Objective
To investigate the cost-effectiveness of elective induction of labor at 41 weeks in nulliparous women.
Study Design
A decision analytic model comparing induction of labor at 41 weeks vs expectant management with antenatal testing until 42 weeks in nulliparas was designed. Baseline assumptions were derived from the literature as well as from analysis of the National Birth Cohort dataset and included an intrauterine fetal demise rate of 0.12% in the 41st week and a cesarean rate of 27% in women induced at 41 weeks. One-way and multiway sensitivity analyses were conducted to examine the robustness of the findings.
Results
Compared with expectant management, induction of labor is cost-effective with an incremental cost of $10,945 per quality-adjusted life year gained. Induction of labor at 41 weeks also resulted in a lower rate of adverse obstetric outcomes, including neonatal demise, shoulder dystocia, meconium aspiration syndrome, and severe perineal lacerations.
Conclusion
Elective induction of labor at 41 weeks is cost-effective and improves outcomes.
Postterm pregnancy, defined as pregnancy that extends to 42 completed weeks (42 weeks and 0 days) and beyond, is associated with significant risks to the fetus, including perinatal death, meconium staining, macrosomia, low umbilical artery pH, and low 5 minute Apgar score. Postterm pregnancy carries additional maternal risks as well, such as increased rates of severe perineal laceration, labor dystocia, and cesarean delivery. Thus, 42 weeks has been designated by the American College of Obstetricians and Gynecologists as the threshold at which the balance of benefits and risks of intervention favors induction of labor. However, a recent systematic review and a Cochrane review suggest that induction at 41 weeks results in improved perinatal outcomes without increasing the cesarean delivery rate. Additionally, analysis of practice patterns reveals that many obstetricians induce their patients at 41 weeks. Still, induction of labor has associated costs, and for nulliparous women, who are more likely to reach a gestational age of 41 weeks, elective induction of labor may result in an increase in rates of prolonged labor, failed induction, or cesarean delivery.
See Journal Club, page 179
The purpose of the current study was to use decision analysis to investigate the clinical outcomes and cost-effectiveness of elective induction of labor at 41 weeks vs expectant management with antenatal testing until 42 weeks in nulliparous women.
Materials and Methods
A decision analytic model was developed with TreeAgePro 2006 software (Treeage Software Inc, Williamstown, MA) to compare elective induction of labor at 41 weeks of gestation with expectant management with antenatal testing until 42 weeks of gestation. The decision analytic model tracks a hypothetical cohort of nulliparous women with low risk, singleton, cephalic gestations, beginning at 41 weeks of pregnancy. The framework allowed us to compare the expected costs and health benefits of 2 alternative strategies (induction of labor at 41 weeks and expectant management until 42 weeks), while accounting for uncertainty in potential adverse outcomes.
We estimated the probabilities of several pregnancy- and delivery-related events as well as the risk of maternal and/or neonatal mortality and monetary costs, based on the published literature. Women undergoing expectant management could go into spontaneous labor, develop preeclampsia requiring induction of labor, or have an intrauterine fetal demise (IUFD). In addition, women undergoing expectant management were subjected to antenatal testing consisting of a nonstress test and measurement of amniotic fluid volume to assess fetal well-being. Nonreassuring antenatal status was considered as an indication for, and resulted in, labor induction. All women who reached a gestational age of 42 weeks underwent induction of labor at that time ( Figure 1 ).
The probability of different obstetric and neonatal outcomes was modeled as a function of both approach to labor (ie, expectant management vs labor induction) and gestational age at delivery. Neonatal outcomes included the following: (1) IUFD, (2) shoulder dystocia with the possibility of brachial plexus injury or neonatal demise, and (3) meconium aspiration with the possibility of neonatal demise. Maternal outcomes included the following: (1) mode of delivery, including spontaneous vaginal delivery, operative vaginal delivery, or cesarean delivery with potential for maternal mortality as a consequence, and (2) severe perineal laceration, defined as a perineal laceration injuring the anal sphincter. The probability estimates were obtained from the published literature as well as the National Birth Cohort dataset. Baseline probabilities are displayed in Table 1 .
