Subpubic Arch Angle and Mode of Delivery in Low-Risk Nulliparous Women

Abstract

Objective: To assess whether subpubic arch angle (SPA) measurement before labor onset can predict labor outcome among low-risk pregnant women. Methods: 3D ultrasound volume was transperineally acquired from a series of nulliparous women with uncomplicated pregnancy at term before the onset of labor. SPA was measured offline using Oblique View Extended Imaging (OVIX) on each volume performed by an investigator not involved in the clinical management. Labor outcome was prospectively investigated in the whole study group. Results: Overall, 145 women were enrolled in the study. Of these, 83 underwent spontaneous vaginal delivery, whereas obstetric intervention was performed in 62 cases (Cesarean section in 40 and vacuum extraction in 22). The SPA appeared to be significantly narrower in the women submitted to obstetric intervention compared with those undergoing spontaneous vaginal delivery (116.8 ± 10.3° vs. 123.7 ± 9.6°, p < 0.01). At multivariate analysis SPA and maternal age were identified as independent predictors of the mode of delivery. On the other hand, the duration of labor did not show a significant relationship with SPA. Conclusions: In low-risk nulliparous women at term gestation, SPA measurement obtained by 3D ultrasound before the onset of labor seems to predict the likelihood of an obstetric intervention but not the duration of labor.

Association of term isolated microcephaly with mode of delivery and perinatal outcome - a retrospective case-control analysis

“…However, in the present study, the distribution of spontaneous vaginal and vaginal operative deliveries was similar for the microcephalic fetuses and the fetuses with a normal head circumference. This finding suggests that additional factors in labor process may decrease the potential gain of small head circumference, such as a narrow pubic arch angle and small maternal stature, which correlate with a small pelvic diameter [21,22]. Both these factors have been associated with a higher rate of instrumental vaginal delivery.…”

Correlation between Subpubic Arch Angle and Mode of Delivery in Large-for-Gestational-Age Fetuses

“…Within a general population of women with singleton pregnancies close to term, SPA width has shown a normal distribution ranging from 65.6 to 131.6° and a mean value just below 110° [16]. A narrow SPA obtained on 3D ultrasound has been associated with an increase in the incidence of prolonged labor [16], persistent occiput posterior at birth, and UOI among nulliparous women [17,18]. In the current study, in a population at high risk for cephalopelvic disproportion, SPA width was demonstrated to predict an abnormal course of labor with 89% sensitivity and an over 70% positive predictive value.…”

“…Very recently, the use of ultrasound has proved to be reliable in assessing the subpubic arch angle (SPA) [11,12], whose size is related to the transverse diameter of the birth canal [13]. Some independent studies have shown that, in the general population, a narrow SPA at antepartum ultrasound is associated with prolonged labor [14][15][16] and an increased risk of obstetric intervention [17,18]. The aim of our study was to assess the correlation between the SPA and the outcome of labor in a group of women at higher risk for obstructed labor, including nulliparous women with large-for-gestationalage (LGA) neonates.…”

Three-dimensional/four-dimensional transperineal ultrasound: clinical utility and future prospects

“…Despite the strong correlation with adverse obstetrical outcome, it should be highlighted that the accuracy of SPA in the prediction of complications remains limited, 83 , 84 and should not be used alone for clinical decision making.…”

“…The SPA is then measured by the two-line function ( D ) (reproduced from Youssef et al with permission). 84 …”