[Reducing rate of macrosomia in Iceland in relation to changes in the labor induction rate]

Diabetes and prolonged pregnancy are risk factors of macrosomia. The aim was to explore the relationship between the increased rate of labor induction and macrosomia in Iceland. Changes in the incidence proportion of macrosomia was estimated by gestational age. Further, the association between labor induction and macrosomia was estimated in reference to expectant management.

Data from the Iceland birth registry on 92,424 singleton births from 1997 to 2018 was used in this cohort study. Macrosomia was defined as birth weight more than 4.5 kg. The incidence proportion during three periods, 1997-2004, 2005-2011, 2012-2018, was calculated and stratified by gestational age. The relative risk reduction of macrosomia over time was calculated with log-binomial regression, using the first period as reference. The risk and relative risk of macrosomia compared with expectant management was estimated and adjusted for diabetes.

The total number of macrosomic infants was 5110 and of those only 313 had a mother with diabetes. The incidence proportion of macrosomia was 6.5% during the period 1997-2004, but 4.6% during 2012-2018. A relative risk reduction of macrosomia over time was seen for deliveries after estimated due date. Labor induction decreased the risk of macrosomia, but the association persisted after adjustment for diabetes.

The rate of macrosomia decreased in Iceland during the last two decades, but only a small proportion of macrosomic infants had a mother with diabetes. Labor induction decreased the risk of macrosomia, an association which seemed independent of diabetes.