Objective To compare live birth rates blastocyst to live birth efficiency gestational age and birth weight in a large cohort of patients undergoing single versus double thawed blastocyst transfer. Single or double FBT. Main outcome measure(s) Live birth blastocyst to live birth efficiency pre-term birth low birth weight Results 1696 FBTs were analyzed. No differences were observed in patient age rate of embryo progression or post-thaw blastomere survival. Double FBT yielded a higher live birth per transfer; however 33 of births from double FBTs were twins versus only 0.6% of single FBTs. Double FBT was associated with significant increases in preterm birth and low birth weight the latter of which was significant even when the analysis was limited to singletons. 38% of blastocysts transferred via single FBT resulted in a live given birth to child versus only 34% with double FBT. This suggests that two single FBTs would result in more live given birth to children with significantly fewer preterm births when compared to double FBT. Conclusions Single FBT greatly decreased multiple and preterm birth risk while providing excellent live birth rates. Patients should be counseled that a greater overall number of live given birth to children per couple can be expected when thawed blastocysts are transferred one at a time. Support Intramural Research Program and the Program in Reproductive and Adult Endocrinology NICHD NIH. embryo transfer (6 11 12 13 14 However there is a paucity of data comparing single versus double frozen-thawed blastocyst transfer and study endpoints have been limited to pregnancy outcomes (clinical pregnancy live birth multiple birth miscarriage and ectopic) (15 16 Recently there has been a call for more substantial reporting of neonatal outcomes as opposed to ART cycle outcome alone (17 18 Our aim was to compare live birth rates blastocyst-to-live birth efficiency clinical pregnancy and multiple pregnancy rates as well as preterm birth and birth weight in a large cohort of patients undergoing single versus double vitrified-thawed blastocyst transfer. Materials CDC25A and methods Study Design We performed a retrospective cohort study of all autologous single and double vitrified-thawed blastocyst transfers with known live-birth outcomes performed at our center from January 2009 through April 2012. The study was performed at the Shady Grove Fertility and Reproductive Science Center in Rockville Maryland. Schulman Associates Institutional Review Board approved the retrospective review and analysis of data collected during routine clinical care. Patients All transfers of one or two autologous vitrified-warmed blastocysts from January 2009 through April 2012 were analyzed. Transfers of more than two embryos were excluded. Vitrification/Warming Etifoxine Modified Gardner and Schoolcraft grading was used to assess developing blastocysts (19). One of two senior embryologists reviewed all embryo grading Etifoxine as is usually routine clinical practice at our center. Supernumerary blastocysts with an inner cell mass/trophectoderm grade of greater than or equal to BB by day 5 or 6 post oocyte retrieval underwent vitrification. Over the duration of the study all embryo cryopreservation-thawing at our Etifoxine center was performed via a vitrification-warming method performed as previously described (20). Endometrial preparation protocol Patients underwent ovarian and uterine suppression using combined hormonal oral contraceptive pills. After baseline hormonal assessment and transvaginal ultrasound documenting no ovarian cysts and a thin endometrium patients were started on intramuscular estradiol valerate 4 mg every third day. When serum estradiol reached a level greater than 200 pg/mL and the endometrial double thickness was greater than or equal to 8mm on transvaginal ultrasound patients were started on 50mg daily intramuscular progesterone in oil. Embryo selection Number of blastocysts transferred was determined by patients and their physicians as per routine clinical practice. Decisions regarding the number of cryopreserved blastocysts to transfer at our center are generally made based on a number of factors including but not limited to Etifoxine age of the patient at the time of cryopreservation prior birth history; previous unsuccessful embryos transfers; the outcome of fresh embryo transfer Etifoxine cycles from which cryopreserved embryos were derived; the number of cryopreserved embryos available; medical and uterine factors; and infertility diagnosis. Though these are the primary factors generally.