Embryonic synergism may reduce pregnancy loss: a multivariate regression analysis

Objective To evaluate clinical and assisted reproductive technology (ART) cycle variables related to spontaneous embryo reduction. Design Observational retrospective cohort study. Setting Private ART center. Patient(s) A total of 3,467 patients achieving a first-trimester pregnancy after IVF. Intervention(s) None. Main Outcome Measure(s) Rate of any spontaneous embryo reduction and rate of spontaneous single embryo reduction. Result(s) Adjusting for all analyzed variables, only initial gestational sac count, age, and body mass index were associated with the spontaneous embryo reduction rate. Twins had a lower chance of having a spontaneous embryo reduction than singletons (odds ratio 0.6, 95% confidence interval 0.50–0.79). When only spontaneous single embryo reduction was assessed, women with two or three initial gestational sacs were less prone to have a spontaneous single embryo reduction than women with one initial gestational sac. Conclusion(s) When spontaneous embryo reduction and spontaneous single embryo reduction were evaluated independently of other clinical and ART cycle variables, they were less frequent in twin pregnancies than in singleton pregnancies. This suggests a role for embryonic synergism in sustaining implantation.