title: Effects of fetal number and multifetal reduction on length of in vitro fertilization pregnancies.
abstract: OBJECTIVE
  To determine the effects of multifetal reduction and other variables on the duration of gestation of in vitro fertilization (IVF) pregnancies.
  
  
  METHODS
  All 274 IVF pregnancies from the inception of the Women and Infants' Hospital IVF Program on May 26, 1988, until December 31, 1993, were evaluated.
  
  
  RESULTS
  Spontaneous reduction occurred in ten pregnancies, and multifetal reduction was elected in 28 multiple gestations. Among 260 pregnancies that remained viable beyond 20 weeks, 162 singletons (37.9 +/- 0.29 weeks; mean +/- standard error) had a longer mean gestation than did 64 twins (34.6 +/- 0.61 weeks), 25 pregnancies reduced to twins (33.4 +/- 1.0 weeks), or nine triplets (29.7 +/- 1.9 weeks). Triplets delivered 4.9 weeks earlier than nonreduced twins (P < .05) and 3.7 weeks before twins resulting from multifetal pregnancy reduction (P < .05). Regression analysis showed that at the 8-week ultrasound, each viable fetus could be expected to reduce the duration of the gestation by about 3.6 weeks, and each fetus reduced medically or as a result of natural causes could be expected to prolong the gestation by approximately 3.0 weeks. Only 14% of triplet pregnancies underwent spontaneous multifetal reduction.
  
  
  CONCLUSIONS
  Multifetal reduction of pregnancies with three or more fetuses was beneficial and increased the duration of gestation.
authors.affiliation: Department of Obstetrics and Gynecology, Brown University School of Medicine, Women and Infants' Hospital, Providence, Rhode Island, USA.
authors.forename: R V
authors.initials: RV
authors.lastname: Haning
authors.forename: D B
authors.initials: DB
authors.lastname: Seifer
authors.forename: C A
authors.initials: CA
authors.lastname: Wheeler
authors.forename: G N
authors.initials: GN
authors.lastname: Frishman
authors.forename: H
authors.initials: H
authors.lastname: Silver
authors.forename: D J
authors.initials: DJ
authors.lastname: Pierce
mesh_terms: D005260:Female; D005307:Fertilization in Vitro; D005313:Fetal Death; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D018607:Pregnancy Reduction, Multifetal; D011272:Pregnancy, Multiple; D012044:Regression Analysis; D013997:Time Factors