Primary Prevention of Gestational Diabetes Mellitus and Large-forGestational-Age Newborns by Lifestyle Counseling: A Cluster-Randomized Controlled Trial

Background: Our objective was to examine whether gestational diabetes mellitus (GDM) or newborns ’ high birthweight can be prevented by lifestyle counseling in pregnant women at high risk of GDM. Method and Findings: We conducted a cluster-randomized trial, the NELLI study, in 14 municipalities in Finland, where 2,271 women were screened by oral glucose tolerance test (OGTT) at 8–12 wk gestation. Euglycemic (n = 399) women with at least one GDM risk factor (body mass index [BMI] $25 kg/m2, glucose intolerance or newborn’s macrosomia ($4,500 g) in any earlier pregnancy, family history of diabetes, age $40 y) were included. The intervention included individual intensified counseling on physical activity and diet and weight gain at five antenatal visits. Primary outcomes were incidence of GDM as assessed by OGTT (maternal outcome) and newborns ’ birthweight adjusted for gestational age (neonatal outcome). Secondary outcomes were maternal weight gain and the need for insulin treatment during pregnancy. Adherence to the intervention was evaluated on the basis of changes in physical activity (weekly metabolic equivalent task (MET) minutes) and diet (intake of total fat, saturated and polyunsaturated fatty acids, saccharose, and fiber). Multilevel analyses took into account cluster, maternity clinic, and nurse level influences in addition to age, education, parity, and prepregnancy BMI. 15.8 % (34/216) of women in the intervention group and 12.4 % (22/179) in the usual care group developed GDM (absolute effect size 1.36, 95 % confidence interval [CI] 0.71–2.62, p = 0.36). Neonatal birthweight was lowe