The diagnosis of fetal head engagement: Transperineal ultrasound, a new useful tool?

Objective. - Assessment of fetal head engagement by digital examination is highly subjective even though this method remains the gold standard. Ultrasonography could be helpful to determine fetal head engagement during the second stage of labor. Patients and methods. - Prospective unicentric study to compare the diagnostic of fetal head orientation and engagement between digital examination and ultrasonography. One hundred measurements were performed in 100 patients at complete cervical dilatation. Results. - In 80 % of patients, abdominal ultrasound assessments were consistent with digital examinations in depicting fetal head position. We were not able to evaluate engagement by abdominal ultrasonography. Perineum to fetal head distance was measured between 12 and 83 mm by translabial ultrasonography. When the head was not engaged (-1), the mean distance was 66.4 +/- 7.53 mm. The measure was 56.15 +/- 10.86 mm when the head was at the upper part of the birth canal (+1), 46.47 +/- 12.49 mm at the middle part (+2) and 35.81 +/- 10.42 mm at the lower part (+3: +4). A threshold of 55 mm was associated with a sensibility and a negative predictive value of 100 % for vaginal birth. Discussion and conclusion. Abdominal intrapartum ultrasound increases the accuracy of fetal head position assessment. Translabial ultrasound is a simple and easy method to define fetal head engagement by measuring the distance between perineum and fetal head. Ultrasound during the second stage of labor may serve as an educational tool for physicians in training. (C) 2011 Elsevier Masson SAS. All rights reserved.