OBJECTIVE:To quantify the risk and risk factors for cesarean delivery associated with medical and elective induction of labor in nulliparous women.

METHODS:A prospective cohort study was performed in nulliparous women at term with vertex singleton gestations who had labor induced at 2 obstetrical centers. Medical and elective indications and Bishop scores were recorded before labor induction. Obstetric and neonatal data were analyzed and compared with the results in women with a spontaneous onset of labor. Data were analyzed using univariate and multivariable regression modeling.

RESULTS:A total of 1,389 women were included in the study. The cesarean delivery rate was 12.0% in women with a spontaneous onset of labor (n = 765), 23.4% in women undergoing labor induction for medical reasons (n = 435) (unadjusted odds ratio [OR] 2.24; 95% confidence interval [CI] 1.64-3.06), and 23.8% in women whose labor was electively induced (n = 189) (unadjusted OR 2.29; 95% CI 1.53-3.41). However, after adjusting for the Bishop score at admission, no significant differences in cesarean delivery rates were found among the 3 groups. A Bishop score of 5 or less was a predominant risk factor for a cesarean delivery in all 3 groups (adjusted OR 2.32; 95% CI 1.66-3.25). Other variables with significantly increased risk for cesarean delivery included maternal age of 30 years or older, body mass index of 31 or higher, use of epidural analgesia during the first stage of labor, and birth weight of 3,500 g or higher. In both induction groups, more newborns required neonatal care, more mothers needed a blood transfusion, and the maternal hospital stay was longer.

CONCLUSION:Compared with spontaneous onset of labor, medical and elective induction of labor in nulliparous women at term with a single fetus in cephalic presentation is associated with an increased risk of cesarean delivery, predominantly related to an unfavorable Bishop score at admission.

LEVEL OF EVIDENCE:II-2.

PURPOSE: To ascertain any differences in foetomaternal outcomes in induced and spontaneous labour among nulliparous women delivering at term. METHODS: A retrospective matched cohort study consisting of 403 nulliparous women induced at≥292 days and 806 nulliparous women with spontaneous labour at 285-291 days. RESULTS: Compared to those in spontaneous labour, women who had induction of labour were three times more likely to have a caesarean delivery (OR 3.1, 95% CI 2.4-4.1; P < 0.001). Women who had induction of labour were 2.2 times more likely to have oxytocin augmentation (OR 2.2, 95% CI 1.7-2.8; P < 0.001), 3.6 times more likely to have epidural anaesthesia (OR 3.6, 95% CI 2.8-4.6; P < 0.001), 1.7 times more likely to have uterine hyperstimulation (OR 1.7, 95% CI 1.1-2.6), 2 times more likely to have a suspicious foetal heart rate trace (OR 2.0, 95% CI 1.5-2.6), 4.1 times more likely to have blood loss over 500 ml (OR 4.1, 95% CI 2.9-5.5; P < 0.001), and 2.9 times more likely to stay in hospital beyond 5 days (OR 2.9, 95% CI 1.5-5.6; P < 0.001). Babies born to mothers who had induction of labour were significantly more likely to have an Apgar score of<5 at 5 min and an arterial cord pH of<7.0. CONCLUSION: Compared to those with spontaneous labour, nulliparous women with induced labours are more likely to have uterine hyperstimulation, caesarean delivery, and babies with low Apgar scores. Nulliparous women should be made aware of this, as well as potential risks of expectant management during counseling.

OBJECTIVE:To determine whether changing the definition of the group to which induction is being compared (ie, noninduced delivering during the same week as those induced compared with two definitions of expectant management) changes the association of labor induction and increased cesarean risk.

METHODS:A New York State birth-certificate database was used to estimate odds ratios for cesarean delivery associated with labor induction at term. The analyses used three definitions of controls: cesarean delivery after induction compared with after spontaneous labor by week (week-to-week), induction at a given gestation age compared with expectant management of all other women after gestational age (all above), or induction at a given gestational age compared with expectant management of all other women at or after that gestational age (at or above). Chi-square logistic regression was used for comparisons and adjustment for possible confounders.

RESULTS:All variations of comparison groups were associated with increased unadjusted cesarean risk after induction, although not after 39 weeks in the all-above group. After adjustment, increased risk persisted from 37 to 41 weeks using the week-to-week group and from 38 to 41 weeks in the at-or-above group (odds ratios 1.24 to 1.45) but was no longer significant in the all-above group. The excess cesarean delivery risk associated with labor induction is between 1 and 2 per 25 inductions.

CONCLUSION:Labor induction is associated with increased cesarean risk whether using a week-to-week comparison group or an expectant group that includes women the same week or beyond that of the index induction, even after adjustment for parity, high-risk factors, and demographic variables. Although the magnitude of increased risk for a given woman undergoing induction is not large, women nonetheless should be informed of this increased risk.

LEVEL OF EVIDENCE:II.

OBJECTIVE:To determine whether changing the definition of the group to which induction is being compared (ie, noninduced delivering during the same week as those induced compared with two definitions of expectant management) changes the association of labor induction and increased cesarean risk.

METHODS:A New York State birth-certificate database was used to estimate odds ratios for cesarean delivery associated with labor induction at term. The analyses used three definitions of controls: cesarean delivery after induction compared with after spontaneous labor by week (week-to-week), induction at a given gestation age compared with expectant management of all other women after gestational age (all above), or induction at a given gestational age compared with expectant management of all other women at or after that gestational age (at or above). Chi-square logistic regression was used for comparisons and adjustment for possible confounders.

RESULTS:All variations of comparison groups were associated with increased unadjusted cesarean risk after induction, although not after 39 weeks in the all-above group. After adjustment, increased risk persisted from 37 to 41 weeks using the week-to-week group and from 38 to 41 weeks in the at-or-above group (odds ratios 1.24 to 1.45) but was no longer significant in the all-above group. The excess cesarean delivery risk associated with labor induction is between 1 and 2 per 25 inductions.

CONCLUSION:Labor induction is associated with increased cesarean risk whether using a week-to-week comparison group or an expectant group that includes women the same week or beyond that of the index induction, even after adjustment for parity, high-risk factors, and demographic variables. Although the magnitude of increased risk for a given woman undergoing induction is not large, women nonetheless should be informed of this increased risk.

LEVEL OF EVIDENCE:II.