['To compare quantitative pregnancy risk of nulliparous women 35 years and older with nulliparous women 25 to 29 years old.', 'Maternal records for first births at three suburban hospitals from July 1, 1986, to June 30, 1990, were studied, risk-assessed retrospectively according to a group-specific risk-scoring system, and compared statistically according to age and quantitative pregnancy risk.', 'The older women were more likely to be high risk (score > or = 10) prepregnancy (odds ratio [OR] 2.9, 95% confidence interval [CI] 1.9 to 4.5), antepartum (OR 1.6, 95% CI 1.3 to 2.0), intrapartum (OR 2.2, 95% CI 1.8 to 2.6), and cumulatively (OR 2.6, 95% CI 2.2 to 3.2) when compared with younger women. They were also more likely to be very high risk (score > or = 20) antepartum (OR 1.8, 95% CI 1.1 to 2.9), intrapartum (OR 2.1, 95% CI 1.5 to 2.8), and cumulatively (OR 2.5, 95% CI 2.0 to 3.2). Risk increased progressively through pregnancy, revealing the intrapartum period as the time interval of maximum risk. Based on cumulative risk scoring, 64.9% of the older women were at least high risk, compared with 41.3% of the younger women (OR 2.6, 95% CI 2.2 to 3.2).'] Is age greater than thirty-four years an independent pregnancy risk factor in nulliparous women?