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Elective Induction at Term Reduces Perinatal Mortality Without Increasing Operative Delivery? Looking Behind the Curtain

A recent study of elective induction at term purports to show that it would reduce perinatal mortality without affecting spontaneous birth rates, although it would increase admission to a special neonatal care unit if done before 41 weeks. The study, conducted in Scotland, analyzed outcomes of 1,271,549 women carrying a singleton, head-down baby of 37 to 40 weeks gestation who gave birth between 1981 and 2007. (Forty-one weeks was considered postterm.) Women with prior cesarean, breech baby, or placenta previa were excluded. Elective induction was defined as induction with no medical indications (hypertensive or kidney disorders, thromboembolic disease, diabetes, liver disorders, pre-existing medical disorder, antenatal investigation of abnormality, suspected fetal abnormality, fetal compromise, or previous stillbirth or neonatal death), and 176,136 women met these criteria. Perinatal mortality was defined as stillbirth or death within the first month, excluding deaths associated with congenital anomalies. Outcomes were adjusted for maternal age, parity (no prior births vs. one or more prior births), time period, and birth weight.

Investigators reported outcomes by week in two ways: women electively induced compared with women not electively induced who delivered after that week and women electively induced compared with women not electively induced who delivered in or after that week. I will report outcomes according to the second method because it is less biased.

Perinatal mortality rates declined from 2.4 per 1000 at 37 weeks to 1.6 per 1000 at 41 weeks in the “not electively induced” population and varied from 0.9 to 0.6 per 1000 in the electively induced population, showing no trend, which meant that the excess

Drewesque, via Flickr, Creative Commons Attribution

perinatal mortality rate fell from 2.3 per 1000 more deaths at 37 weeks in the “not electively induced” population to 0.9 more at 41 weeks. That would seem to clinch the argument for elective term induction were it not for one fatal flaw: investigators did not compare similar populations. They isolated a low-risk—I may even say ultra-low-risk—group of women and compared them with everyone else, including women with the high-risk conditions listed above! Finding lower perinatal mortality rates should not be surprising. It would have been extraordinary if they had not.

Even with that advantage, more babies were admitted to special or intensive care nurseries after elective induction at every week through 40 weeks, which contradicts the current belief that elective delivery at 39 weeks poses no excess risk. Excesses declined from 94 more babies per 1000 with elective induction at 37 weeks to 10 more babies per 1000 at 40 weeks. (At 41 weeks, 3 more babies per 1000 were admitted to special or intensive care in the “not electively induced” population.)

What about finding similar spontaneous vaginal birth rates? Spontaneous birth rates were, indeed, similar between groups, but more women delivered via cesarean surgery in the electively induced group. Depending on the week, 0.3 to 1.5 more women per 100 electively induced had cesareans. Spontaneous birth rates were similar because the cesarean excess was offset by an excess of instrumental vaginal deliveries at each week in the “no elective induction” group. An excess of instrumental deliveries is concerning primarily because of the increased likelihood of anal sphincter injury; however, an excess in cesarean deliveries is far more serious, carrying as it does increased likelihood of severe maternal and perinatal morbidity and mortality in both current and future pregnancies.

Rob, Joyce, Alex & Nova's photostream, via Flickr, Creative Commons Attribution

Rob, Joyce, Alex & Nova's photostream, via Flickr, Creative Commons Attribution

Furthermore, the investigators chose not to report cesarean rates according to parity. Women with a prior vaginal birth or births will be little affected by induction, but first-time mothers are a different story. Studies (see references below) comparing term elective induction with spontaneous onset report that elective induction roughly doubles the chance of cesarean with excesses ranging from 3 to 31 more women per 100 having labor end in cesarean. Three studies (Hannah et al. 1996, Kassab et al, 2011; Pavicic et al. 2009.) specifically evaluating elective induction at 41 weeks compared with expectant management for at least one more week in low-risk first-time mothers report a remarkably similar excess: 8 to 9 more cesareans per 100 women induced electively. In first-time mothers, then, the excess cesarean surgery rate was almost certainly much greater than the excess rate in the Scottish population overall.

So there you have it. Does elective induction at term save babies? We don’t know because the investigators compared apples to oranges. It certainly increases likelihood of admittance to special or intensive neonatal care through 40 weeks, an excess all the more ominous because comparison women were not all low risk. It’s also a safe bet that it substantially increases cesarean surgery rates in first-time mothers going by what other studies have found. And, again, the excess would likely have been greater even in the population overall had investigators compared low-risk women to low-risk women. Lesson learned: if you don’t look at what’s behind the curtain, you may get very misleading ideas of what is really going on.

Boulvain, M., Marcoux, S., Bureau, M., Fortier, M., & Fraser, W. (2001). Risks of induction of labour in uncomplicated term pregnancies Paediatr Perinat Epidemiol, 15(2), 131-138.

Cammu, H., Martens, G., Ruyssinck, G., & Amy, J. J. (2002). Outcome after elective labor induction in nulliparous women: A matched cohort study. Am J Obstet Gynecol, 186(2), 240-244.

Dublin, S., Lydon-Rochelle, M., Kaplan, R. C., Watts, D. H., & Critchlow, C. W. (2000). Maternal and neonatal outcomes after induction of labor without an identified indication. Am J Obstet Gynecol, 183(4), 986-994.

Ehrenthal, D. B., Jiang, X., & Strobino, D. M. (2010). Labor induction and the risk of a cesarean delivery among nulliparous women at term. Obstet Gynecol, 116(1), 35-42.

Glantz, J. C. (2005). Elective induction vs. Spontaneous labor associations and outcomes. J Reprod Med, 50(4), 235-240.

