Factors affecting obstetric outcome of singletons born after IVF.

BACKGROUND: Singletons born after IVF have an adverse perinatal outcome when compared with singletons in the general population. This study investigates maternal characteristics and IVF- treatment-related variables, for a possible influence on obstetric outcomes.

METHODS: Data from all IVF clinics in Sweden, including all IVF singletons born after fresh treatment cycles and own oocytes during 2002-2006, were included (n = 8941) and cross-linked with the Swedish Medical Birth Registry. Four major outcomes were investigated: very preterm birth (<32 weeks), small for gestational age (SGA), placenta previa and placental abruption. Maternal characteristics (age, parity, BMI, smoking and years of infertility) and treatment-related variables (number of oocytes retrieved, number of embryo culture days, number of transferred and cryopreserved embryos, 'vanishing twin') were investigated for independent association with the four selected outcomes. Adjusted odds ratios (AORs) were calculated by logistic regression.

RESULTS: Primiparity, smoking, BMI and 'vanishing twin' were associated with an increased risk of very preterm birth. Maternal age, primiparity, smoking, BMI and years of infertility were associated with an increased risk of SGA. Maternal age and blastocyst transfer were associated with an increased risk, and primiparity with a decreased risk, of placenta previa. Smoking was significantly associated with placental abruption.

CONCLUSIONS: In singletons born after fresh IVF, certain maternal characteristics and the number of embryos transferred, when there was a 'vanishing twin' affected the obstetric outcome negatively. An increased rate of placenta previa was observed after blastocyst transfer. The results support the use of single embryo transfer and indicate that lifestyle factors are important for obstetric outcome.