title: Cohort study of twinning in an academic health center: changes in management and outcome over forty years.
abstract: OBJECTIVE
  Our purpose was to explore the management and outcomes of twin pregnancies over 40 years (1952 to 1993) within a single academic health center.
  
  
  METHODS
  According to a retrospective cohort design, twin pregnancies were collected and the following variables were analyzed: maternal age, parity, gestational age, birth weight, twin gender, presentation, delivery route, intervals between births, Apgar scores, and perinatal outcome. Information was broken into approximately decade-long epochs (1952 to 1962, 1963 to 1972, 1973 to 1982, 1983 to 1993) to compare trends over time.
  
  
  RESULTS
  A total of 814 twin pregnancies were delivered. Median birth weight and gestational age decreased over time. The prevalence of > 20% birth weight discordancy was 23% and did not increase. Nulliparity increased over time but maternal age did not. Same-sex pairs were constant, as was presentation. Use of abdominal delivery and the abdominal delivery of a nonvertex second twin after vaginal delivery of the first increased in the last two epochs. Both the interval between births and the Apgar score of the second twin increased over time. Perinatal mortality of very-low-birth-weight and normal-birth-weight twins decreased over time.
  
  
  CONCLUSIONS
  The maternal demographics of twinning changed little over 40 years. Gestational age and birth weight decreased over time because of the regionalization of perinatal care. Birth weight-specific perinatal mortality improved over time.
authors.affiliation: Department of Obstetrics and Gynecology, University of North Carolina, Chapel Hill 27599-7570, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Saacks
authors.forename: J M
authors.initials: JM
authors.lastname: Thorp
authors.forename: C H
authors.initials: CH
authors.lastname: Hendricks
mesh_terms: D000328:Adult; D001034:Apgar Score; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012744:Sex Ratio; D014427:Twins