Factors determining early pregnancy loss in singleton and multiple implantations.

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.