Optimal gestation for elective labour induction

Interestingly, a 2006 paper using a decision analytic model using retrospective data from a single institution finds that after controlling for potential confounders, there was a higher rate of Caesarean delivery risk among women with expectant management beyond 38 weeks (adjusted odds ratio [AOR] 1.80; 95% CI 1.29-2.53), 39 weeks (1.39; 95% CI 1.08-1.80), and 40 weeks (AOR 1.27; 95% CI 1.00-1.62).(Caughey, Nicholson, Cheng, Lyell, & Washington, 2006)

A 2009 systematic review also applying a decision analytic model finds that in each of the models, women who were electively induced had better overall

outcomes among both mothers and neonates as estimated by total quality-adjusted life years as well as by reductions in specific perinatal outcomes such as shoulder dystocia, meconium aspiration syndrome, and preeclampsia. However, the findings of cost-effectiveness at 40 and 39 weeks of gestation were not robust to the ranges of the assumptions made.(Caughey et al., 2009)

Subsequently (2010) a multicentre perinatal database analysis also shows that babies born with elective induction are associated with better neonatal outcomes compared to spontaneous labour but elective induction may be associated with an increased hysterectomy risk.(Bailit et al., 2010)

Another analysis (2011) using data from the Danish Birth registry finds that from gestational week 39 and thereafter, there was no difference with regard to CS rates in labour among nulliparous and parous women when comparing women with induced labour and those women who waited for a later labour, either induced or spontaneous.(Rasmussen & Rasmussen, 2011)

A 2013 Californian birth registry study also indicates with elective induction at 37-40 weeks the odds of caesarean delivery were lower among women with elective induction compared with expectant management across all gestational ages and parity (37 weeks [odds ratio (OR) 0.44, 95% confidence interval (CI) 0.34-0.57], 38 weeks [OR 0.43, 95% CI 0.38-0.50], 39 weeks [OR 0.46, 95% CI 0.41-0.52], 40 weeks [OR 0.57, CI 0.50-0.65] without increased odds of severe lacerations, operative vaginal delivery, perinatal death, neonatal intensive care unit admission, respiratory distress, shoulder dystocia, or macrosomia.(Darney et al., 2013)

A 2013 meta-analysis of labour induction trials in women with intact membranes at term has also reported that “Meta-analysis of 31 trials determined that a policy of induction was associated with a reduction in the risk of caesarean section compared with expectant management (OR 0.83, 95% CI 0.76-0.92)” but cautions that “additional trials are needed”.(Wood, Cooper, & Ross, 2013)

In contrast, analysis using data from a New York State birth-certificate database shows that term labour induction compared with expectant management is associated with increased caesarean risk whether using a week-to-week

comparison group or an expectant group that includes women the same week or beyond that of the index induction: the finding is still robust after adjustment for parity, high-risk factors, and demographic variables.(Glantz, 2010)

There is also indirect evidence from the meta-analysis of secondary data of a few randomised trials that elective labour induction at 37-40 weeks gestation may be associated with a lower Caesarean delivery rate compared to expectant

management but has a higher instrumental vaginal rate(NICE-UK, 2008b) but the finding of reduced Caesarean delivery with labour induction at early term

gestation is not consistently demonstrated(Dunne, Da Silva, Schmidt, & Natale, 2009).

In contrast, from the perspective of neonatal outcome there is increasing evidence that early term (37 to 38 weeks compared to 39 to 41 weeks) delivery is associated with adverse childhood outcome.(Boyle et al., 2012; Dong, Chen, & Yu, 2012)

Race can be a crucial factor to consider in determining the ideal timing for delivery: UK data indicate that black and South Asian women compared to Caucasian women tended to go into spontaneous labour earlier and

correspondingly their babies’ respiratory system appeared to mature at an earlier gestation. In full term South Asian babies, the late gestation rise in antepartum

stillbirth occurs one week earlier than in white Europeans.(Balchin & Steer, 2007;

Balchin, Whittaker, Lamont, & Steer, 2008) Earlier delivery in late term by labour induction may be the better approach in some non-Caucasians to safeguard

neonatal outcome.

