Abstract
Rates of cesarean section increase worldwide, and the components of this increase are partially unknown. A strong role is prescribed to dystocia, and at the same time, the diagnosis of dystocia is highly subjective. Previous studies indicated that risk of cesarean is higher when women are admitted to the hospital early in the labor. We examined data on 1,202 nulliparous women with singleton, vertex pregnancies and spontaneous labor onset. We selected three groups based on cervical dilatation at admission: early (0.5-1.5 cm, N = 178), intermediate (2.5-3.5 cm, N = 320), and late (4.5-5.5 cm, N = 175). The Kaplan-Meier estimator was used to analyze the risk of delivery by cesarean section at a given dilatation, and thin-plate spline regression with a binary outcome (R library gam) to assess the form of the associations between the cesarean section in either the first or second stage versus vaginal delivery and dilatation at admission. Women who were admitted to labor early had a higher risk of delivery by cesarean section (18 versus 4% in the late admission group), while the risk of instrumental delivery did not differ (24 versus 24%). Before 4 cm dilatation, the earlier a woman was admitted to labor, the higher was her risk of delivery by cesarean section. After 4 cm dilatation, however, the relationship disappeared. These patterns were true for both first and second stage cesarean deliveries. Oxytocin use was associated with a higher risk of cesarean section only in the middle group (2.5-3.5 cm dilatation at admission). Early admission to labor was associated with a significantly higher risk of delivery by cesarean section during the first and second stages. Differential effects of oxytocin augmentation depending on dilation at admission may suggest that admission at the early stage of labor is an indicator rather than a risk factor itself, but admission at the intermediate stage (2.5-3.5 cm) becomes a risk factor itself. Further research is needed to study this hypothesis.
Highlights
The high and steadily increasing rates of cesarean section both in the US [1,2,3,4] and worldwide [5] are a cause for concern and provide motivation to study the underlying causes of these patterns
For the observed higher risk of cesarean section among women admitted to labor early, there are two potential explanations: first, the risk is pre-existent and early admission is an indicator of problems during the course of labor and, second, the risk increase occurs during the course of labor, with early admission facilitating a cascade of interventions resulting in cesarean section [37, 44]
They may not respond to the labor stimulation. Since these women may not be in true labor, early admission could be resulting in the diagnosis of dystocia and performance of a cesarean section [9, 17]
Summary
The high and steadily increasing rates of cesarean section both in the US [1,2,3,4] and worldwide [5] are a cause for concern and provide motivation to study the underlying causes of these patterns. Several studies have determined that cesarean rates are higher among women admitted during the early stages of labor (i.e., with early cervical dilatation) than among those who were admitted at a later stage (i.e., with advanced cervical dilatation) [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] The reasons for this association are not clear. Previous studies indicated that risk of cesarean is higher when women are admitted to the hospital early in the labor
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