Materials and Methods

We conducted a RCT to investigate the effects of stylette use on catheter insertion outcomes. The trial was approved by the local institutional review board (number 13-46E). The study population included all women aged ≥ 18 years who presented for induction of labor to Aurora Sinai Medical Center during June 2013 through December 2014.

Inclusion in the study further required that women were cared for by obstetrician/gynecologist residents postgraduate year (PGY) 2–4, induced via Foley catheter bulb, had a singleton pregnancy, had intact membranes, and had cephalic presentation. We excluded women cared for by PGY1 residents to ensure that residents within the study already had catheter placement experience. We estimated that residents placed 30 transcervical catheters during PGY1.

We designed our study for the comparison of outcomes between 2 groups. The treatment group was defined as women who received the Foley catheter via digital placement with a stylette and the control group was defined as women who received the catheter via digital placement without a stylette. We powered our study for the detection of difference in insertion time. A sample size of 64 women per group (128 women total) was determined necessary to detect a difference in mean catheter insertion time of 0.5 minutes with normally distributed responses, SD of 1, alpha of 0.05, and power of 0.80.

We also considered a log normal distribution for highly right-skewed responses with similar parameters and found that 58 women per group (116 women total) were needed. Ultimately we targeted the greater of the 2 sample size estimates and randomly assigned women to treatment and control groups using a computer-generated sequence of group identifiers with a 1:1 allocation. For application in the clinical setting, treatment and control group identifiers were concealed within envelopes and available per woman, following consent by a resident physician or research coordinator, in the same sequence as generated.

Women were positioned in the dorsal lithotomy position in the labor bed with feet on stirrups and bottom of bed detached. All inductions used a 22 French Foley catheter and a 5 French stylette if within the stylette group. After insertion, the catheter was filled with 50 mL of water and tugged back against the internal ostium until snug; the tail was then taped to the inside thigh under tension.

The primary outcomes of interest in this study depended on this protocol and included recording insertion time (total minutes to successful catheter placement), patient-assessed pain level (scale of 0–10), and failure of the insertion technique used. Using a stopwatch operated by a nurse in the room, measurement of insertion time began when the provider’s fingers entered the vagina and ended at full inflation of the catheter balloon. Pain level was determined by verbally asking patients to assess their pain following taping of the catheter tail.

Failure was defined as inadvertent amniotomy, excessive time in placement (subjectively determined by the provider placing the catheter), or excessive patient pain (subjectively determined by the provider but based on patient response).

Variables hypothesized as potential confounders of the stylette effect on these primary outcomes included age, race/ethnicity, body mass index, nulliparity, gravidity, history of vaginal delivery and cesarean delivery, gestational age, cervical dilation, admission Bishop score, indication for induction, and PGY of the performing resident physician.

To describe our study population and assess equivalency in characteristics between the treatment and control groups, we computed frequencies and means with 95% confidence intervals (CI), as appropriate per variable type. Differences in proportions and means between the groups were tested using a Pearson’s χ ² test of independence and a Student t test (or Wilcoxon’s rank sum test), respectively. In all cases, test assumptions of sample independence and normality (of original or transformed data) were satisfied.

We examined the effects of the stylette use by testing for treatment-control differences in mean insertion time (natural log transformed) and patient-assessed pain level using a Student t test and in odds of insertion failure using a Pearson’s χ ² test of independence. For each outcome of interest, we also constructed four regression models to examine the fixed main and interaction effects of stylette use and 1 covariate. Models tested the significance of stylette use while adjusting for other variable effects.

Covariates in the 4 models included nulliparity (nulliparous vs multiparous), a history of vaginal delivery (yes vs no), cervical dilation at presentation (centimeters), and resident PGY (2 vs 3 vs 4). Response distributions included the log normal (normal distribution with natural log-transformed response) for catheter insertion time, multinomial for pain level, and binomial for insertion failure. Following backtransformation or exponentiation of parameter estimates, model results were interpreted as the percentage change in insertion time, ratio of odds of less pain, and ratio of odds of failure of the insertion technique used. Unobserved outcome heterogeneity was captured by individual resident physicians, each of which defined a separate random variable and intercept in the model.

