Table 2.

Perineometry Results for 666 Women by Maternal and Obstetric Characteristics

		Peak Pressure (cm H2O), Averaged Over Two Contractions		Duration (sec)†, Averaged Over Two Contractions
Characteristic*	n	Median (IQR)	P‡	Median (IQR)	P‡
Age older than 40 y			.937		.754
Yes	380	30 (19–45)		9 (5–15)
No	286	30 (18–46)		9 (5–16)
Primary race			.118		.121
White or other	594	31 (19–46)		9 (5–16)
African American	72	28 (16–37)		8 (4–13)
Maternal age older than 35 y at first delivery			.340		.068
Yes	199	28 (18–43)		8 (4–13)
No	467	31 (19–46)		10 (5–17)
Multiparous			.590		.389
Yes	493	31 (18–46)		9 (5–15)
No	173	29 (18–44)		9 (5–16)
Body mass index 30 kg/m2 or higher			.175		.892
Yes	163	31 (21–48)		9 (5–15)
No	503	30 (18–45)		9 (5–16)
Obstetric exposure group			<.001		<.001
Unlabored cesarean	131	39 (24–50)		10 (6–16)
Active-labor cesarean	150	36 (23–52)		10 (6–21)
Cesarean after complete dilation	81	35 (23–48)		10 (6–19)
Spontaneous vaginal delivery	225	27 (17–39)		7 (4–14)
Vacuum delivery	30	25 (14–31)		8 (5–14)
Forceps delivery	49	14 (9–23)		4 (3–11)
Prolonged second stage§			.009		.113
Yes	158	27 (15–42)		8 (4–13)
No	508	31 (19–46)		9 (5–16)
Macrosomia at vaginal delivery‖			<.001		.001
Yes	47	20 (11–31)		6 (3–11)
No	619	31 (19–46)		9 (5–16)
Perineal laceration‖			<.001		.017
Yes	183	25 (14–37)		7 (4–14)
No	483	33 (21–48)		9 (5–16)
Episiotomy‖			<.001		<.001
Yes	171	23 (13–34)		6 (3–12)
No	495	33 (21–49)		10 (5–17)
Anal sphincter laceration‖			<.001		.039
Yes	57	21 (12–30)		7 (4–12)
No	609	31 (20–46)		9 (5–16)
No. of vaginal deliveries			<.001		<.001
0	362	36 (24–51)		10 (6–18)
1	107	26 (15–38)		8 (4–15)
2	147	25 (14–37)		7 (4–13)
3 or more	50	21 (13–31)		6 (3–12)

IQR, interquartile range.

^*As measured at the time of muscle strength test, unless otherwise noted.

^†Duration data were missing for four women.

^‡Kruskal-Wallis test.

^§Among those who experienced the second stage of labor at least once.

^‖Among those who experienced at least one vaginal delivery.