Fetal head station and head circumference at second‐stage onset and likelihood of vaginal delivery in nulliparous women
Itamar Gilboa, Keren‐Or Wertheimer, Daniel Gabbai, Einat Tako, Anat Lavie, Yariv Yogev, Emmanuel AttaliAbstract
Objective
Our objective was to evaluate the combined association of fetal head station (FHS) at second‐stage onset and fetal head circumference (HC) with the likelihood of spontaneous vaginal delivery (SVD) in nulliparous women.
Methods
This retrospective cohort study included nulliparous women with singleton, vertex‐presenting, term pregnancies (≥37 weeks) who reached the second stage of labor between 2013 and 2023 at a tertiary medical center. FHS was categorized as above, at, or below the ischial spines. HC, measured by ultrasound within 14 days before delivery, was dichotomized as <350 mm or ≥350 mm. Participants were classified into six FHS–HC groups. The primary outcome was SVD. Associations were assessed using multivariable logistic regression.
Results
Among 4230 women, SVD rates ranged from 57.7% for FHS above the ischial spines with HC ≥350 mm to 88.7% for FHS below the ischial spines with HC ≥350 mm. Compared with the reference group (FHS below the ischial spines and HC <350 mm), the adjusted odds of SVD decreased with higher station: adjusted odds ratio (aOR) 0.73 (95% confidence interval [CI] 0.60–0.88) for station at the ischial spines and 0.59 (95% CI 0.44–0.80) for station above the ischial spines. Among women with HC ≥350 mm, those with FHS above the ischial spines had the lowest likelihood of SVD (aOR 0.35; 95% CI 0.14–0.82). Higher FHS and larger HC were associated with longer second‐stage duration ( P < 0.001).
Conclusion
FHS at second‐stage onset was more strongly associated with SVD than was HC. Combined FHS–HC assessment may help identify women at increased likelihood of operative delivery and support closer monitoring of labor progress.