Induction of labor is a valuable obstetric procedure when indicated by a medical or clinical condition. However, strong debate surrounds the issue of non-medical inductions that are conducted for convenience, and whether or not the benefits outweigh the risks. This research focuses on trends in induction and assesses maternal and neonatal outcomes associated with labor induction, specifically those inductions conducted without identifiable medical indications. In this study, Utah birth certificate records from 1992 to 2005 were used to examine trends. Maternal and neonatal outcomes related to the induction of labor without an identified indication were assessed using only 2005 birth certificate data. When comparing neonatal outcomes, induced and non-induced deliveries were quite similar. However, nulliparous women with induced labor were significantly more likely to have instrumental procedures used to assist with vaginal delivery compared to the non-induced group (22.8% vs. 17.7 %). It is the recommendation of this study that women receive a complete disclosure of the risks and benefits associated with the induction of labor before undergoing this obstetric procedure. Future studies are needed to understand why Utah’s induction rate is higher than the national rate.
Induction of labor is a valuable obstetric procedure when initiated for a medical reason. For several clinical conditions, the decision to induce labor may be appropriate and lifesaving for mother and child. Although induction of labor has been practiced for many years, the procedure has become more widely used in recent years. Nationally and in Utah, induction rates doubled between 1992 and 2005. However, large proportions of inductions are performed in the absence of any medical or obstetric indication and are considered “elective.”
According to the American College of Obstetricians and Gynecologists (ACOG), induction of labor is undertaken when, in the opinion of the physician, the risks of delivery to the mother or the fetus or both, are less than the risk of continuing the pregnancy (ACOG, 1999).
Controversy exists regarding the potential benefit of elective induction at term. Proponents of elective induction argue that they are avoiding potential adverse outcomes associated with postdates, preeclampsia and term intrauterine fetal death of unknown causes (Martin et al., 1978). It was suggested by Macer et al. (1992) that elective induction allows for better planning by the physician, patients, and their families. The anxiety of some women may be reduced by the assurance that their personal physician may be present during the birth of their child. Others advocate elective induction to allow for daytime deliveries with a rested patient and optimal perinatal medical care personnel (Smith et al., 1984). Those opposing elective induction would argue that not only is it generally not recommended by ACOG, but also it is an unnecessary and unnatural process (Macer et at., 1992). There is concern over inducing labor before fetal lung maturity has been achieved (ACOG, 1999).
A number of studies have examined the associations between elective induction and pregnancy outcomes. Although inconsistent, the results are compatible with an association between elective induction and increased risk of cesarean delivery. Some studies have observed this increased risk among all women (Prysak et al., 1998; Glantz, 2005) while others have observed it only among nulliparous women (Seyb et al, 1999; Dublin et al, 2000). Many studies have found that patterns of labor progression differ between women who are induced and those who are not (Hoffman et al., 2006; Vahratian et al., 2005). A higher rate of instrumental delivery has also been observed among induced women compared to those experiencing spontaneous labor (Dublin et al., 2000; Smith et al., 1984). Women who were induced tended to receive greater numbers of intrapartum interventions, such as epidural anesthesia, compared to women experiencing spontaneous labor (Glantz, 2005; Smith et al., 1984). Some research has calculated higher than average length of stay in maternity units among induced women (Vrouenraets et al., 2005; Glantz, 2005), as well as higher delivery costs (Maslow et al., 2000). Other studies found no adverse impact associated with the induction of labor. Smith et al. (1984) found that when careful patient selection is made by an experienced clinician, planned delivery does not jeopardize the outcomes of either the mother or fetus compared to spontaneous labor. This result was similar to that of Cole et al. (1975) who found no evidence that elective induction of labor increased fetal or maternal morbidity.
The purpose of this study was to assess maternal and neonatal outcomes associated with the induction of labor among low risk women who lacked identifiable indications for induction at term.
