France: Ultrasound assessment of the head position and station of the fetus before operative vaginal delivery (OVD) can moderately help predict difficult OVD, states a recent study in the Journal of Gynecology Obstetrics and Human Reproduction. Factors associated with difficult OVD include ultrasound assessment of posterior or transverse positions and head perineum distance (HPD) with a threshold of 37 mm (without compression of soft tissue) and 17 mm (with compression).

The study by A.Plurien, CHU Lille, Department of Obstetrics, avenue Eugène Avinée, Lille, France, and colleagues was aimed to evaluate whether ultrasound assessment of fetal head position and station though HPD, is more predictive of a difficult OVD than digital examination in a retrospective, monocentric case control study.
The study included all singleton OVD at ≥34 weeks gestation. The principal criteria for a difficult OVD were based on a composite criterion of: an OVD considered "difficult" by the birth attendant, and/or two vacuum device detachments if a vacuum was used, and/or change of instrument, and/or a cesarean delivery for OVD failure.
A total of two hundred eighty-six OVDs were included, out of which 65 (22.7%) were difficult.
Key findings include of the study include:
The area under the curve (AUC) for predicting difficult OVD according to fetal position from digital examination or ultrasound was 0.62 and 0.66 respectively.
Regarding fetal station, the AUCs of HPD without and with pressure were 0.59 and 0.60 respectively.
Factors associated with difficult OVD were posterior and transverse positions (OR: 2.931), HPD without pressure (threshold of 37 mm, OR: 2.327), and HPD with pressure (threshold of 17 mm, OR: 2.594).
"Our findings revealed that ultrasound can "moderately" help predict if operative vaginal delivery will be difficult by estimating the head position and station of the fetus," wrote the authors. "Ultrasound assessment of posterior or transverse positions and HPD with a threshold of 37 mm (without compression of soft tissue) and 17 mm (with compression) were factors associated with difficult OVD."
"There is a need for future studies focusing on handling ultrasound and better defining its indications and thresholds in specific populations," they concluded.
Reference:
The study titled, "Ultrasound assessment of fetal head position and station before operative delivery: can it predict difficulty?," was published in the Journal of Gynecology Obstetrics and Human Reproduction.
DOI: https://doi.org/10.1016/j.jogoh.2022.102336