title: Impact of advanced maternal age on neonatal survival of twin small-for-gestational-age subtypes.
abstract: OBJECTIVE
  We examined the impact of advanced maternal age (>40 years old) on the survival of twin small-for-gestational-age (SGA) infants, that is, infants who were smaller in size than was expected for the baby's sex, genetic heritage, and gestational age.
  
  
  METHODS
  The present study was a retrospective cohort study on twin live births in the USA from 1995 to 1998 inclusive. Two categories of SGA babies were defined: discordant (when only one of a twin pair was SGA) and concordant (when both were SGA). Otherwise, the twin pair was appropriate-for-gestational-age (AGA) concordant.
  
  
  RESULTS
  192,195 twin pairs were analyzed. The incidence of SGA discordance and concordance was 11.8% and 3.9%, respectively. The occurrence of both SGA subtypes tended to decrease with increasing maternal age. The unadjusted risk for neonatal mortality increased when both twins were affected (15.8: 22.8 and 56.6 per 1000 among AGA concordant, SGA discordant and SGA concordant twins; P-value for trend < 0.0001). Using maternal-age-specific AGA babies as reference, the adjusted risk for neonatal mortality climbed progressively with advancing maternal age in a dose-dependent pattern, being lowest among teenagers and highest in mothers aged > or =40 years.
  
  
  CONCLUSIONS
  SGA discordance and concordance declined with advancing maternal age. In contrast, neonatal mortality of both SGA subtypes worsened with the increase in maternal age compared with that of the age-specific AGA infants. These findings are potentially useful to care providers in counseling older women, a group that is progressively increasing in size and is most susceptible to twining.
authors.affiliation: Department of Epidemiology and International Health, University of Alabama at Birmingham, Alabama 35294-0022, USA. sibylle@uab.edu
authors.forename: Sibylle
authors.initials: S
authors.lastname: Kristensen
authors.forename: Hamisu M
authors.initials: HM
authors.lastname: Salihu
authors.forename: Louis G
authors.initials: LG
authors.lastname: Keith
authors.forename: Russell S
authors.initials: RS
authors.lastname: Kirby
authors.forename: Mary A B
authors.initials: MA
authors.lastname: Pass
authors.forename: Karen B
authors.initials: KB
authors.lastname: Fowler
mesh_terms: D005260:Female; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000502:physiology*; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D012189:Retrospective Studies; D014427:Twins / Q000502:physiology*