title: Factors determining early pregnancy loss in singleton and multiple implantations.
abstract: BACKGROUND
  The incidence of first trimester pregnancy loss is much lower in IVF twin pregnancies than in IVF singleton pregnancies. The objective of this study was to determine which embryonic and maternal factors contribute to this finding.
  
  
  METHODS
  Retrospective data analysis of the outcome of 1593 pregnancies after day 3 double-embryo transfer (DET) after IVF or ICSI treatment.
  
  
  RESULTS
  Of 1148 single implantations at 6 weeks, 936 (81.5%) were ongoing pregnancies. Of 445 multiple implantations at 6 weeks, 354 (79.6%) were ongoing multiple pregnancies, 80 (17.9%) were ongoing singleton pregnancies and 11 (2.5%) ended in a spontaneous abortion. Total pregnancy loss was 18.5 and 2.5% (P < 0.001) in singleton and twin gestations, respectively. Loss per gestational sac was 18.5 and 11.46% (P < 0.001), respectively. Determinants contributing to the continuation of gestation beyond 6 weeks were young maternal age, possibility to cryopreserve embryos and short GnRH agonist flare-up stimulation protocol. Whereas factors promoting multiple implantation at 6 weeks of gestation were young maternal age, high cumulative embryo score (CES), male infertility, long stimulation protocol and thick endometrium.
  
  
  CONCLUSIONS
  Although multiple implantation at 6 weeks is predominantly determined by (morphological) embryo quality, the continuation of pregnancy beyond 6 weeks becomes more dependent on the combination of genetic and developmental potential of the embryo(s) and an optimal uterine milieu.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Medicine, Vrije University Medical Center, Amsterdam, The Netherlands. mj.lambers@vumc.nl
authors.forename: M J
authors.initials: MJ
authors.lastname: Lambers
authors.forename: E
authors.initials: E
authors.lastname: Mager
authors.forename: J
authors.initials: J
authors.lastname: Goutbeek
authors.forename: J
authors.initials: J
authors.lastname: McDonnell
authors.forename: R
authors.initials: R
authors.lastname: Homburg
authors.forename: R
authors.initials: R
authors.lastname: Schats
authors.forename: P G A
authors.initials: PG
authors.lastname: Hompes
authors.forename: C B
authors.initials: CB
authors.lastname: Lambalk
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology / Q000209:etiology*; D000328:Adult; D015925:Cryopreservation; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008423:Maternal Age; D009426:Netherlands / Q000453:epidemiology; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First; D011272:Pregnancy, Multiple; D012044:Regression Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D020554:Sperm Injections, Intracytoplasmic; D014427:Twins