title: A comparison of pregnancy outcomes between day 3 and day 5/6 embryo transfers: does day of embryo transfer really make a difference?
abstract: OBJECTIVE
  To determine if day of embryo transfer (ET) affects gestational age (GA) and/or birth weight (BW) at a single university fertility center that primarily performs day 5/6 ET.
  
  
  METHODS
  Retrospective cohort study of 2392 singleton live births resulting from IVF/ICSI at a single large university fertility center from 2003 to 2012. Patients were stratified by day 3 or day 5/6 ET. Outcome variables included patient age, gravidity, prior miscarriages, prior assisted reproduction technology cycles, number of embryos transferred, number of single ET, infertility diagnosis, neonatal sex, GA at birth, and BW. Subanalyses were performed on subgroups of preterm infants. A comparison was made between the study data and the Society of Assisted Reproductive Technologies (SART) published data.
  
  
  RESULTS
  There was no difference in GA at birth (39 ± 2.1 weeks for day 3 ET, 39 ± 1.9 weeks for day 5/6 ET) or BW between ET groups (3308 ± 568 g for day 3 ET, 3268 ± 543 g for day 5/6 ET). There was also no difference in the number of preterm deliveries (8.5 % for day 3 ET vs. 10.8 % for day 5/6 ET). The day 5/6 ET study data had significantly fewer pre-term deliveries than the SART day 5/6 ET data.
  
  
  CONCLUSIONS
  In contrast to published SART data, GA and BW were not influenced by day of ET. Data may be more uniform at a single institution. Day 5/6 ET continues to offer improved pregnancy rates without compromising birth outcomes.
authors.affiliation: New York University Fertility Center, New York University Langone Medical Center, 660 First Ave, 5th Floor, New York, NY, 10016, USA, susan.mcclelland@nyumc.org.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Maxwell
authors.forename: Katherine
authors.initials: K
authors.lastname: Melzer-Ross
authors.forename: David H
authors.initials: DH
authors.lastname: McCulloh
authors.forename: James A
authors.initials: JA
authors.lastname: Grifo
mesh_terms: D000328:Adult; D015331:Cohort Studies; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D050498:Live Birth; D008297:Male; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D047928:Premature Birth; D012189:Retrospective Studies; D056826:Single Embryo Transfer