Incidence and birth weight characteristics of twins born to mothers aged 40 years or more compared with 35-39 years old mothers: A population study

Objective: To compare the incidence of twin births and their birth weight characteristics in mothers aged ≥ 40 years with those of mothers aged 35-39 years. Methods: We used a population-based cohort of Israeli twins delivered between 1993-98 to compare birth weight characteristics of 510 and 2102 twin pairs delivered to mothers aged ≥ 40 years (cases) and 35-39 years (controls), respectively. Results: The incidence of twin mothers aged 40 years or more increased 50% during the study period, ten times more than mothers aged 35-39. There were significantly more nulliparas (P < .001, OR 1.54, 95% CI 1.2, 1.9) and more para ≥ 4 (P < .004, OR 1.38, 95% CI 1.1, 1.7) among older mothers. Irrespective of parity, there were no significant differences between mean twin birth weight, total twin birth weight < 3000 g, 3000-4999 g, and ≥ 5000 g, and frequencies of very low birth weight neonates. Conclusions: Twin birth at the age of ≥ 40 years is significantly more likely among either nulliparas or para ≥ 4. Birth weight characteristics of twins delivered to mothers aged ≥ 40 years are not different from those delivered to 35-39 years old mothers.