title: Changes in fetal presentation in twin pregnancies.
abstract: OBJECTIVE
  The aim of the study was to describe the occurrence of spontaneous version in twins in the third trimester, as well as the correlation between antepartum and birth presentation.
  
  
  METHODS
  Twin pregnancies were divided into four gestational age intervals: 20-23; 24-27; 28-31; and 32-36 weeks. Fetal presentation was categorized as cephalic (C) or non-cephalic (NC). Hospital records were reviewed to determine demographic factors, including mode of conception. Chi-square was used to compare distributions of presentations, and Cramer's V measure of association was used to correlate presentations in individual pregnancies between antepartum intervals and birth.
  
  
  RESULTS
  A total of 207 pregnancies were included. The distribution of fetal presentations changed significantly through gestational age intervals (p < 0.001), although they were similar between 32-36 weeks and birth (p = 0.75). Correlation between antepartum and birth presentation in individual pregnancies strengthened throughout the four intervals. No correlation was seen between parity, gender, birthweight, or in vitro fertilization and fetal presentation or rate of spontaneous version.
  
  
  CONCLUSIONS
  Many twins undergo spontaneous version in the third trimester, though there is excellent correlation between presentation at 32-36 weeks and birth. A cephalic presenting twin at > or = 28 weeks is highly likely to be in cephalic presentation at delivery.
authors.affiliation: Weill Medical College of Cornell University, Department of Obstetrics and Gynecology, New York, NY 10021, USA. stchasen@med.cornell.edu
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Chasen
authors.forename: Stacey J
authors.initials: SJ
authors.lastname: Spiro
authors.forename: Robin B
authors.initials: RB
authors.lastname: Kalish
authors.forename: Frank A
authors.initials: FA
authors.lastname: Chervenak
mesh_terms: D016009:Chi-Square Distribution; D005260:Female; D005865:Gestational Age; D006801:Humans; D007746:Labor Presentation; D036801:Parturition; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D011272:Pregnancy, Multiple; D014427:Twins; D016216:Ultrasonography, Prenatal