Expected Pelvic Exam Findings at 39 Weeks About to Give Birth
A patient at 39 weeks gestation who is about to give birth should demonstrate progressive cervical dilation (typically ≥3-4 cm), significant effacement (≥80%), and descent of the fetal presenting part (station 0 or lower), with these findings occurring in the context of regular, effective uterine contractions. 1, 2
Cervical Dilation Expectations
- Cervical dilation of 3-4 cm or greater typically indicates active labor in term patients, though the exact threshold varies and some women may labor with less dilation initially 1, 3
- The rate of cervical dilation in active labor averages approximately 1.5 cm/hour in nulliparous women at term, though this shows considerable variability (median duration at 4 cm dilation is 5.5 hours with a range of 0.8-12.5 hours) 1
- Women with >1 cm dilation at 39 weeks are three times more likely to spontaneously labor within the following week (adjusted hazard ratio 3.1), with 60% entering spontaneous labor compared to only 28% of those with <1 cm dilation 4
- A deceleration phase typically occurs toward the end of active labor at approximately 9 cm dilation 1
Cervical Effacement
- Effacement of ≥80% is a key component of active labor diagnosis when combined with regular contractions and appropriate dilation 1
- Effacement >30% in the early third trimester increases the relative risk of preterm labor by 1.8-4.2 times, suggesting that significant effacement is an important marker of cervical change 5
Fetal Station and Descent
- Station 0 or lower (engagement) indicates the fetal presenting part has descended to the level of the ischial spines, which is expected as labor progresses 2
- Multifactor models that include station measurements show mean absolute errors of 0.512 cm when predicting labor progress, demonstrating the importance of accurate station assessment 2
- Serial suprapubic palpation of the base of the fetal skull should be performed to differentiate true descent from molding 6
Additional Clinical Findings
- Regular uterine contractions occurring every 10 minutes or less, lasting more than 40 seconds, are required to diagnose active labor alongside the cervical findings 1
- The modified Bishop score should be assessed, with a score ≥8 indicating a favorable cervix for vaginal delivery 6, 7
- Membrane status (intact versus ruptured) should be documented 6
Critical Assessment Points
- Cephalopelvimetry assessment is vital to exclude cephalopelvic disproportion (CPD), particularly if malposition or excessive molding is noted, as 40-50% of patients with arrested active phase have concomitant CPD 6
- Fetal position should be documented (occiput anterior is optimal; occiput posterior or transverse positions signal potential difficulty) 6
- Asynclitism and degree of molding should be assessed, as excessive molding may indicate CPD 6
- Maternal factors including diabetes, obesity, and fetal macrosomia increase concern for CPD and should be considered in the overall assessment 6
Common Pitfalls to Avoid
- Do not assume that cervical dilation alone predicts imminent delivery, as the rate of labor progression is highly variable and independent of initial dilation on admission 1
- Avoid confusing molding with true descent; always confirm descent with suprapubic palpation 6
- Do not overlook signs of potential CPD (malposition, excessive molding, lack of descent) even if dilation is progressing, as these significantly increase risk of operative delivery or cesarean section 6