Perinatal outcome in singletons after modified natural cycle IVF and standard IVF with ovarian stimulation.

Singletons born after IVF treatment are at risk for adverse pregnancy outcome, the cause of which is unknown. The aim of the present study was to investigate the influence of ovarian stimulation on perinatal outcome. In this single-centre retrospective study, perinatal outcome of singleton pregnancies resulting from IVF treatment with (n=106) and without ovarian stimulation (n=84) were compared. For IVF without ovarian stimulation, a modified natural cycle protocol was used. No differences were found in pregnancy duration, proportion of prematurity and proportion of low birth weight. Mean birth weight of modified natural cycle vs standard IVF singletons was 3485 (+/-527) vs 3218 (+/-670)g; P=0.003. After adjustment for prognostic factors by linear regression analysis, the difference in birth weight remaining was 134 g; P=0.045. Birth weights of modified natural cycle IVF singletons found in this study are higher than standard IVF singletons, suggesting that ovarian stimulation may be a causative factor in the occurrence of low birth weight in standard IVF.