Fetal Station in Second-Stage Arrest of Descent
In a fully dilated second stage with arrest of descent, the fetal head station is typically at or above the ischial spines (station 0 or higher), indicating inadequate descent and a high-risk scenario for operative delivery complications.
Expected Station at Full Dilation
- Normal fetal descent during the deceleration phase (8–9 cm to full dilation) should bring the fetal head to +1 to +2 station. 1
- Terminal cervical dilation cannot be achieved without concurrent fetal descent—the two processes are interdependent. 1, 2
- When full dilation is reached with the fetal head still at or above the ischial spines (station 0 or higher), this signals failure of the normal descent mechanism and raises immediate concern for cephalopelvic disproportion. 3, 2
Station Classification and Clinical Implications
- Station 0 (at the ischial spines): The fetal head is at the level of the ischial spines; this represents inadequate descent for the second stage and is associated with substantially prolonged labor. 4, 5
- Station < 0 (above the ischial spines): The fetal head remains above the ischial spines; this carries a 32.9-fold increased risk of prolonged second stage compared to station at the pelvic floor. 4
- Station between 0 and the pelvic floor: The fetal head is below the ischial spines but not yet at the pelvic floor; this carries a 13.1-fold increased risk of prolonged second stage. 4
Arrest of Descent: Key Warning Signs
- A prolonged deceleration phase combined with failure of descent at full dilation is a strong predictor of cephalopelvic disproportion, second-stage abnormalities, and shoulder dystocia if vaginal delivery is attempted. 3, 2
- Fetal head station at the diagnosis of the second stage is independently and significantly associated with both the duration of the second stage and the risk of operative delivery in a dose-dependent pattern. 5
- When the fetal head is at or above the ischial spines at full dilation, the risk of operative delivery increases substantially, and cesarean delivery should be strongly considered rather than prolonged attempts at vaginal delivery. 2, 5
Assessment Techniques
- Clinical vaginal examination remains the standard for assessing station, but it is subjective and may be inaccurate, especially with caput formation or molding. 6
- Transperineal ultrasound (angle of progression) correlates with fetal station: station 0 corresponds to approximately a 120° angle of progression. 7, 6
- Transabdominal ultrasound (suprapubic descent angle) assesses the proximal part of the fetal skull and is particularly useful when molding is present, as it reflects the true descent of the largest diameter of the skull. 8
Clinical Decision-Making
- Cesarean delivery is justified when there is compelling clinical evidence of cephalopelvic disproportion (such as arrest of descent at station 0 or higher) and the patient has undergone adequate oxytocin augmentation (minimum 4–6 hours of sustained adequate contractions). 1
- Operative vaginal delivery should only be attempted when the fetal head is engaged (at least station 0) and its lowermost part is at or below the ischial spines; attempting delivery with the head above this level carries significant maternal and fetal risks. 9, 8
- Cesarean delivery in the second stage with an impacted fetal head carries greater maternal morbidity (uterine extensions, hemorrhage, infection) and neonatal morbidity (fractures from "pull" methods) than operative vaginal delivery performed at appropriate station. 9
Common Pitfalls to Avoid
- Do not assume adequate descent based solely on full cervical dilation—always assess fetal station independently. 1, 2
- Do not attempt operative vaginal delivery when the fetal head is at or above the ischial spines, as this significantly increases the risk of failed delivery and subsequent complicated cesarean. 9, 5
- Do not overlook the warning sign of a prolonged deceleration phase, which strongly predicts arrest of descent and cephalopelvic disproportion. 3, 2