance, management, health, and society. Allen graduated from Harvard University summa cum laude and attended medical training at the MD/PhD program at Harvard and MIT. Before Shortform, he co-founded PrepScholar, an online education company.

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