(399) Risks factors of perinatal morbidity after instrumental delivery among nulliparous women

Instrumental vaginal delivery is a common practice, especially among nulliparous women, and may increase the risk of neonatal morbidity. However, there is a paucity of recent data regarding the risk factors for neonatal morbidity in this context. The goal is to identify risk factors of neonatal morbidity during instrumental vaginal deliveries among nulliparous women.

Study Design: This is an ancillary study of the prospective cohort study INSTRUMODA, the aim of which was to evaluate the protective effect of episiotomy on anal sphincter injury among nulliparous women during instrumental vaginal delivery. This study was conducted in 111 maternity units in France between April 2021 and March 2022. Instrumental deliveries were included from 34 weeks of gestation. Our primary outcome was a composite criterion of neonatal morbidity, including: Apgar score < 7 at 5 minutes, pH < 7.10, neonatal intensive care unit admission, hypothermia therapy, peripartum death, and cephalic or upper-limb trauma. The association between potential risk factors and perinatal morbidity was assessed using logistic regression, accounting for a center effect. Imputation was performed for missing data.

Results: A total of 11,938 instrumental deliveries were included. The primary outcome was observed in 16.9% of deliveries (table 1). Increased perinatal morbidity was associated with sequential instrument use (aOR = 1.50, 95% CI = 1.26 – 1.76), occiput posterior position (a OR = 1.30, 95% CI = 1.07 – 1.58), and delivery between 8 PM and 8 AM (aOR = 1.16, 95% CI = 1.05 – 1.29) (table 2). There was no significant difference in neonatal morbidity related to the type of instrument used (vacuum or forceps) or associated obstetric pathology (macrosomia, preeclampsia, IUGR).

Conclusion:

Sequential use of instruments, occiput posterior fetal position, and deliveries occurring during night shifts are risk factors of neonatal morbidity in case of instrumental vaginal births among nulliparous women. However, neither the type of instrument nor associated obstetric pathology influence neonatal morbidity.