The background risks, and how few of them have been measured recently
A table doctors have used for decades. Three of its twelve rows can be brought up to date from American data.
There is a table that has circulated in obstetrics for decades, setting out the risks every pregnancy carries before anything unusual happens. It was published in an ethics paper arguing that expecting a perfect baby causes real harm, which is the same argument this part of the guide makes.
It is a good table and it deserves an honest look. Most of it has not been remeasured in a long time.
| Risk | The old figure | Where it stands now |
|---|---|---|
| Preterm birth, before 37 weeks | 69,000 per million | 104,100 per million, which is 10.41% of US births in 2024. The largest change in the table. |
| Stillbirth at 20 weeks or later | 4,000 to 20,900 per million | 5,530 per million in 2023, counted per million live births plus stillbirths, which is not the same denominator the old row used. |
| Birth defects, all causes | 30,000 per million | Unchanged. This is the 1 in 33 figure, and it is the one row that has held up. |
| Miscarriage after the pregnancy is recognised | 150,000 per million | About 128,000 per million, from Norway. No equally good American figure exists. |
| Very early loss, before a pregnancy is recognised | 350,000 per million conceptions | The measurement that exists is per million pregnancies already implanted, not per conception. Nobody has counted conceptions. |
| Genetic disease of all kinds | 110,000 per million | The best count anyone has is from British Columbia in 1988, and it is roughly half that. |
| Chromosome conditions | 5,000 per million | No current American figure exists for all of them. National surveillance follows only trisomy 21, 18 and 13. |
| Growth restriction | 30,000 per million | Depends entirely on where you draw the line. A below tenth centile definition makes it about 10% by arithmetic. |
Three of the twelve rows can be brought up to date from current US vital statistics, and one was already right. The rest rest on Canadian or Norwegian data, on work now thirty-five to forty years old, or on denominators that were never measurable in the first place.
What that tells you, and what it does notIt does not mean the old figures are lies, or that pregnancy is riskier than the table says. Most of these risks are genuinely small and genuinely stable. What it means is that a table which looks like settled arithmetic is partly a record of what nobody has counted lately. Growth restriction has no fixed rate because it has no fixed definition. Nobody knows how many conceptions are lost, because a conception nobody detects cannot be counted.
When a number is quoted to you as though it were measured, it is fair to ask when, where, and out of what.
When a number is quoted to you as though it were measured, it is fair to ask when, where, and out of what.
Worth asking about any figure you are given"How old is that number?"
"Was it measured in the United States?"
"Is that out of all pregnancies, or only the ones that reached a live birth?"
"Was it measured in the United States?"
"Is that out of all pregnancies, or only the ones that reached a live birth?"
Where this comes from:
800. Chervenak FA, McCullough LB, Brent RL. The perils of the imperfect expectation of the perfect baby. Am J Obstet Gynecol. 2010;203(2):101.e1-101.e5.
801. Baird PA, Anderson TW, Newcombe HB, Lowry RB. Genetic disorders in children and young adults: a population study. Am J Hum Genet. 1988;42(5):677-693.
802. Wilcox AJ, Weinberg CR, O'Connor JF, Baird DD, Schlatterer JP, Canfield RE, et al. Incidence of early loss of pregnancy. N Engl J Med. 1988;319(4):189-194.
803. Magnus MC, Wilcox AJ, Morken NH, Weinberg CR, Haberg SE. Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study. BMJ. 2019;364:l869.
804. Osterman MJK, Hamilton BE, Martin JA, Driscoll AK, Valenzuela CP. Births: final data for 2024. Natl Vital Stat Rep. 2026;75(2).
805. Gregory ECW, Valenzuela CP, Hoyert DL. Fetal mortality: United States, 2023. Natl Vital Stat Rep. 2025;74(8).
509. Society for Maternal-Fetal Medicine (SMFM); Martins JG, Biggio JR, Abuhamad A. Society for Maternal-Fetal Medicine Consult Series #52: diagnosis and management of fetal growth restriction. Am J Obstet Gynecol. 2020;223(4):B2-B17.
796. Centers for Disease Control and Prevention; National Birth Defects Prevention Network. Prevalence of selected birth defects from population-based birth defects surveillance programs in the United States, 2018-2022 [data brief]. Atlanta (GA): CDC; April 2026.
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This page is educational. It supports the conversation with your own clinicians. It is not consent to any treatment, and it cannot assess you. If you are worried about a symptom now, see urgent warning signs.