Intrapartum Translabial Ultrasonography Reliability in Comparison With Traditional Digital Examination

The sonographically measured head station, 'ITU station', was measured along the longest visible axis of the fetal head, between the intersections with the infra pubic line and the deepest bony part of the fetal head, subtracting 3 cm for the level of the ischial spines. This parameter is useful to determine the level of engagement of the fetal head and its progression throughout labor.

The labor is divided into a latent phase (stage 0), an active phase (stage 1 and 2), and a third stage defined as the time period between the delivery of the baby and the delivery of the placenta. According to the classic definition, the onset of labor is when regular contractions have been established. The latent phase is characterized by painful contractions and cervical dilatation up to 5 cm in accordance with WHO.

The fetal descent in the birth canal is assessed by vaginal digital examinations and related to the ischial spine. ACOG has defined five stations above (-5) and below (+5) the level of the spine (0 stations). Minus five corresponds to the pelvic inlet, zero to the level of the ischial spine, and plus four corresponds to the pelvic floor.

Traditionally, labor progression has been assessed by digital examination of cervical dilatation and fetal descent. Recent studies, however, dispute these findings and found the clinical examination of fetal descent and position to be unprecise and subjective with a high interobserver variation. Dupuis et al. made an important contribution to this debate when he rigorously assessed the accuracy of station diagnosis with digital examinations. . This study provides evidence that digital assessment of fetal head station is unreliable.

However, a study from 2019 found a good correlation between clinical assessments and ultrasound examinations when only one experienced clinician and one trained ultrasound examiner compared their results.