Delayed childbearing and risk of adverse perinatal outcome. A population-based study.

OBJECTIVE--To investigate the effect of advancing maternal age on pregnancy outcome among healthy nulliparous women, after adjustment for demographic characteristics, smoking, history of infertility, and other medical conditions. DESIGN--A population-based cohort study was conducted with prospectively collected data from the Swedish Medical Birth Register. PATIENTS--Nulliparous Nordic women (N = 173,715), aged 20 years and above, who delivered single births at Swedish hospitals from 1983 through 1987. OUTCOME MEASURES--Late fetal and early neonatal death rates; rates of very low birth weight (VLBW, less than 1500 g), moderately low birth weight (MLBW, 1500 through 2499 g), very preterm delivery (less than or equal to 32 weeks), moderately preterm delivery (33 through 36 weeks), and small-for-gestational-age (SGA) infants (less than -2 SDs). RESULTS--Compared with women aged 20 to 24 years, women aged 30 to 34 years had significantly higher adjusted odds ratios (ORs) of late fetal deaths (OR = 1.4); VLBW (OR = 1.2); MLBW (OR = 1.4); very preterm birth (OR = 1.2); and SGA infants (OR = 1.4). Among women aged 35 to 39 years, the adjusted OR was significantly higher for VLBW (OR = 1.9); MLBW (OR = 1.7); very preterm birth (OR = 1.7); moderately preterm birth (OR = 1.2); and SGA infants (OR = 1.7). Among women 40 years old and older, the adjusted OR was significantly higher for VLBW (OR = 1.8); MLBW (OR = 2.0); very preterm birth (OR = 1.9); moderately preterm birth (OR = 1.5); and SGA infants (OR = 1.4). CONCLUSIONS--Delayed childbearing is associated with an increased risk of poor pregnancy outcomes after adjustment for maternal complications and other risk factors.