Premature Birth: Chances of Baby Survival

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 premature birth occurs before 36 weeks and occurs in 12% of pregnancies. Early-term is between 37-38 weeks, and full-term is 39 and beyond.

Over the past decades, survival for preterm babies has increased dramatically due to improvements like assisted ventilation (lungs develop later in pregnancy). It’s a marvel that even babies born at 22 weeks still have a shot at survival.

What are the specific chances of survival for each week of pregnancy? How likely is a baby to survive at 24 weeks, vs 26 weeks, and 28 weeks?

Despite their chance of survival, premature children are more likely to get sick, have lower IQs, and may have vision/hearing problems. 75% of 5-year-olds born before 30 weeks have a disability (vs 27% of full-term births). Their IQs were 5-14 points lower.

Here’s a table of % of births occurring at each week of gestation:

Weeks of Gestation% of BirthsProbability of Death in First Year

Chances of a preterm baby are thus sizable, but still in the small minority.

The overall story is, premature babies can be born at a <10% chance, and they have a good rate of survival.

Premature Birth: Chances of Baby Survival

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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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