The question of an ideal gestation for delivery by elective labour induction in late term as opposed to awaiting spontaneous labour onset can only be settled by large scale powered controlled trials as to its benefit and cost effectiveness. If labour induction becomes indicated by 39 or 40 weeks gestation, the implication for obstetric care is profound as by the end of 38 weeks or 39 weeks, probably up to 80% and 50% of pregnancies at these respective gestations would not have spontaneously laboured yet leaving a majority to need elective labour induction.

4.5.1. Facilitating spontaneous labour and preventing a prolonged pregnancy There is epidemiological evidence pointing to an increased risk for mother and baby as a pregnancy continues beyond 40 weeks but the data included both induced labours and spontaneous labours; the absolute risk of perinatal death associated with prolonged pregnancy is low at 2-3 per 1000.(NICE-UK, 2008b) A policy of induction of labour at 41 weeks gestation compared to expectant

management is associated with fewer perinatal deaths without increasing the Caesarean delivery rate.(Gulmezoglu, Crowther, & Middleton, 2006) Amongst women who had spontaneous onset of labour, 22.4% started labour only at or after 41 weeks gestation.(NHS_Information_Centre, 2011) Many of these women will need labour induction for prolonged pregnancy with a policy of elective labour

induction from 41⁺⁰ weeks gestation as recommended by NICE UK

guideline(NICE-UK, 2008b). Simple measures particularly home remedies (e.g.

coitus) that effectively facilitate labour in late term before 41 or 42 weeks gestation may be an economic way to reduce the need for labour induction indicated by prolonged pregnancy.

4.5.1.1. Coitus to Facilitate Onset of Labour

Coitus is widely believed by women to hasten the onset of labour.(Schaffir, 2002) Coitus during pregnancy is safe with no effect on perinatal mortality.(Klebanoff, Nugent, & Rhoads, 1984) Coitus during pregnancy is not associated with preterm labour (Berghella et al., 2002; Kurki & Ylikorkala, 1993; Sayle, Savitz, Thorp, Hertz-Picciotto, & Wilcox, 2001) (even in the context of a twin

pregnancy(Neilson & Mutambira, 1989)) or with premature rupture of membranes(Ekwo, Gosselink, Woolson, Moawad, & Long, 1993).

Coitus can increase uterine activity in women at higher risk of preterm labour compared to controls(Brustman, Raptoulis, Langer, Anyaegbunam, & Merkatz, 1989) suggesting that in women on the cusp of labour, coitus may tip such women into labour but would otherwise have little effect in women distant from their natural onset of labour. This rationale opens the potential for coitus to facilitate labour in women at term.

Despite widespread folk belief in the ability of coitus to expedite onset of labour(Schaffir, 2002), there were very few studies on the effect of coitus in

initiating labour at term.(Tan, Andi, et al., 2006) Antenatal care guideline advice from the National Institute for Health and Clinical Excellence, UK (2008) states that “Pregnant woman should be informed that sexual intercourse in pregnancy is not known to be associated with any adverse outcomes” indicating it is safe.

(NICE-UK, 2008a)

The candidate and co-investigators performed an original prospective study on the effect of coitus on onset of labour at term gestation with strongly positive findings.(Tan, Andi, et al., 2006) There was no data from randomised trials on recommending/advising coitus as an intervention to facilitate labour at term until we undertook two such clinical intervention trials(Tan, Yow, et al., 2007) (Omar et al., 2013) with negative findings. In addition a secondary analysis of the earlier trial’s data(Tan, Yow, et al., 2009) was also performed as a sensitivity as well as a hypothesis generating exercise with somewhat surprising and counterintuitive findings of an inverse correlation between coitus and earlier onset of labour.(Tan, Yow, et al., 2009)