Reference summary — not medical advice or a personal risk estimate.
Late age at first full-term pregnancy
Quick answer
Not IARC-classified — this is not a chemical or physical agent IARC rates. Recognized as a cancer risk factor based on observational evidence. Reproductive history. Applies to people who have their first full-term pregnancy after age 30.
Summary
Women who have their first full-term pregnancy after age 30 have roughly double the breast cancer risk of women who have their first full-term pregnancy before age 20.
What's not established
This is a population-level association from observational studies, not a cause-and-effect finding. It does not establish your personal risk, does not mean delaying pregnancy is inadvisable for other reasons, and does not quantify how this factor combines with your other individual risk factors.
Evidence sources
Every claim on this page traces back to one of these. Click through to read the primary document yourself.
Primary sources
NCI
NCI — Reproductive History and Cancer Risk
Last reviewed: October 2026
Official reference list
A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.
- California Prop 65 list
State of California's list of chemicals known to cause cancer or reproductive harm.