Share of U.S. Births to Mothers Aged 30 to 34

## What this measures

The share of all babies born in the United States in a year whose mothers were aged 30 to 34: births in the group divided by all births, in percent. Annual, from 1995.

## Why it matters

It shows how the age of motherhood is moving, independent of whether the total number of births is rising or falling. Read across the six groups, it is the clearest picture of the shift toward having children later.

## How to read it

Percent of all births in the year. The six groups add up to 100 (to rounding). The share of one group can rise because births in that group grew or because births in the others fell; compare with the count (demography.cdc.births.mother_age.30_34).

## What it does not say

Births are counted where they occur in the United States, to residents and non-residents alike, by the year of birth. Final data only: the newest year appears about nine months after it ends. A mother's age is as recorded on the birth certificate; where it is missing NCHS imputes it. Counts say nothing about why births moved: the number of women in each age group changes with past births and migration, so a falling count can reflect fewer women of that age as much as different choices. The share is Palanor's arithmetic on the NCHS counts (births in the group ÷ all births × 100, two decimals); NCHS publishes the counts.

## Source

CDC WONDER Natality databases (wonder.cdc.gov): 1995-2002, 2003-2006 and 2007 to the latest final year, from the National Vital Statistics System birth certificates compiled by the National Center for Health Statistics (NCHS). Read through the WONDER API, national figures only. Public domain; use does not imply CDC endorsement. WONDER's data-use restrictions apply: health statistical reporting and analysis only, and no count of 9 or fewer is published. Palanor checks monthly; NCHS adds a final year once a year.