93 Ann. N.Y. Acad. Sci. 1034: 93–100 (2004). © 2004 New York Academy of Sciences. doi: 10.1196/annals.1335.011 Number of Transferred Embryos How to Reduce Multiple Pregnancies MARC GERMOND, MARIE-PIERRE PRIMI, FRANÇOISE URNER, ALAIN CHANSON, DANIEL WIRTHNER, AND ALFRED SENN Reproductive Medicine Unit, Department of Gynecology and Obstetrics, CHUV, 1011 Lausanne, Switzerland ABSTRACT: Because the diagnostic tools for predicting whether an early cleav- age stage embryo can lead to a viable pregnancy are still elusive, transfer of more than one embryo remains quite common. However, the only way to reduce multiple pregnancies, considered as the main adverse effect of assisted reproductive technology, is to transfer a single embryo. In countries such as Switzerland and Germany, the law allows cryopreservation only at the 2-pro- nuclear stage. This restricts considerably the possibility of selecting the embry- os to be transferred. Therefore, a good cryopreservation program at the 2- pronuclear stage is an essential tool to optimize the efficiency of in vitro fertil- ization (IVF). We therefore recommend the Cumulated Singleton Delivery Rate (CUSIDERA) as a measure of standard IVF efficiency. This rate averages approximately 23.5% when calculated over the last 10 years in our unit and reaches a value above 35% for patients with more than 10 zygotes. Elective sin- gle-embryo transfers and the decrease of iatrogenic multiple pregnancies in IVF remain dependent on better prognostic tools for the appropriate selection of patients, gametes, and zygotes. KEYWORDS: multiple pregnancies; cumulated pregnancy rates; cumulated delivery rates; cryopreservation; pronuclear stage; treatment efficacy; IVF INTRODUCTION Success rates of in vitro fertilization (IVF) procedures depend, among other fac- tors, on the quantity and quality of the transferred embryos. Thus, occurrence of multiple gestations due to the transfer of more than one embryo has been considered by most professionals in the field as an inevitable, yet acceptable, hazard of the assisted reproductive technology (ART) treatments. However, the risks associated with multiple pregnancies on both mothers and children are not negligible. Indeed, preterm delivery associated with low birth weight, perinatal mortality, maternal mor- tality and morbidity, higher incidence of cerebral palsy, and other health problems in the newborn are some of the possible consequences of twin or triplet pregnan- cies. 1–3 Other important aspects to be taken into account are the economic conse- Address for correspondence: Marc Germond, Unité de Médecine de la Reproduction, Maternité, CHUV, CH-1011 Lausanne, Switzerland. Voice: 0041-21-314-32-57; fax: 0041-21-314-32-74. marc.germond@chuv.hospvd.ch