Multifetal pregnancy reduction is not associated with an increased risk of intrauterine growth restriction, except for very-high-order multiples

OBJECTIVE: Our purpose was to investigate whether multifetal pregnancies reduced to twins have an increased risk of intrauterine growth restriction and discordant birth weight. STUDY DESIGN: This retrospective cohort study investigated the rates of birth weight discordance >20% and intrauterine growth restriction using both twin and singleton birth weight curves in 441 twin deliveries after multifetal pregnancy reduction (233 reduced from triplets, 156 from quadruplets, and 52 from quintuplets or greater) compared with 136 nonreduced dichorionic twins. RESULTS: No significant difference was found in the frequency of birth weight discordance and in the overall incidence of intrauterine growth restriction by both twin and singleton birth weight curves when pregnancies that underwent multifetal pregnancy reduction were compared with the control group. There was, however, an almost twofold increase in the rate of intrauterine growth restriction in pregnancies with a starting fetal number of 5 or more (23.1%) compared with that in those reduced from triplets or quadruplets (12.1%) when the twin curve standard was used (P = .03). This difference disappeared when these groups were compared with a singleton nomogram. CONCLUSION: This study suggests that multifetal pregnancy reduction is not associated with an increased risk of intrauterine growth restriction unless the starting fetal number is ≤5. This finding provides a further rationale to avoid transferring excessive numbers of preembryos after in vitro fertilization.