Le Ray, C., Carayol, M., Breart, G., & Goffinet, F. (2007). Elective induction of labor: Failure to follow guidelines and risk of cesarean delivery. Acta Obstet Gynecol Scand, 86(6), 657-665.

Luthy, D. A., Malmgren, J. A., & Zingheim, R. W. (2004). Cesarean delivery after elective induction in nulliparous women: The physician effect. Am J Obstet Gynecol, 191(5), 1511-1515.

Macer, J. A., Macer, C. L., & Chan, L. S. (1992). Elective induction versus spontaneous labor: A retrospective study of complications and outcome. Am J Obstet Gynecol, 166(6 Pt 1), 1690-1696; discussion 1696-1697.

Maslow, A. S., & Sweeny, A. L. (2000). Elective induction of labor as a risk factor for cesarean delivery among low-risk women at term. Obstet Gynecol, 95(6 Pt 1), 917-922.

Prysak, M., & Castronova, F. C. (1998). Elective induction versus spontaneous labor: A case-control analysis of safety and efficacy. Obstet Gynecol, 92(1), 47-52.

Seyb, S. T., Berka, R. J., Socol, M. L., & Dooley, S. L. (1999). Risk of cesarean delivery with elective induction of labor at term in nulliparous women. Obstet Gynecol, 94(4), 600-607.

Vahratian, A., Zhang, J., Troendle, J. F., Sciscione, A. C., & Hoffman, M. K. (2005). Labor progression and risk of cesarean delivery in electively induced nulliparas. Obstet Gynecol, 105(4), 698-704.

van Gemund, N., Hardeman, A., Scherjon, S. A., & Kanhai, H. H. (2003). Intervention rates after elective induction of labor compared to labor with a spontaneous onset. A matched cohort study. Gynecol Obstet Invest, 56(3), 133-138.

Vardo, J. H., Thornburg, L. L., & Glantz, J. C. (2011). Maternal and neonatal morbidity among nulliparous women undergoing elective induction of labor. J Reprod Med, 56(1-2), 25-30.

Vrouenraets, F. P., Roumen, F. J., Dehing, C. J., van den Akker, E. S., Aarts, M. J., & Scheve, E. J. (2005). Bishop score and risk of cesarean delivery after induction of labor in nulliparous women. Obstet Gynecol, 105(4), 690-697.

Yeast, J. D., Jones, A., & Poskin, M. (1999). Induction of labor and the relationship to cesarean delivery: A review of 7001 consecutive inductions Am J Obstet Gynecol, 180(3 Pt 1), 628-633.

Cesarean Birth, Do No Harm, Evidence Based Medicine, Guest Posts, Healthy Birth Practices, Healthy Care Practices, Maternity Care, Medical Interventions, New Research, Research, Uncategorized , , , , , , , , , ,

  1. avatar
    Denise Hynd
    May 29th, 2012 at 21:10 | #1

    Another thorough evaluation thank you

  2. May 30th, 2012 at 07:18 | #2

    Thank You, Henci! :>)
    Amy

  3. May 30th, 2012 at 11:13 | #3

    You’re welcome!

  4. May 30th, 2012 at 15:40 | #4

    Thank you Henci for this post. I appreciate that you are willing to share information and insight with our community so freely. Thanks!

  5. May 31st, 2012 at 09:22 | #5

    Wow thorough review…great info, thanks Henci!

  6. May 31st, 2012 at 11:46 | #6

    Thank you, Henci! This is the kind of solid information we need.

  7. May 31st, 2012 at 15:17 | #7

    Your kind words are much appreciated. I feel so lucky to be able to do something that others find helpful and that is my idea of a good time. How many others can say that about their work?

  8. June 1st, 2012 at 18:21 | #8

    Nicely done! And a great example of why you can’t just say, “this is what the study found.” You have to actually get in there and evaluate the quality of the evidence.

  9. June 1st, 2012 at 21:47 | #9

    @Rebecca Dekker
    Thanks! I was just reading your blog post on IVs yesterday. Amy Romano had posted a link to it from our *Optimal Care in Childbirth* website, and I can return the compliment. I printed it out and filed it for future reference.

  10. June 2nd, 2012 at 01:31 | #10

    I thought this was an interesting article because they showed that inductions increase NICU visits but did not increase mortality(or decreased mortality). This was a red flag to me that something was wrong with this study. This just does not make sense. What I would like to know is if we might find a difference in mortality rates between midwives and ob/gyn’s, and if the mortality rate would in fact decrease if midwives are being used. What I think is going on is that ob’s don’t know how to safely deliver babies using normal physiological principles. So, if you are choosing ob care, it may be safer for you to deliver by induction simply because that is what they know and are good at. However, if you want to bypass the induction it may be safer to go with a midwife because they support normal processes more skillfully. That’s just my thought…I’d love to see this study redone to look at those variables.

  11. June 2nd, 2012 at 09:36 | #11

    In most European countries, midwives are the bedside attendants, so I expect this was the case in Scotland. In a case such as breech, I would agree with you that a cesarean may be safer because few obs know how to assist safely at a breech vaginal birth, but that wouldn’t apply to induction. In fact, the opposite is likely to be true. A patient care provider who has spontaneous vaginal birth as the goal whenever it is safely possible and who is conscious of the potential harms of induction and uses strategies to minimize them is more likely to achieve safe vaginal birth of a healthy baby than one who is none of the above. Also, such a practitioner could be an ob, and a midwife may not fit this description. It isn’t about the profession but the practice philosophy and style.

  1. May 31st, 2012 at 14:29 | #1