Diagnosis of station and rotation of the fetal head in the second stage of labor with intrapartum translabial ultrasound.

OBJECTIVE

To investigate the ability of intrapartum translabial sonography to diagnose fetal station in the second stage of labor.

METHODS

Patients with uncomplicated pregnancies at term gestation with fetuses in vertex presentation in the second stage of labor underwent serial translabial sonography and digital examinations. In a sagittal section of the maternal pelvis, the direction of the head was noted and categorized as downward, horizontal or upward. By rotating the transducer in the transverse plane the cerebral midline echo was also visualized and the rotation of the head was noted. Clinical and ultrasound data were compared using Somer's d-test.

RESULTS

Sixty patients underwent a total of 168 clinical and sonographic examinations. When on the sonogram the fetal head was directed downward, the station assessed clinically was most frequently <or= + 1 cm from the ischial spines (44/57 (77.2%) cases); when the direction was horizontal, the station was most frequently <or= + 2 cm (53/59 (89.8%) cases); when the fetal head was directed upward, the station was usually >or= + 3 cm (46/52 (88.5%) cases). Failure to visualize the cerebral midline or a rotation >or= 45 degrees were associated with a station of + 2 cm or less in 98/103 (95.1%) examinations. Conversely, a rotation of < 45 degrees was associated with a station of + 3 cm or more in 45/65 (69.2%) examinations. All comparisons between clinical and sonographic findings demonstrated a statistically significant relationship (P < 0.0001). The probability of a station + 3 cm or more was particularly high when an upward direction of the head was seen in combination with a rotation of < 45 degrees (40/42 (95.2%) examinations). The interobserver variability (Cohen's kappa 0.795 and 0.727 for station and rotation, respectively; P < 0.001) and intraobserver variability (0.845 for both station and rotation, P < 0.001) suggested good reproducibility of the method.

CONCLUSIONS

Translabial sonography allows a diagnosis of fetal station with an accuracy comparable to that of digital examination and may provide useful information for diagnosing obstructed labor in the second stage as well as assisting in the choice of instrumental delivery.