Why do singletons conceived after assisted reproduction technology have adverse perinatal outcome? Systematic review and meta-analysis.
OBJECTIVE To compare the perinatal outcomes of babies conceived by single embryo transfer (SET) with those conceived by double embryo transfer (DET). DESIGN, SETTING AND PARTICIPANTS A retrospective population-based study of embryo transfer cycles in Australia and New Zealand between 2002 and 2006, using data from the Australia and New Zealand Assisted Reproduction Database. MAIN OUTCOME MEASURES Proportion of SET procedures; comparison of SET and DET procedures with respect to multiple births, low birthweight (LBW), preterm birth and fetal death. RESULTS The proportion of SET procedures has increased from 28.4% in 2002 to 32.0% in 2003, 40.5% in 2004, 48.2% in 2005 and 56.9% in 2006. The multiple birth rate for all babies conceived by SET (4.0%) was 10 times lower than for those conceived by DET (39.1%) (P < 0.01). The average birthweight for all liveborn babies conceived by SET (3290 g) was higher than for those conceived by DET (2934 g) (P < 0.01). The preterm birth rate of all DET-conceived babies (30.3%) was higher than for SET-conceived babies (12.3%) (adjusted odds ratio [AOR], 3.19 [95% CI, 3.01-3.38]). All babies conceived by DET were more likely to be stillborn than those conceived by SET (AOR, 1.49 [95% CI, 1.21-1.82]). Singletons conceived by DET were more likely to be born preterm than singletons conceived by SET (AOR, 1.13 [95% CI, 1.05-1.22]). Liveborn singletons conceived by DET were 15% more likely to have LBW than liveborn singletons conceived by SET (AOR, 1.15 [95% CI, 1.05-1.26]). There was no significant difference in fetal death rate between DET- and SET-conceived singletons. CONCLUSION The increase in proportion of SET procedures has resulted in a lower rate of multiple births and in better perinatal outcomes in Australian and New Zealand assisted reproduction programs.