How do you document fetal station?

Am J Perinatol. Author manuscript; available in PMC 2014 Jul 10.

Published in final edited form as:

PMCID: PMC4091771

NIHMSID: NIHMS609348

Sally Y. Segel, M.D.,1 Carlos A. Carreño, M.D.,2 Steven J. Weiner, M.S.,15 Steven L. Bloom, M.D.,3 Catherine Y. Spong, M.D.,16 Michael W. Varner, M.D.,4 Dwight J. Rouse, M.D.,5 Steve N. Caritis, M.D.,6 William A. Grobman, M.D.,7 Yoram Sorokin, M.D.,8 Anthony Sciscione, D.O.,9 Brian M. Mercer, M.D.,10 John M. Thorp, M.D.,11 Fergal D. Malone, M.D.,12 Margaret Harper, M.D., M.S.,13 Jay D. Iams, M.D.,14 and Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network

Abstract

Objective

To study the relationship between fetal station and successful vaginal delivery in nulliparous women.

Study Design

This was a secondary analysis from a previously reported trial of pulse oximetry. Vaginal delivery rates were evaluated and compared with respect to the fetal station. Spontaneous labor and induction of labor groups were evaluated separately. Multivariable logistic regression analysis was performed to adjust for confounding factors.

Results

Successful vaginal delivery was more frequent with an engaged vertex for spontaneous labor [86.2% versus 78.6%; p = 0.01] and induced labor [87.7% versus 66.1%; p < 0.01]. After adjustment, engaged fetal vertex was not associated with vaginal delivery for spontaneous labor [odds ratio [OR] 1.5; 95% confidence interval [CI] 0.95 to 2.3; p = 0.08] or for women with induced labor [OR 2.2; 95% CI 0.96 to 5.1; p = 0.06].

Conclusion

Among nulliparous women enrolled in the FOX randomized trial in spontaneous labor or for labor induction, an engaged fetal vertex does not affect their vaginal delivery rate.

Keywords: labor, fetal station, vaginal delivery

In early studies by Friedman and Sachtleben, a high fetal station on presentation was associated with a dysfunctional labor pattern.1–4 Subsequent studies examined the relationship between fetal station and cesarean delivery and demonstrated that an unengaged vertex at the time of active labor is associated with a significantly increased chance of cesarean delivery.4–7 Yet, the relevance of these findings to the present day is uncertain as obstetric practice has been characterized by a decreased frequency of operative vaginal delivery and an increased frequency of cesarean delivery.8 The demographic characteristics of reproductive-aged women in the United States have also changed such that the pregnant women are more likely to be older and have a greater body mass index [BMI].9,10 Both of these factors have been linked to higher rates of cesarean delivery.11–13

Thus, in the context of the present obstetric population and the approach to medical care, the relationship between station at admission for labor and vaginal delivery remains uncertain. This secondary analysis of detailed labor data from the modern era was performed to estimate the association between fetal station at admission and subsequent vaginal delivery.

Methods

We conducted a secondary analysis of data derived from a randomized clinical trial of fetal pulse oximetry, in which the 14 clinical centers of Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal Fetal Medicine Units Network14 participated. Nulliparous women ≥36 weeks' gestation with a singleton fetus who presented to labor and delivery between May 2002 and February 2005 were offered enrollment in the study. Those who consented were randomized when their cervical dilation was between 2 and 6 cm and the fetal vertex had reached −1 station. Randomization was performed by a research nurse through an encrypted program in a laptop computer. Women were excluded if they had a temperature > 38°C, HIV, hepatitis, diabetes mellitus, or maternal cardiac or renal disease. Women with hypertensive disorders were not excluded and were eligible for participation in the study and this analysis. The study was approved by the institutional review board at each center, and written informed consent was obtained from all study participants prior to enrollment.

Trained research nurses who were present and managing the pulse oximeter collected the labor and delivery data. For women who presented in spontaneous labor, fetal station was defined as that determined by the examination upon admission to labor and delivery. For women who presented for an induction of labor, fetal station was defined as that determined by the first examination at the time of induction. Women were excluded from analysis if no examination was recorded within 30 minutes of admission for spontaneous labor or at the initiation of their labor induction. Depending on the clinical center, fetal station was recorded based either on the −5 to +5 scale or the −3 to +3 scale. Acknowledging the recommendation of the American Congress of Obstetricians and Gynecologists for using −5 to +5 scale, simple clinical conversion was only possible from the −5 to +5 scale to the −3 to +3 scale. As a result, −5 to +5 station data were converted to the −3 to +3 scale for the purposes of this analysis [►Table 1]. This decision was made prior to beginning the analysis.

Table 1

Conversion of the −5 to +5 Scale to −3 to +3 Scale

Fetal station was analyzed both as an ordinal and dichotomous variable. Because the number of cases with station at +1 and +2 was small, these two groups were combined for analyses utilizing station as an ordinal variable. The association of fetal station with vaginal delivery was evaluated using the Mantel-Haenszel chi-square test for trend, and with time to delivery using the Jonckheere-Terpstra test for trend. For the dichotomous analyses, station was categorized according to whether the fetal vertex was engaged, defined as station 0 or below. The association of dichotomous fetal station with vaginal delivery was evaluated using the chi-square test and with time to delivery using the Wilcoxon rank sum test.

Women who presented in spontaneous labor and women who presented for an induction of labor were analyzed separately. Women in spontaneous labor were further divided according to whether their cervical dilation was ≥4 cm or