title: 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.
abstract: OBJECTIVE
  To compare the incidence of twin births and their birth weight characteristics in mothers aged > or = 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 > or = 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 > or = 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 > or = 5000 g, and frequencies of very low birth weight neonates.
  
  
  CONCLUSIONS
  Twin birth at the age of > or = 40 years is significantly more likely among either nulliparas or para > or = 4. Birth weight characteristics of twins delivered to mothers aged > or = 40 years are not different from those delivered to 35-39 years old mothers.
authors.affiliation: Department of Obstetrics and Gynecology, Kaplan Medical Center, Rehovot, Israel. blick@netvision.net.il
authors.forename: I
authors.initials: I
authors.lastname: Blickstein
authors.forename: R D
authors.initials: RD
authors.lastname: Goldman
authors.forename: R
authors.initials: R
authors.lastname: Mazkereth
mesh_terms: D000328:Adult; D001724:Birth Weight; D005260:Female; D006801:Humans; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D014427:Twins