Down syndrome chance by age

The figures are maternal-age-specific live-birth estimates for Down syndrome (trisomy 21) — the chance measured at delivery, not earlier in pregnancy when it is higher. They follow the widely used estimates from Morris, Mutton and Alberman (2002) and the earlier Hook data, and land at familiar anchors: roughly 1 in 1,480 at age 20, about 1 in 940 at 30, 1 in 353 at 35, 1 in 85 at 40, and around 1 in 35 at 45. Different sources publish slightly different numbers, so treat these as estimates of a population trend rather than exact values.

No. Age shifts the odds across a whole population, but it cannot tell you anything specific about your pregnancy. Even at age 45, where the chance is highest on this table, roughly 34 in every 35 babies do not have Down syndrome. And Down syndrome happens at every age — most of the chance comes down to how chromosomes happen to divide, which is largely down to luck, not something you did or can control. Think of your age as a starting point, a prior, that a screening test then refines far more precisely.

The age number is just a baseline from statistics; a screening test looks at your actual pregnancy and updates it. First-trimester combined screening and cell-free DNA screening (NIPT) both give a far more personalized chance than age alone. But screening is not diagnosis. A key idea is the positive predictive value: what a 'positive' or 'high-chance' result actually means depends on how likely Down syndrome was to begin with. The same positive NIPT result is more likely to be a false alarm in a younger person (lower starting chance) than in an older one (higher starting chance). That's why any positive screen is confirmed with diagnostic testing — CVS or amniocentesis — before anything is certain.

Because far more babies overall are born to younger mothers. The per-pregnancy chance is lower at, say, 25 than at 40 — but there are so many more pregnancies in the younger group that the larger share of babies with Down syndrome are still born to women under 35 (historically about 8 in 10). It's a good reminder that age is a weak predictor for any individual: a low number spread across a huge number of pregnancies still adds up. This is exactly why screening is offered to people of every age, not only those over 35.

No. Prenatal screening for chromosomal conditions is offered to everyone but is entirely optional and personal. Some people want as much information as early as possible; others prefer not to test, because the result would not change how they feel about their pregnancy, or because they would rather avoid the follow-up decisions. There is no wrong choice, and choosing not to screen is just as valid as choosing to. A genetic counselor or your prenatal provider can walk through what each test can and cannot tell you, so the decision fits your own values and situation.

Yes. This tool runs entirely in your browser. The age you pick is used on your own device to look up a published estimate and is never sent to a server, saved, or shared — close the tab and it's gone. In a post-Dobbs world we treat reproductive data as sensitive by default. It's general educational information based on published prevalence estimates and screening guidance; it is not medical advice, a diagnosis, or a prediction about your pregnancy.