Objective: We compared perinatal mortality, preterm birth (<37, <33 and <28 weeks), small for gestational age (SGA), Apgar score (<4), mechanical ventilation (1 days) and prolonged neonatal intensive care unit (NICU) hospitalization (13 days) between twins of 25 to 34 and >35-year-old women. Further, we examined whether older maternal age effects were modified by parity or otherwise affected by chorionicity.
Study design: We carried out a population-based retrospective cohort study including all twin births in British Columbia (BC), Canada, from 1999 to 2003. The BC perinatal database registry was used to obtain clinical, behavioral and demographic data. Adjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated using generalized estimating equation models.
Result: Overall, twins of older women were more likely to be born preterm (<37 weeks), but not very or extremely preterm (<33 weeks). These twins were not at increased risk of perinatal death, mechanical ventilation or were not SGA compared with twins of younger women. Twins of older primiparous women did not have an elevated risk of NICU hospitalization; twins born to older multiparous women had higher risk (OR=1.8; 95% CI: 1.2 to 2.6). Analyses restricted to opposite-sex (dichorionic) twins showed that perinatal death, mechanical ventilation and very preterm birth occur less likely among older women (OR=0.2 (95% CI: 0.0 to 0.8), OR=0.3 (95% CI: 0.1 to 0.7) and OR=0.4 (95% CI: 0.2 to 0.7), respectively). Further, the risk of late preterm birth was increased and NICU hospitalization was reduced among opposite-sex twins born to older compared with younger primiparous women (OR=1.9 (95% CI: 1.3 to 2.8) and OR=0.2 (95% CI: 0.1 to 0.5), respectively).
Conclusion: Twins of older mothers did not have an elevated risk for most adverse birth outcomes, except for late preterm birth. Risks of neonatal care admission may be elevated among older multiparous women.