Data Sources: To examine induction trends, Utah birth certificate records from 1992 through 2005 were used. Induction of labor was measured by birth certificate item ‘induction’ and identifies all deliveries where induction of labor was attempted, regardless of whether the induction was successful. On the birth certificate record, induction is defined as the initiation of uterine contractions before the spontaneous onset of labor by medical and/or surgical means for the purpose of delivery. Excluded from the study were records of births where stimulation or augmentation of a previously established labor was indicated. The birth certificate does not distinguish between elective and indicated inductions, but it does contain information on most of the medical indications related to induction. Induction rates per 100 live births in Utah were compared with overall U.S. rates.
Maternal and neonatal outcomes related to the induction of labor without an identified indication were assessed using only 2005 birth certificate data.
Study Selection Criteria: The study included women with singleton births clinically estimated to be between 38-40 completed weeks’ gestation. The clinical estimate of gestational age on the birth record is defined as the age in total weeks completed from the last menstrual period date to the date of delivery. Gestational age parameters 38-40 weeks were selected based on a review of the parameters used in recent induction research to identify a low-risk group. The study was also limited to women who gave birth in a hospital. In order to define infants in vertex presentation, women with breech/malpresentations were excluded. To further limit the study to low-risk women, records with one or more listed medical risk factors for pregnancy were excluded. Many of the risk factors in the birth certificate records are recognized by ACOG as indications for induction, and include: pregnancy induced hypertension, premature rupture of membrane, Rh sensitization, acute or chronic lung disease, chronic hypertension, polyhydramnios/oligohydramnios, pre-existing diabetes, gestational diabetes, renal disease, and eclampsia. Examination of previous pregnancy history resulted in the removal of women with previous preterm, macrosomic, or SGA infants, since history of such conditions may point toward an increased risk for similar complications. The remaining group was further reduced to exclude those with certain complications of pregnancy. The complications excluded for were: placenta previa, abruptio placenta, umbilical cord prolapse, incompetent cervix, uterine bleeding, cephalopelvic disproportion, and genital herpes. Several of these listed complications are defined by ACOG as contraindications for induction, and, as such, disqualify the subjects from being considered ‘low risk’. Women diagnosed as febrile were excluded from the study on the basis of the suggestion that the condition could be considered a proxy for “chorioamnionitis”, which is also a recommended indication for induction by ACOG (MacDorman et al., 2002). The final step in defining the study population was to remove all birth records where the mother was indicated to have had any previous cesarean delivery. This final study population was divided into two groups: those induced and those non-induced, in order to compare maternal and neonatal outcomes. The flowchart of selection of study participants is presented in Figure 1.
Study Participants: During 2005, there were 51,517 resident births in Utah. Of these, only 38,153 women who delivered at a hospital with a single infant in vertex presentation in the gestational age range of 38-40 weeks were initially included for this study. The application of exclusion criteria resulted in a total of 14,809 women as the final study population. Among these, 5,945 women had labor induced and were compared with 8,864 non-induced women.
Outcomes: Maternal outcome was measured in terms of incidence of cesarean and instrumental delivery. Instrumental delivery was defined as any use of either forceps or vacuum during a vaginal delivery. Neonatal outcomes of interest included birth weight, Apgar scores at 1 and 5 minutes, the presence of moderate/heavy meconium, birth injury, fetal distress, hyaline membrane disease/ RDS, or assisted ventilation.
Statistical Analysis: The analyses performed included descriptive summary statistics, chi square, t-test, and regression. Multivariate logistic regression mod-els were developed to estimate the effect of induction on the risk of cesarean and instrumental delivery while adjusting for potential confounders. Adjusted odds ratios (OR) with 95% confidence interval were generated from regression models. All analyses were performed using SAS version 9.1 (SAS Institute Inc., Cary, NC, USA).
Trend Data: The overall induction (indicated and non-indicated) rate in Utah increased from 16.4% in 1992 to 35.3% in 2005. This represents a 115% increase. Utah’s rate is significantly higher than the national average (33.6% vs. 21.2%, 2004 data). The trends in induction rates in Utah and the U.S. are presented in Figure 2.
Assessment of Outcomes
Characteristics of Participants: Shown in Table 1 are selected maternal characteristics of women who underwent induction of labor compared with those whose labor was not induced. Women with induced labor were slightly older and had more education compared to the non-induced group. A difference was also noted in the proportion of nulliparous women, which was lower in the induction group compared with the non-induction group (30.3% vs. 42.2%). The induction group had a higher proportion of married women compared to the non-induced group (87.4% vs. 82.1%).
