Single embryo transfer reduces the risk of perinatal mortality, a population study

STUDY QUESTION: Do births following single embryo transfers (SET) have a reduced risk of perinatal mortality compared with those following double embryo transfers (DET)? SUMMARY ANSWER: SET is associated with reduced risk of perinatal mortality compared with DET. WHAT IS KNOWN ALREADY: Fetal, neonatal and perinatal mortality are important indicators for monitoring pregnancy and childbirth, particularly for births following assisted reproductive technology (ART) treatments. Following the introduction of SET, there has been a decline in the perinatal mortality rate (PMR) among babies born after ART in Australia and New Zealand. STUDY DESIGN, SIZE, DURATION: This population study (census) included 50,258 births of ≥ 20 weeks gestation and/or ≥ 400 g of birthweight following embryos transfer cycles in Australia and New Zealand during the period 2004-2008. PARTICIPANTS/MATERIALS, SETTING, METHODS: The PMR was calculated according to the number of embryos transferred and other demographic and treatment-related factors. Perinatal deaths were defined as the number of fetal deaths (stillbirths) plus the number of neonatal deaths (deaths that occur before 28 days after birth). MAIN RESULTS AND THE ROLE OF CHANCE: The PMR was 16.2 per 1000 births (n= 813). Of the 813 perinatal deaths, 630 were fetal deaths and 183 neonatal deaths. Twins had a significantly higher PMR (27.8 per 1000 births) than singletons (12.4 per 1000 births). The risk of perinatal mortality for all births following DET was 53% higher than for all births following SET (adjusted risk ratio 1.53, 95% confidence interval (95% CI): 1.29-1.80). Births following fresh DET had a 58% increased risk of perinatal mortality compared with births following fresh SET (risk ratio 1.58, 95% CI: 1.32-1.90). LIMITATIONS, REASONS FOR CAUTION: Information on outcomes was missing from <1% of clinical pregnancies recorded in Australian and New Zealand Assisted Reproduction Database for the study period. There are no data on the timing of fetal death, the cause of perinatal death or on late termination of pregnancy at ≥ 20 weeks' gestation. WIDER IMPLICATIONS OF THE FINDINGS: Double and higher order embryo transfer is associated with a higher risk of perinatal mortality when compared with SET. The number of embryos transferred is determined by the clinician with consent of the patient and is a modifiable treatment factor. SET should be advocated as the first-line management in ART as it is the single most effective public health intervention for preventing excess perinatal mortality among ART pregnancies. STUDY FUNDING/COMPETING INTEREST(S): Nil.