| Variable | Baseline | Low | High | Reference |
|---|---|---|---|---|
| Probability of cesarean delivery | ||||
| Induction of labor | 0.27 | 0.135 | 0.405 | US Birth Cohort, 2003 |
| Spontaneous labor | 0.217 | 0.108 | 0.325 | US Birth Cohort, 2003 |
| RR for cesarean delivery for expectant management vs IOL at 41 wks | 1.0 | 0.7 | 1.50 | Gulmezoglu et al, 2006 |
| Probability of spontaneous labor at 41 wks | 0.52 | 0.26 | 0.78 | Alexander et al, 2001 |
| Probability of IUFD at 41 wks | 0.0012 | 0.0006 | 0.0018 | Smith, 2001 |
| Probability of operative vaginal delivery | ||||
| 42 wks | 0.174 | 0.087 | 0.261 | Caughey et al, 2007 |
| 41 wks | 0.133 | 0.0665 | 0.1995 | Caughey et al, 2007 |
| Probability of epidural | ||||
| Induction of labor | 0.8143 | 0.7198 | 1.0 | UCSF |
| Spontaneous labor | 0.7198 | 0.6 | 1.0 | UCSF |
| Probability of macrosomia | ||||
| 42 wks | 0.15 | 0.075 | 0.225 | Alexander et al, 2000 |
| 41 wks | 0.12 | 0.06 | 0.18 | Alexander et al, 2000 |
| RR for cesarean delivery with macrosomia | 1.52 | 0.81 | 2.43 | Boulet et al, 2003 ; Sanchez-Ramos et al, 2003 |
| Probability of shoulder dystocia | ||||
| Without macrosomia | 0.0065 | 0.00325 | 0.00975 | Nesbitt et al, 1998 ; Rouse et al, 1996 |
| With macrosomia | 0.1 | 0.05 | 0.15 | Nesbitt et al, 1998 |
| RR for shoulder dystocia with operative vaginal delivery | 1.74 | 0.95 | 2.85 | Nesbitt et al, 1998 |
| Probability of shoulder dystocia causing | ||||
| Permanent injury | 0.067 | 0.0335 | 0.1005 | Rouse et al, 1996 |
| Neonatal demise | 0.001 | 0.0005 | 0.0015 | Nesbitt et al, 1998 |
| Probability of meconium-stained fluid | ||||
| 42 wks | 0.277 | 0.1385 | 0.4155 | Sanchez-Ramos et al, 2003 |
| 41 wks | 0.224 | 0.112 | 0.336 | Sanchez-Ramos et al, 2003 |
| Probability of meconium aspiration syndrome | ||||
| 42 wks | 0.032 | 0.016 | 0.048 | Gulmezoglu et al, 2006 |
| 41 wks | 0.008 | 0.004 | 0.012 | Gulmezoglu et al, 2006 |
| Probability of meconium aspiration syndrome causing neonatal demise | 0.00025 | 0.000125 | 0.000375 | Dargaville and Copnell, 2006 |
| Probability of positive NST at 41 wks | 0.14 | 0.07 | 0.21 | Bochner, 1988 |
| Probability of severe perineal laceration | ||||
| 42 wks, vaginal delivery | 0.051 | 0.0255 | 0.0765 | Caughey et al, 2007 |
| 42 wks, operative vaginal delivery | 0.282 | 0.141 | 0.423 | Caughey et al, 2007 |
| 41 wks, vaginal delivery | 0.036 | 0.018 | 0.054 | Caughey et al, 2007 |
| 41 wks, operative vaginal delivery | 0.26 | 0.13 | 0.39 | Caughey et al, 2007 |
| Probability of preeclampsia | ||||
| 42 wks | 0.012 | 0.006 | 0.018 | Caughey et al, 2003 |
| 41 wks | 0.012 | 0.006 | 0.018 | Caughey et al, 2003 |
| Probability of maternal mortality | ||||
| Cesarean delivery | 0.00035 | 0.000175 | 0.000525 | Harper et al, 2003 |
| Vaginal delivery | 0.000092 | 0.000046 | 0.000138 | Harper et al, 2003 |
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