INTRAPARTUM ULTRASOUND FOR ASSESSMENT OF FETAL PROGRESSION. A Randomized, Controlled, Crossover Clinical Trial to evaluate the variation of AoP or HPD, according to Maternal Position and Pelvis (MaPP Study)

BACKGROUND: The use of ultrasound has been suggested to support the management of labor. According to several studies, ultrasound examination is more accurate and reproducible than clinical examination in diagnosing fetal head position, fetal station, and in the prediction of labour arrest. Furthermore, there is growing evidence that ultrasound in labour may predict the outcome of instrumental vaginal delivery. Several sonographic parameters have been proposed to evaluate the head station. Furthermore, all ultrasound parameters studied so far, have always been measured with the woman in a supine position, while the biomechanics of childbirth with its mechanisms, together with maternal movement, promote fetal rotation and the adaptation of its diameters with those of the maternal pelvis, allowing to gain more room for the fetal descent. Moreover, in most of the studies on intrapartum ultrasound, the mobility of the pelvis has not been mentioned. OBJECTIVES: The study primarily aims to: measure the variation of AoP (“angle of progression”), in case of occipital anterior head position, or HPD (“head perineum distance”), in case of occipital posterior head position, in the supine and kneeling-squat position in the same woman, during the expulsion phase, both at rest and during the push; to evaluate the potential role of the AoP/HPD Delta (difference) as an indicator of pelvic adaptability. The secondary objectives focus on: identifying a relationship between the mobility of the pelvis and different values of AoP/HPD and between pelvis mobility and maternal outcomes at delivery; collecting maternal and neonatal outcomes; identifying a relationship between the mobility of pelvis, AoP and HPD and maternal outcome at delivery; assessing the variation in the anteroposterior diameter of the levator hiatus in spontaneous pushing and the Valsalva maneuver (in the supine and kneeling squat positions), and the investigation on the potential correlation between levator ani co-activation and the duration of the expulsive phase. New cut-offs of AoP/HPD (and their Delta) and predictive capacity of vaginal delivery could be determined in further research. METHODS: This study is designed as a randomized, controlled, crossover clinical trial, multicenter study enrolling pregnant women in the third trimester. The study duration is expected to be 36 months. Women will be enrolled in the third trimester of pregnancy at the Complex Operative Unit of Gynecology and Obstetrics in Padua, Italy, according to the inclusion and exclusion criteria. Participants will firstly sign an informed consent, secondly anamnestic data will be collected and Dynamic External Pelvimetry test will be realized. During labour, data concerning labor progression, midwifery-medical interventions, ultrasound iconography will be collected. During the pushing stage in labor, intrapartum ultrasound by transabdominal and transperineal approach will be performed. Transabdominal ultrasound will be performed to detect fetal head position, fetal spine position and fetal head flexion. Transperineal ultrasound will be carried out to measure AoP (in case of occiput anterior head position) or HPD (in case of occiput posterior head position) in the supine position and kneeling-squat position in the same woman during the expulsion phase, according to the order of REDCap randomization made at the enrollement. Finally, after delivery, within 48 hours, data about maternal and neonatal outcomes will be collected. CONCLUSIONS: In encouraging results, the study will identify a significant variation of ultrasound parameters in the two maternal positions. This could lead to potential new cut-offs predictive of pelvic capacity for vaginal birth. In the clinical practice, the study could be a support for obstetricians and midwives in the management of labour, in order to protect the physiology of birth, by reducing caesarean section’s rate.