Interpretation (in light of other evidence)
Non-occiput anterior (transverse or posterior) positions are associated with a high risk of cesarean section, operative vaginal delivery and other peripartum complications, including third- or fourth-degree perineal lacerations, postpartum hemorrhage and chorioamnionitis13, 18, 40, 41. Compared with neonates born in the OA position, neonates born in a non-occiput anterior position have a lower Apgar score, a higher risk of neonatal intensive care unit admissions and higher rates of birth trauma 18, 19. The incidence of persistent OP position is between 5% and 12% 12, 18, 42, and that of persistent OT position varies from 3% to 8%13, 40, 43. A study by Petitjean et al. 44 identified oxytocin augmentation, excessive gestational weight gain, direct OP position and macrosomia as independent factors associated with non-OA to OA rotation during the first stage of labor. In our study, maternal height is the single individual factor associated with internal fetal occiput rotation. On the other hand, the degree of fetal head rotation, as measured by the MLA, was parallel between vaginal and cesarean delivery groups at first. However, the MLA of the women who experienced vaginal delivery was narrower subsequently, indicating the occurrence of spontaneous rotation.
Moreover, we develop a simple model based on the intrapartum sonographic parameter and maternal characteristic to predict spontaneous fetal head rotation in the first stage of labor. We think this finding might provide the clinicians an opportunity to take earlier action to reduce the obstetric complications associated with persistent OP and OT positions.
Accumulating studies showed that maternal and neonatal characteristics, including parity, maternal age, height, BMI, neonatal birth weight and fetal head position, are independent factors that affect the mode of delivery 28, 45, 46. Burke et al. 47reported a risk prediction model for cesarean delivery using five parameters (maternal age, height, BMI, fetal head circumference and fetal abdominal circumference), with excellent discrimination (Kolmogorov- Smirnov, D statistic, 0.29; 95% CI, 0.28- 0.30). Furthermore, Eggebø et al. 39introduced intrapartum ultrasound to developed another risk score based on maternal characteristics (gestational age, maternal weight, BMI and cervical dilatation), occiput position and intrapartum findings (head perineal distance and caput succedaneum) to predict vaginal birth, which yielded an AUC of 0.853 (95%CI, 0.678-1.000). Our study illustrated a much simple prediction model based on only two parameters (maternal stature and AoP) for evaluating the delivery mode in the nulliparas in the first stage of labor. We started the intrapartum ultrasound assessment during the latent phase (cervical dilatation less than 6 cm), which allowed clinicians to identify early the women who required cesarean delivery. We caution that the knowledge derived from our model should not alter obstetric decision making. However, our study might provide useful information about the chance of spontaneous rotation and vaginal birth, allowing appropriate interventions at the proper time.
CONCLUSION
In conclusion, our study provides simple models based on maternal characteristics and intrapartum ultrasound findings that can predict the chance of vaginal birth and successful internal fetal head rotation in nulliparous women. We suppose these models can be implemented in any delivery unit.