OBJECTIVE: To examine the extent to which the odds of birth, pregnancy, or adverse birth outcomes are higher among women aged 28 to 36 years who use fertility treatment compared with untreated women. DESIGN: Prospective, population-based. SETTING: Not applicable. PATIENT(S): Participants in the ALSWH born in 1973 to 1978 who reported on their infertility and use of in vitro fertilization (IVF) or ovulation induction (OI). INTERVENTION(S): Postal survey questionnaires administered as part of ALSWH. MAIN OUTCOME MEASURE(S): Among women treated with IVF or OI and untreated women, the odds of birth outcomes estimated by use of adjusted logistic regression modeling. RESULT(S): Among 7,280 women, 18.6% (n = 1,376) reported infertility. Half (53.0%) of the treated women gave birth compared with 43.8% of untreated women. Women with prior parity were less likely to use IVF compared with nulliparous women. Women using IVF or OI, respectively, were more likely to have given birth after treatment or be pregnant compared with untreated women. Women using IVF or OI were as likely to have ectopic pregnancies, stillbirths, or premature or low birthweight babies as untreated women. CONCLUSION(S): More than 40% of women aged 28-36 years reporting a history of infertility can achieve births without using treatment, indicating they are subfertile rather than infertile.