Trends in risk factors associated with the increasing labor induction rate: A nationwide register study in Finland...

Induction of labor (IOL) rates have been increasing in high-income countries. Although IOL aims to reduce maternal and neonatal morbidity, the benefits for many common indications remain uncertain. Because IOL may also have disadvantages and place a burden on the health-care system, it is important to clarify the factors underlying the rising national IOL rates.

This descriptive study included all singleton births in cephalic presentation delivered at 37⁺⁰ gestational weeks or later between January 1, 2005, and December 31, 2023, in Finland. Data from the Finnish Medical Birth Register were used to examine temporal trends in maternal characteristics, gestational age at delivery, pregnancy complications, and other pregnancy-related problems across three periods: 2005-2010, 2011-2016, and 2017-2023. Induced deliveries were analyzed separately. Risk ratios with 95% confidence intervals were calculated to describe changes over time, and odds ratios with 95% confidence intervals were estimated to assess associations between IOL and risk factors. Logistic regression models were adjusted for maternal age, body mass index (BMI), and parity.

The study sample included 880 478 births. The IOL rate doubled from 18% to 36%. In the IOL group, the most prevalent and increasingly common factors were maternal age ≥35 years, BMI ≥30 kg/m², and gestational diabetes. Prelabor rupture of membranes, fear of childbirth, and other pregnancy-related problems-despite their lower overall proportions-showed the steepest increases. Similar but less pronounced trends were seen in the total study cohort. The odds of IOL remained stable across the study periods for maternal age ≥35 years, BMI ≥30 kg/m², gestational diabetes, prelabor rupture of membranes, fear of childbirth, and other pregnancy-related problems; and all associations remained statistically significant after adjustment. The proportion of post-term pregnancy decreased significantly in both the total study cohort and the IOL group. In the IOL group, gestational age at birth shifted from post-term to late- and full term.

The main contributors to the increasing IOL rate were the increased prevalence of advanced maternal age, obesity, and gestational diabetes. The increases in the prevalence of other IOL indications were less extensive.