When to INDuce for OverWeight? - a Randomised Controlled Trial (WINDOW)

Background The World Health Organization (WHO) defines overweight as a body mass index (BMI) of ≥25 kg/m2 and obesity as a BMI of ≥30 kg/m2. Overweight and obesity are rising dramatically worldwide. In fertile women, the prevalence of obesity is one third in the United States, 20% in the United Kingdom, and 12-13% in Denmark. The association between obesity in pregnancy and the risk of gestational complications increases with increasing BMI. Among other complications, obesity in pregnancy is associated with increased risk of caesarean delivery. Delivery by caesarean section further adds significant risks of wound infection or other infectious morbidity in obese women as compared to normal weight women. The longer the woman is pregnant, the longer the risk of pregnancy complications remains. In an otherwise low-risk pregnant woman at term, it is an on-going clinical dilemma, whether the benefits of elective induction of labor (eIOL) and termination of the pregnancy will outweigh the potential harms from the concomitant induction and delivery process. Regarding delivery complications, based on data from historical cohorts, eIOL has traditionally been associated with an increased risk of caesarean section and instrumental delivery. Therefore, expectant management has been the preferred clinical option. This interpretation has now been challenged by a randomized trial (ARRIVE) with >6000 low-risk pregnant women where eIOL at 39 weeks of gestation was associated with lower caesarean delivery rates. There are no randomized studies in obese women, but two larger observational studies did find lower odds of caesarean delivery in obese women with eIOL as compared to awaiting labor onset. Hence, a randomized trial that would compare caesarean delivery among obese women whose labor is induced with those expectantly managed is warranted. The proposed study will provide new and important knowledge into the area of induction of labor among overweight and obese women with potential great international impact for the future raising number of pregnant women in this subgroup.

With this trial, the investigators aim to compare the risk of caesarean section in obese (BMI ≥ 30 kg/m2), but otherwise low-risk women with eIOL as compared to expectant management.

Materials and methods

The study is a multicenter randomized controlled trial with an allocation ratio of 1:1 in the two following arms:

• Intervention arm/elective induction of labor in pregnancy at 39 gestational week and 0 to 3 days: Induction is performed according to local policy for induction of labor.
• Comparison arm/expectant management: Waiting for spontaneous onset of labor unless a situation develops necessitating either induction of labor or caesarean section.