Induction of Labor and Maternal Outcomes: The primary maternal outcomes measured in this study were the risk of cesarean section or instrumental delivery associated with labor induction. A comparison of induced and non-induced women delivering infants by various modes is presented in Table 2.
This study revealed slight differences in cesarean rates between the induced and non-induced group. The primary c-section rate for the induction group was significantly lower compared to the non-induced group (4.1% vs. 5.8%, p< .001). Overall, the use of instruments associated with vaginal delivery was similar in both groups (10.4% vs. 10.0%). However, when analyzed by parity, nulliparous women in the induction group had a significantly higher instrumental delivery rate compared to the nulliparous in the non-induced group (22.8% vs. 17.7%, p<.001; see Table 3).
Since instrumental delivery among nulliparous women was correlated with birth weight and maternal age, as well as induction, we used a logistic regression model to adjust for these potentially confounding characteristics. Instrumental delivery was designated as the dependent variable in the logistic model, with group (induction vs. non-induction) as an independent variable, and birth weight and maternal age as covariates. The odds ratio for instrumental delivery adjusted for these confounding factors is shown in Table 4. The nulliparous women in the induced group were 1.36 times more likely to experience instrumental delivery compared to the nulliparous women in the non-induced group, regardless of maternal age or newborn’s birth weight.
Neonatal Characteristics: Neonatal characteristics at birth are presented in Table 5. The average neonatal weight at birth in the labor induction group was 3,416 grams compared with 3,365 grams in the non-induced group (p<.05). In the induced group, a higher proportion of newborns were macrosomic (≥ 4,000 g) compared to newborns in the non-induced group (6.5% vs. 5.8%, p <.05). The prevalence of low birth weight (<2,500 g) neonates were slightly lower in the induced group compared to the non-induced group (0.6% vs. 1.0%, p<.05). There were no significant differences in Apgar scores of less than 7 at either 1 or 5 minutes between the induced and non-induced groups.
Neonatal Outcomes: Neonatal outcomes associated with induction are provided in Table 6. The proportion of newborns with birth injury did not differ significantly between the induced and non-induced group (1.1% vs. 1.3%). This study observed that meconium staining occurred more frequently among the non-induced group compared to the induced group (7.1% vs. 3.6%, p<.001). No significant difference in the proportion of newborns with hyaline membrane disease/RDS, assisted ventilation, or fetal distress was observed.
Time and Day of Delivery: In 2005, the majority of induced deliveries (80%) occurred between 8 AM and 8 PM, compared to 60% among the non-induced (see Table 7). Women who had labor induced were also more likely to deliver on weekdays (Monday – Friday) compared to the weekend, with a preponderance Tuesday – Thursday (see Figure 3).
Induction rates are increasing rapidly both locally and nationally. Increases were seen among women with documented medical indications as well as among women with elective inductions (Yeast et al., 1999). Explanation of the dramatic increase in the incidence of labor induction is certainly complex and may be comprised of numerous contributing factors (Rayburn et al., 2002; Zhang et al., 2002). A suggested primary reason for the rising usage of induction centers on the ability it provides to plan the timing of birth for the physician, patient, and family. Other explanations include the increasing availability of effective cervical ripeners and medical liability concerns associated with continued expectant management, particularly post-term (Rayburn et al., 2002). In addition, the ability to more accurately determine the gestational age of the neonate, and more sophisticated techniques of antepartum fetal surveillance may also contribute to the rising induction rate (Yeast et al., 1999).
In assessing maternal outcomes using 2005 birth certificate data, this study found that the cesarean delivery rate was lower among the induced group compared to the non-induced group. This finding is consistent with the findings of Cole et al. (1975). However, other previous studies have documented an increased rate of cesarean delivery with elective induction, particularly among the nulliparous (Macer et al., 1992; Smith et al., 1984; Yudkin et al., 1979).
