Conclusions
We have clarified the mediating and interaction effects of gestational age on labour outcomes for pregnancies complicated by SGA in this causal mediation analysis. The impact of gestational age on caesarean delivery without TOL was profound across gestation. Approximately two-third of all caesareans were performed prelabour. With appropriate counseling, providers may feel comfortable offering TOL to these patients, optimally at 39-40 weeks’ gestation.
Rates of caesarean delivery are increased among SGA after a TOL compared to AGA births at preterm and term gestations, but the effect of gestational age is different. An interaction between gestational age and SGA drives the risk at preterm gestations whereas exposure to SGA alone, likely a consequence of IPD, drives this risk at term. These findings suggest different strategies are needed to maximize vaginal delivery rates for SGA pregnancies who undergo TOL, but it is likely that timing the delivery at term and avoidance of late term gestation would have positive impact.
Acknowledgments : none
Disclosures of interest : Both authors declare no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.