Neonatal small-for-gestational age status as a favorable factor for the complete vaginal delivery of both fetuses in Japanese dichorionic twins.

Aim: In singletons, neonatal small-for-gestational age (SGA) status is an unfavorable postpartum outcome leading to cesarean section (CS) and increasing the possibility of maternal operative complications. Perinatal characteristics of SGA newborns in dichorionic (DC) twins were investigated for the prognostic impact on their mothers.

Methods: A retrospective study was performed from 2004 to 2009 on 329 DC twins with two live births. Neonates were classified as SGA if they weighed less than the 10th percentile at birth according to Japanese singleton norms. Statistical differences between DC twins delivering appropriate-for-gestational age (AGA)/AGA pairs (control group) and AGA/SGA, SGA/AGA or SGA/SGA pairs (the first/second twins) were analyzed.

Results: The median (range) of the gestational ages at delivery for AGA/AGA, AGA/SGA, SGA/AGA and SGA/SGA pairs were 37.1 (27.1-40.3), 37.2 (29.0-40.9), 37.1 (28.1-40.7) and 37.3 (33.3-40.4) weeks, and the complete vaginal delivery rates of both fetuses were 66.2% (43/65), 84.8% (28/33), 82.4% (14/17) and 70.0% (7/10), respectively. Compared with AGA/AGA pairs, AGA/SGA pairs showed a higher incidence of spontaneous vaginal births of both fetuses (31.3% [26/83] vs 19.9% [37/186], OR 1.84, 95% CI 1.45-4.73) and a lower incidence of emergent CS (25.3% [21/83] vs 38.7% [72/186], OR 0.53, 95% CI 0.30-0.95).

Conclusion: The relatively small size of SGA fetuses allows both fetuses to remain inside the uterus for a longer time and to easily pass through the maternal parturient canal for complete vaginal delivery. Neonatal SGA status is a favorable factor for avoiding operative complications of CS and optimizing maternal perinatal outcomes.