Intrapartum ultrasound for the examination of the fetal head position in normal and obstructed labor

Abstract

Objective: To assess the feasibility of transabdominal ultrasound for determining fetal head position in laboring women and compare it to digital examination, and to study ultrasonographically the rotation of the fetal head in normal and obstructed labor.

Design: This was an observational prospective study of 148 women in active labor. Ultrasound examinations were performed longitudinally in the first and second stages of labor.

Results: Assessment of the fetal head position by digital examination was not possible in 60.7% (122/201) of cases in the first stage and 30.8% (41/133) in the second stage of labor. Difficulty in assessing the position was more likely if the occiput was posterior in comparison to anterior and in the maternal right in comparison to the left side. In the second stage, it was three times more likely for the assessment not to be possible digitally if the occiput was posterior. In the cases when assessment by vaginal examination was possible, the correlation with ultrasound was average in the first stage (kappa = 0.59) and good in the second stage (kappa = 0.77). Overall fetal head position assessment by digital examination was accurate in 31.28% of the cases in the first stage and 65.7% of the cases in the second stage of labor. Rotation of the fetal head is highly unlikely when labor begins in the occipital anterior position. Persistent occipital posterior position developed through failure to rotate from an initial occipital posterior or transverse position. Duration of the first stage of labor was independently related to parity and position of the fetal spine at presentation, and duration of the second stage of labor was independently related to parity, birth weight, position of the fetal head at the beginning of the second stage, rotation and position of the head at delivery.

Conclusion: Ultrasound assessment of the fetal head position in labor is feasible in a busy labor ward. Digital examination is less accurate than ultrasound, in particular in cases of obstructed labor when medical intervention is more likely to be needed. Ultrasound assessment may prove useful in the prediction and diagnosis of difficult and prolonged labor.