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The impact of induction of labor at 39 weeks in low-risk women on the incidence of stillbirth

Published:September 20, 2019DOI:https://doi.org/10.1016/j.ajog.2019.09.032

      Objective

      A large randomized trial showed that induction of labor between 39 0/7 weeks and 39 4/7 weeks in nulliparous low-risk women without medical indications for induction was associated with a trend for less perinatal morbidity and mortality, significantly fewer cesarean deliveries, and fewer hypertensive disorders compared to expectant management.
      • Grobman W.A.
      • Rice M.M.
      • Reddy U.M.
      • et al.
      Labor induction versus expectant management in low-risk nulliparous woman.
      The objective of this study was to evaluate the impact of induction of labor between 39 0/7 weeks and 39 4/7 weeks on the incidence of stillbirth in low-risk women in the United States.

      Study Design

      We used US vital statistics data from Live Birth and Fetal Death certificates, of births between January 1, 2014, and December 31, 2016. We included singleton deliveries at ≥39 weeks without preexisting maternal risk factors. We excluded women with pregestational diabetes, chronic hypertension, scheduled cesarean delivery, unknown delivery method, or unknown gestational age.
      The primary outcome was the stillbirth rate at ≥39 weeks in singleton pregnancies in low-risk women. This represents the number of potentially preventable stillbirths with a policy of induction at 39 weeks. As the ARRIVE trial
      • Grobman W.A.
      • Rice M.M.
      • Reddy U.M.
      • et al.
      Labor induction versus expectant management in low-risk nulliparous woman.
      induced labor in women in the intervention group between 39 0/7 and 39 4/7 weeks, not all stillbirths occurring in the 39th week may be prevented by induction in the 39th week, because some stillbirths could occur in the 39th week in pregnancies that have not yet undergone delivery. Thus, we conservatively estimated that induction of low-risk pregnancies at 39 weeks would prevent about half of the stillbirths in the 39th week. We also calculated the number of inductions needed to prevent 1 stillbirth and the prospective stillbirth rate at ≥39 weeks.
      The study was deemed to be exempt from institutional review board approval. Analysis was performed using STATA 15 (StataCorp, College Station, TX).

      Results

      Results are shown in the Figure. A total of 12,098,773 births, including 155,753 stillbirths, occurred in the United States during our study period. Among 3874 stillbirths at ≥39 weeks, 3584 occurred in low-risk women (stillbirth rate of 0.60 per 1000 births). This represents on average of 1194 stillbirths per year at ≥39 weeks. Assuming conservatively that only half of the stillbirths occurring during the 39th week (n = 1869) in our study period would be prevented by a policy of induction at about the 39th week, the total number of preventable stillbirths during the 3-year study period was 2650 (883 stillbirths per year). The number of inductions at ≥39 weeks in low-risk singleton gestations needed to prevent one stillbirth is 1675.
      Figure thumbnail gr1
      FigureFlow diagram of number of US total births and stillbirths from 2014 to 2016, without exclusion criteria, at 22–36 weeks, 37–38 weeks, and ≥39 weeks with and without pre-existing risk factors and prospective stillbirth rates at ≥ 39 weeks
      Po’. Impact of induction of labor at 39 weeks in low-risk women on the incidence of stillbirth. Am J Obstet Gynecol 2020.

      Conclusion

      The stillbirth rate in low-risk women at ≥39 weeks is 0.60 per 1000 births. Induction of labor in low-risk women between 39 0/7 weeks and 39 4/7 weeks would potentially prevent 833 stillbirths per year in the United States alone. The number of inductions needed to prevent 1 stillbirth is approximately 1675.
      Compared to expectant management, induction of labor between 39 0/7 weeks and 39 4/7 weeks in low-risk women has been previously associated with a lower risk of cesarean delivery and hypertensive disorders of pregnancy.
      • Grobman W.A.
      • Rice M.M.
      • Reddy U.M.
      • et al.
      Labor induction versus expectant management in low-risk nulliparous woman.
      ,
      • Saccone G.
      • Della Corte L.
      • Maruotti G.M.
      • et al.
      Induction of labor at full-term in pregnant women with uncomplicated singleton pregnancy: a systematic review and meta-analysis of randomized trials.
      On a population level, our study shows in addition that this policy could prevent 883 stillbirths per year in the United States alone. Our data may help low-risk women and their clinicians to make decisions regarding fetal benefits of induction of labor between 39 0/7 weeks and 39 4/7 weeks.

      References

        • Grobman W.A.
        • Rice M.M.
        • Reddy U.M.
        • et al.
        Labor induction versus expectant management in low-risk nulliparous woman.
        N Engl J Med. 2018; 379: 513-523
        • Saccone G.
        • Della Corte L.
        • Maruotti G.M.
        • et al.
        Induction of labor at full-term in pregnant women with uncomplicated singleton pregnancy: a systematic review and meta-analysis of randomized trials.
        Acta Obstet Gynecol Scand. 2019; 98: 958-966

      Linked Article

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        American Journal of Obstetrics & GynecologyVol. 223Issue 1
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          We thank Drs Peleg and Warsof for their letter regarding our manuscript entitled “The impact of induction of labor at 39 weeks in low-risk women on the incidence of stillbirth.” We acknowledge that the background risk of stillbirth increases after 41 weeks gestation. This is applicable to women regardless of their parity.
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      • The impact of induction of labor at 39 weeks on the incidence of stillbirth in low-risk women
        American Journal of Obstetrics & GynecologyVol. 223Issue 1
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          We read with interest the Research Letter by Po’ et al.1 The study described the stillbirth rate per week in the United States from the 39th gestational week onward in low-risk women. The purpose was to determine the impact of induction of labor at 39 weeks on the stillbirth rate in low-risk women. The impetus for the study was based on the results of the ARRIVE trial.2
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