Inducing labor at 40 weeks of gestation rather than waiting a week or two lowers the risk for perinatal death in first-time mothers aged 35 years or older, according to findings published November 14 in PLOS Medicine.
“[I]nduction of labour at 40 weeks of gestation was associated with a 66% lower risk of perinatal death (0.08% versus 0.26%) than expectant management, without increasing the risk of emergency caesarean section,” the researchers write.
In the United Kingdom, labor induction is not typically done until 41 or 42 weeks of gestation, but some evidence suggests that induction at 40 weeks may be safe for the mother. An investigation demonstrating that inducing labor at 39 weeks does not elevate risks to the mother did not assess risk for perinatal death.
Hannah E. Knight, PhD, from the London School of Hygiene & Tropical Medicine, United Kingdom, and colleagues used English Hospital Episode Statistics data from April 2009 to March 2014 to examine the association between induction of labor at 39 weeks or later and the risk for perinatal mortality for first-time births among women aged 35 years or older. They compared results for women who were induced at 39, 40, or 41 weeks with results for those who continued their pregnancy to spontaneous labor, induction of labor, or cesarean delivery at a later gestation.
The researchers found that labor was induced in 25,583 (33.1%) of 77,327 nulliparous women aged 35 to 50 years with single births. Compared with expectant management, labor induction at 40 weeks was associated with lower risk for in-hospital perinatal death (0.08% vs 0.26%; adjusted risk ratio [adjRR], 0.33; 95% confidence interval [CI], 0.13 – 0.80; P = .015) and meconium aspiration syndrome (0.44% vs 0.86%; adjRR, 0.52; 95% CI, 0.35 – 0.78; P = .002), but with slightly increased risk for instrumental vaginal delivery (adjRR, 1.06; 95% CI, 1.01 – 1.11; P = .020) and emergency cesarean delivery (adjRR, 1.05; 95% CI, 1.01 – 1.09; P = .019).
Induction at 40 weeks was associated with a small increase in risk for instrumental vaginal delivery (adjRR, 1.06; 95% CI, 1.01 – 1.11) and emergency cesarean delivery (adjRR, 1.05; 95% CI, 1.01 – 1.09) and at 41 weeks with a slightly lower risk for emergency cesarean delivery (adjRR, 0.94; 95% CI, 0.90 – 0.97) compared with expectant management. Rates of severe perineal tears were similar for different delivery times.
The findings indicate that 562 (95% CI, 366 – 1210) labor inductions at 40 weeks would be necessary to prevent one perinatal death.
The researchers conclude that for women aged 35 years or older, “Induction of labour at term is associated with a lower rate of perinatal mortality and morbidity. Hence, bringing forward the routine offer of induction of labour from the current recommendation of 41–42 weeks to 40 weeks of gestation in this group may reduce overall rates of perinatal death.” At 41 and 42 weeks, the risk for stillbirth is 2 to 3 per 1000.
“This study represents the strongest evidence yet that moving the offer of induction forward to 40 weeks might reduce the risk of stillbirth in this specific age group, which we know face a greater risk of stillbirth and neonatal death,” said Dr Knight in a London School of Hygiene & Tropical Medicine news release. Further studies are needed to assess consequences of encouraging earlier induction of labor, such as effect on costs and patient acceptability.
Limitations of the study include use of observational data, assessing gestational age by weeks and not days, possible under-reporting of labor induction and perinatal death, and unaccounted-for confounders.
“The RCOG [Royal College of Obstetricians and Gynaecologists] welcomes any new research which may help to reduce stillbirth and neonatal death rates, however, as the authors acknowledge, the implications of such a change in policy would be enormous for both the health service and women themselves so further research to determine the impact of such a change in practice is needed,” Professor Lesley Regan, RCOG president, said in an RCOG news release.
“While induction is safe and studies have shown no short-term adverse impact on mother or baby, induction of labour represents an intervention, is associated with costs to the service, and can be a more prolonged process than spontaneous labour. These findings should help women over the age of 35 make an informed choice with regards to induction of labour and are likely to influence the production of future guidelines.”
Dr Smith receives research support from GE, Roche, and GSK and holds a patent for use of a GSK compound to prevent preterm birth. The remaining investigators have disclosed no relevant financial relationships.
PLOS Med. Published online November 14, 2017. Full text
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