In this study instrumental delivery rates did not differ between the induced and non-induced groups overall. This parallels the finding of Cole et al. (1975), where forceps use was similar in both groups of women, those induced and those experiencing spontaneous labor. Their study also found that the use of epidurals is more commonly associated with elective induction than with women experiencing spontaneous labor. Therefore, it has been hypothesized that it may be epidural analgesia rather than induction that is the causal factor explaining the higher incidence of instrumental delivery among induced women. Wigton et al. (1994) also noted that patients receiving epidurals were more likely to require instrumental delivery. When they controlled for the influence of epidurals, in their analysis, they found no difference in instrumental delivery rates between induced and non-induced groups. This study was unable to control for epidural use because of the unavailability of data. While no differences in instrumental delivery rates were observed in this study between the induced and non-induced groups, when parity was introduced, an increased risk of instrumental delivery was observed among nulliparous women (OR = 1.36, 95% CI 1.18 – 1.58). This is of concern since research has documented a link between instrumental delivery and maternal morbidity such as soft tissue injury/discomfort, maternal hematoma, and pelvic floor injury. Vacuum extraction may also “result in significant fetal injury if misused;”, problems such as cephalohematoma, subgaleal hematoma, intracranial hemorrhage, hyperbilirubinemia, and retinal hemorrhage may result (ACOG, 2000).
Comparison of neonatal outcomes showed that women with induced labor without an identified indication had, on the average, infants with higher birth weights. These findings are in accordance with those of Macer et al. (1992). In this study no association was observed between induction of labor and birth injury. However, previous studies, particularly research done by Dublin et al. (2000), found birth injuries were more common among infants born to women whose labors were induced. The greater prevalence of meconium staining among the non- induced group in this study population, was consistent with the findings of previous studies (Dublin et al., 2000; Smith et al., 1984), who found that meconium was present much less frequently in the electively induced group. The findings of no association between induction and low Apgar scores (<7) were also consistent with previous studies (Dublin et al., 2000; Macer et al., 1992; Smith et al., 1984). Overall, in this study, the neonatal outcomes between the induced and non-induced groups were similar.
This study found that the majority of induced women were delivered on weekdays in the afternoon or early evening hours. By contrast, the deliveries of non-induced or spontaneously laboring women were distributed evenly over the 24-hour period. These findings parallel those reported in other studies (Macer et al., 1992; Smith et al., 1984). In this study women who had labor induced were found to be more likely to deliver on weekdays. This may support the hypothesis that a primary attraction of induction is the opportunity it provides to choose a convenient delivery time.
Several limitations may be noted in this study. The birth certificate contains information on maternal medical risk factors, labor complications, and induction of labor, however, it does not distinguish between elective induction and medically indicated induction. This study assumed that women without medical risk factors and certain selected labor complications may be defined as low-risk, healthy women undergoing induction. It is possible that women may have had other mitigating factors not reported on the birth certificates, such as joint pain, back pain, edema, indigestion, distance from hospital, or psychosocial issues that influenced the physician’s decision for induction. Such information may be present in medical charts or in other medical records.
Another limitation is that some information of potential interest in assessing induction of labor is not included in birth certificate data. This information includes items such as Bishop’s score for cervical ripening, the different methods of induction, use of epidural analgesia, and length of labor. It is possible that the associations observed in this study between the induction of labor and various maternal and neonatal outcomes may be linked with particular methods of induction only, as mentioned by Dublin et al. (2000). There were also no intrapartum or postpartum complications recorded on the birth certificate, such as hemorrhage, laceration, etc. Incomplete information regarding medical history remains an important limitation of this study and warrants caution in the interpretation of these findings. It is possible that there were other differences between women with induced labor and those with non-induced labor that were unable to be measured in this study.
In conclusion, overall maternal and neonatal outcomes were not adversely affected by induction among low-risk women who lacked an identified indication. However, induction was associated with increased risk for instrumental delivery among nulliparous women in this study. Therefore, it is recommended that all women receive full disclosure of the benefits and risks associated with induction before undergoing this obstetric procedure. Further studies need to be undertaken as Utah’s induction rate is significantly higher than the national rate.
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We thank Brenda Ralls PhD, Sharon Talboys, MPH, Karen Zinner, MPH, and Tara Johnson, MS for their valuable comments about data analysis and interpretations.