Professor, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora
Dr. Hobbins reports no financial relationships relevant to this field of study.
SYNOPSIS: The authors of an abstract presented at the annual meeting of the Society for Maternal-Fetal Medicine suggested that inducing low-risk obstetrical patients at 39 weeks is associated with significantly diminished rates of cesarean delivery and the need for neonatal respiratory support.
SOURCE: Grobman W. A randomized trial of elective induction of labor at 39 weeks compared with expectant management of low risk nulliparous women. Abstract from the Society for Maternal-Fetal Medicine. Am J Obstet Gynecol 2018;218(Suppl):S601.
Usually, clinical alerts in obstetrics and gynecology are generated from published reports that have been vetted through rigorous peer review, but this month I wanted to be out ahead of a media airing of an abstract that was published in the proceedings of the 2018 annual meeting of the Society for Maternal-Fetal Medicine in Dallas. The research was presented during the opening plenary session as a late-breaking paper that could affect the way obstetrics is practiced. William Grobman relayed the results of a randomized, clinical trial (RCT), supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, to determine if benefit could be accrued from empiric elective inductions at 39 weeks of gestation, rather than awaiting spontaneous delivery.
Low-risk nulliparous women with ultrasound-documented gestational ages were randomized at 38 weeks to have either an induction of labor (IOL) at 39/0 to 39/4 weeks or to forgo elective delivery until 40/5 weeks, but not past 42/2 weeks. The primary outcome studied was the incidence of adverse outcomes, and the secondary outcome variable was the cesarean delivery rate (CR). All patients had cervical Bishop scores at the time of enrollment.
Forty-one hospitals participated in the study. After exclusions were applied, 3,062 patients were allocated to the IOL group and 3,044 to the electively managed (EM) control group. Not surprisingly, the IOL group, on average, delivered earlier than the EM group, but by only four days (39/3 vs. 40/0 weeks; P < 0.001). There was a trend toward a lower rate of composite adverse neonatal outcomes in the IOL group (4.4% vs. 5.4%; 95% confidence interval [CI], 0.64-1.01). Although there was a significantly lower need for neonatal respiratory support in the IOL group (3.0% vs. 4.2%; 95% CI, 0.55-0.93), all other neonatal variables were similar between groups. On the maternal side, the CR was significantly lower in the IOL group (18.6% vs. 22.2%; 95% CI, 0.76-0.93), as well as the risk of preeclampsia and/or hypertension alone (9.1% vs. 14.1%; 95% CI, 0.56-0.74), with no difference in postpartum hemorrhage (4.6% vs. 4.5%).
This study could stand traditional obstetrical management on its head. The IOL had steadily crept up to 23.7% in 2011, but it leveled off to 23.3% the next year,1 likely because of awareness of the unfortunate fallout of increased neonatal morbidity associated with unexpected prematurity in early-term deliveries. In 2009 and again in 2013, the American College of Obstetrics and Gynecology (ACOG) suggested that elective delivery by any route be delayed until 39 weeks.2 Most published randomized studies comparing IOL with EM have dealt with patients who were post-term, but there were two non-randomized studies that alerted clinicians to a possible benefit of induction in low-risk patients at term.3,4 In 2016, during a debate at the annual ACOG meeting regarding the efficacy of IOL vs. EM in term patients (39 to 40 weeks), both debaters, including the one assigned to be pro-EM (Dr. Charles Lockwood), concluded that the existing data pointed toward induction.5 They and other authors have called for evidence via an RCT at 39 weeks. Well, here it is, and it deals with low-risk women, 63% of whom had unfavorable cervices by Bishop score — just the ones with whom we have been least likely to meddle. And, lo and behold, induction seems to improve outcomes, rather than creating morbidity.
You may have noticed from previous alerts that on occasion I have taken a nihilistic approach to various obstetrical management options, simply because, at times, Mother Nature appears to be smarter than we are. However, that same Mother Nature, who was responsible for the remarkable human brain, heart, and placenta, also brought us cancer. So maybe her timing of spontaneous labor in uncomplicated pregnancies is a bit off — certainly if the goal is to avoid perinatal complications. Another possibility is that our basic calculation for an estimated date of confinement (EDC) is flawed.
The EDC story started in 1744, with the Dutch professor Herman Boerhaave, who determined in 100 pregnant women that the average time of delivery occurred at 40 menstrual weeks. Later, this was highlighted by a German professor, Carl Naegele, in 1812, but it was never clear whether the starting point was the first day of the last menstrual period (LMP) or the last day. Naegele’s rule later was adjusted so that clinicians would always use the first day of LMP, with 280 days being assigned as term.
The obvious problem with using LMP as a starting point are the errors in calculation caused by early or late ovulation. To weed out these confounders, ultrasound has been used to determine more precisely when the first day of the LMP “should have been.”
Below is current information on pregnancy length based on either ultrasound documentation in the first trimester or precisely documented ovulations.
- The average time of delivery in uncomplicated first-time pregnancy was 40/5 weeks (285 days) and in multiparous patients it was 40/3 weeks (283 days).6,7
- By applying ultrasound dating, the rate of post-term pregnancies (≥ 42 weeks) was diminished from 10.3% in those with clinically “certain” LMP to 2.7%.8 If the ultrasound was done between 11 and 14 weeks, 68% of patients delivered within 11 days of their EDCs.9
- The fewest neonatal complications occurred between 39/0 weeks and 41/6 weeks.10
So, the age-old “wheel of fortune” carried in the coat pockets of providers is only a couple of days off in predicting EDC, and this information should not affect the meaning of the above featured study, done by some of the most respected investigators in the field.
A strong word of caution. Before we automatically endorse the concept of inducing every pregnant patient at 39 weeks, this information needs to be peer-reviewed formally, digested, and debated. Another RCT with similar results also would help. Although now the data certainly appear very compelling, individual circumstances vary and a preference for non-intervention from an informed patient always should be respected.
- Centers for Disease Control and Prevention. Recent declines in induction of labor by gestational age. June 18, 2014. Available at: https://www.cdc.gov/nchs/products/databriefs/db155.htm. Accessed Feb. 23, 2018.
- American College of Obstetricians and Gynecologists. ACOG committee opinion no. 561: Nonmedically indicated early-term deliveries. Obstet Gynecol 2013;121:911-915.
- Caughey AB, Sundaram V, Kaimal AJ, et al. Systematic review: Elective induction of labor versus expectant management of pregnancy. Ann Intern Med 2009;15:252-263.
- Gibson KS, Waters TP, Bailet JL. Maternal and neonatal outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014;211:249.e1-6.
- American College of Obstetrics and Gynecology. 2016 Annual Meeting.
- Smith GC. Use of time to event analysis to estimate the normal duration of human pregnancy. Hum Reprod 2001;16:1497-1500.
- Jukic AM, Baird DD, Weinberg CR, et al. Length of human pregnancy and contributions to its natural variation. Hum Reprod 2013;28:2848-2855.
- Taipale P, Hiilesmaa V. Predicting delivery date by ultrasound and last menstrual period in early gestation. Obstet Gynecol 2001;97:189-194.
- Khambalia AZ, Roberts CL, Nguyen M, et al. Predicting date of birth and examining the best time to date pregnancy. Int J Gynaecol Obstet 2013;123:105-109.
- Spong CY. Defining “term” pregnancy: Recommendations from the Defining “Term” Pregnancy Workgroup. JAMA 2013;309: 2445-2446.