Predicting operative vaginal birth through ultrasound


In a recent study, different intrapartum transperineal ultrasound methods showed improved accuracy when predicting failed or complicated operative vaginal birth.

Predicting operative vaginal birth through ultrasound | Image Credit: © zayacsk - © zayacsk -

Predicting operative vaginal birth through ultrasound | Image Credit: © zayacsk - © zayacsk -

Ultrasound (US) is more accurate at predicting failed or complicated operative vaginal birth (OVB) than standard methods, according to a recent study published in the American Journal of Obstetrics & Gynecology.

Increased maternal and neonatal morbidity and mortality risks have been observed following OVB, making accurate knowledge of fetal head descent and position a prerequisite for the operation to improve patient safety. This information is usually obtained through vaginal examination, but this method is often unreliable because of a lack of accuracy, poor rates of predicting complication or failure, and poor interobserver reliability.

A rise in US use for labor assessment has been observed, with intrapartum transperineal ultrasound (ITU) suggested as a method of measuring fetal head descent with increased accuracy. This method allows key landmarks to be identified, creating more opportunities to proxy measure fetal head descent.

Objective measurements of progression distance (PD), head direction (HD), head-symphysis distance (HSD), and angle of progression (AOP) may be accomplished through ITU. However, there is little data on which ITU measures reach this accuracy. Using and understanding measures of high-risk OVB could help clinicians decide whether to proceed with the operation.

To compare the prognostic accuracy of different ITU measures of fetal head descent for predicting complicated or failed OVBs, investigators conducted a systematic review and comparative meta-analysis. Databases were searched for literature from inception to June 10, 2022.

Databases searched included Medline, Embase, CINAHL, and Scopus. Terms used for searches include, “intrapartum,” “transperineal,” “fetal head descent,” “angle of progression,” “head symphysis distance,” “ultrasonography,” “progression distance,” “midline angle,” “head direction,” “head perineum distance,”“forceps,” “operative vaginal,” and “vacuum birth.”

Studies assessing head-perineum distance (HPD), midline angle (MLA), AOP, HD, PD, and HSD were eligible for inclusion. Measurement had to occur prior to OVB, with data about rates of subsequent complicated or failed OVBs available. 

Excluded literature included systematic reviews, literature reviews, letters, editorials, conference abstracts, meta-analyses, study protocols, commentaries, guidelines, and unpublished manuscripts.

Study screening was performed by 2 independent reviewers, with disagreement resolved by a third reviewer. Data extraction was also performed by 2 independent reviewers, with data extracted including study characteristics, population characteristics, ITU measures, definitions of failed and complicated OVB, ITU method, and US cutoff values.

Two independent reviewers used the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) assessment tool to evaluate risk of bias. There are 4 domains in the QUADAS-2: index test, patient selection, flow and timing, and reference standard.

There were 16 studies included in the final analysis. AOP was evaluated in 9 of the studies, HD in 6, MLA in 4, HPD in 8, and PD in 3. Of the 16 studies, none contained sufficient data on HSD. Twelve of the studies were prospective cohort studies, 3 were retrospective cohort studies, and 1 was a case series.

The studies included 2848 women undergoing OVB, 15.4% of which were failed or complicated and 84.6% of which were successful or uncomplicated. Risk of bias was found in all studies, with common reasons for bias risk including limiting participant inclusion, a lack of blinding to ITU results, and a subjective component in the reference standard definition of complicated OVB.

A mean −16.90° difference in APO at rest was measured in women with complicated OVBs compared to those without complicated OVBs. In these groups, the mean MLA difference was 20.00° at rest, the mean HPD difference 5.57 mm at rest, and the mean PD was −10.42 mm at rest. Means were unable to be compared for HD.

Higher area under the receiver operating characteristic curve measures were seen when taken with pushing rather than at rest, with MLA measurements showing the greatest differences. However, these measures were not clinically significant.

Failed OVB was predicted more accurately than complicated OVB by HPD. Higher accuracy for predicting complicated OVB was seen from AOP and HD, but these measures were not clinically significant. A significant increase in prediction accuracy for complicated OVG was seen from AOP and PD compared to HPD.

Overall, these results indicated improved accuracy of failed or complicated OVB through ITU. Investigators recommended clinicians use this information when discussing the idea of performing OVB with women.


Skinner SM, Giles-Clark HJ, Higgins C, Mol BW, Rolnik DL. Prognostic accuracy of ultrasound measures of fetal head descent to predict outcome of operative vaginal birth: a comparative systematic review and meta-analysis. American Journal of Obstetrics & Gynecology. 2023:229(1):10-22. doi:10.1016/j.ajog.2022.11.1294

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