title: Cesarean section for the second twin: a population-based study of occurrence and outcome.
abstract: BACKGROUND
  Although management of twin deliveries has been a topic of discussion for decades, a consensus on how to deliver twins is lacking. The objective of this study was to examine short-term neonatal outcome of the second twin delivered by cesarean section after vaginal delivery of the first-born twin (combined delivery) and to identify predictors of combined delivery.
  
  
  METHODS
  This study was a 3-year, population-based, retrospective cohort investigation of 1,254 twin births in Denmark. The twin births were divided into three groups: vaginal deliveries, planned cesarean deliveries, and combined deliveries. Data were extracted from medical records, a fetal medicine software program (Astraia), and the National Birth Registry. Short-term poor neonatal outcome was measured as a 5-minute Apgar score ≤ 7, umbilical cord pH ≤ 7.10, and admission to neonatal intensive care unit for more than 3 days.
  
  
  RESULTS
  Vertex-nonvertex fetal presentations were more prevalent in combined deliveries than vaginal deliveries (OR 4.4, 2.5-7.8). Nonvertex second twins born by combined delivery had a higher risk of Apgar score ≤ 7 and umbilical cord pH ≤ 7.10 compared with vaginal delivery, unadjusted OR 6.2 (2.1-18), and unadjusted OR 3.9 (1.6-9.5). Prenatal ultrasound scans were evaluated in combined deliveries, of which 48 percent were vertex-vertex at the last ultrasound scan in pregnancy (mean gestational age 34 + 0) and 37 percent were vertex-vertex at birth.
  
  
  CONCLUSIONS
  Vertex-nonvertex presenting twins have an increased risk of combined delivery. Combined deliveries are associated with increased neonatal morbidity for the second twin.
authors.affiliation: Department of Obstetrics and Gynecology,University Hospital Roskilde, Roskilde, Denmark.
authors.forename: Line
authors.initials: L
authors.lastname: Engelbrechtsen
authors.forename: Elise Hoffmann
authors.initials: EH
authors.lastname: Nielsen
authors.forename: Trine
authors.initials: T
authors.lastname: Perin
authors.forename: Anna
authors.initials: A
authors.lastname: Oldenburg
authors.forename: Ann
authors.initials: A
authors.lastname: Tabor
authors.forename: Lillian
authors.initials: L
authors.lastname: Skibsted
mesh_terms: D000328:Adult; D001034:Apgar Score; D002585:Cesarean Section; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D007746:Labor Presentation; D011247:Pregnancy; D059285:Pregnancy, Twin; D012042:Registries; D012189:Retrospective Studies; D014470:Umbilical Cord / Q000737:chemistry*
keywords: combined delivery; fetal presentation; neonatal outcome; twin delivery