To display the statistically significant effects revealed in the regression models, as well as highlight nonsignificant trends, we summarized catheter insertion outcomes overall by use of stylette and by stylette use within confounder subgroup. Basic descriptive statistics, box-and-whisker plots, and bar plots were used. Descriptive statistics included mean with 95% CI, coefficient of variation (SD divided by the mean), and median with interquartile range (IQR), as appropriate per response variable. We performed all analyses using SAS statistical software (version 9.4; SAS Institute Inc, Cary, NC). In all cases, P < .05 was considered statistically significant.

Results

During the study period, there were a total of 3802 deliveries of which 1067 were inductions. A total of 194 Foley catheters were used for cervical ripening in women who met inclusion criteria ( Figure 1 ). Women were principally excluded because of the requirement of catheter placement by obstetrician/gynecologist residents of PGY2–4. We included only these providers to homogenize the clinical experience of the participating providers.

Flow chart of subject inclusion, randomization, and reasons for exclusion

Most women were not eligible for the study because catheters were placed by providers other than second-, third-, and fourth-year obstetric-gynecology residents.

Forgie et al. Effects of stylette for Foley catheter placement. Am J Obstet Gynecol 2016 .

Twenty-nine women declined to participate, and 31 women were excluded for undocumented reasons. Overall, 134 women were consented and randomized, with 11 women subsequently excluded from the study by the institutional review board. A total of 123 total women entered statistical analysis.

Women who received the Foley catheter with a stylette (n = 62) vs without a stylette (n = 61) did not differ by age, race/ethnicity, body mass index, nulliparity, gravidity, history of vaginal delivery or cesarean delivery, gestational age, cervical dilation, admission Bishop score, indication for induction, resident PGY, route of delivery, or chorioamnionitis ( Table 1 ).

No significant differences between the treatment and control groups were detected in log-transformed insertion time ( t ₁₀₅ = 0.38; P = .70), patient-assessed pain level ( t ₁₂₀ = 0.88; P = .38), or odds of insertion failure (χ ² = 0.33; P = .57; Table 2 ). Across all random-intercepts models, no significant interaction effects were detected ( Table 3 ).

Table 3

Measures of effects in models of insertion time, patient pain level, and failure of the insertion method used

Model and explanatory variables	Insertion time		Patient pain level		Failure of insertion method
	Effect size a	P value	Effect size b	P value	Effect size c	P value
Model 1
Stylette
Stylette	1.92 (–19.3 to 28.8)	.87	1.36 (0.72–2.56)	.34	0.75 (0.25–2.27)	.61
No stylette	Reference		Reference		Reference
Nulliparous
Nulliparous	0.17 (–20.6 to 26.3)	.99	0.99 (0.53–1.86)	.98	1.25 (0.42–3.77)	.69
Multiparous	Reference		Reference		Reference
Interaction d		.80		.14		.73
Model 2
Stylette
Stylette	1.99 (–19.3 to 28.9)	.87	1.36 (0.72–2.56)	.34	0.76 (0.25–2.29)	.62
No stylette	Reference		Reference		Reference
History of vaginal delivery
Yes	–2.59 (–22.9 to 23.0)	.82	1.03 (0.55–1.93)	.92	0.80 (0.26–2.41)	.68
No	Reference		Reference		Reference
Interaction d		.63		.12		.89
Model 3
Stylette
Stylette	–0.52 (–20.7 to 24.8)	.96	1.37 (0.72–2.58)	.33	0.70 (0.22–2.25)	.55
No stylette	Reference		Reference		Reference
Cervical dilation	–20.8 (–34.2 to –4.67)	.01	0.65 (0.39–1.08)	.09	0.29 (0.10–0.86)	.03
Interaction d		.35		.35		.75
Model 4
Stylette
Stylette	0.61 (–19.8 to 26.2)	.96	1.35 (0.71–2.54)	.36	0.75 (0.25–2.27)	.61
No stylette	Reference		Reference		Reference
Resident year
PGY2	Reference		Reference		Reference
PGY3	–33.7 (–58.9 to 6.93)	.09	1.20 (0.51–2.87)	.36	0.33 (0.05–2.02)	.23
PGY4	–51.0 (–69.0 to –22.7)	.003	1.09 (0.54–2.21)	.91	0.41 (0.11–1.56)	.19
Interaction d		.35		.10		1.00

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