Modifiable determinants of newborn macrosomia and birth complications

Globally the incidence of macrosomic newborns is increasing. In Norway the percentage of newborns weighing 4,000g or more has increased from 16 to 20% in less than three decades. Newborn macrosomia is associated with short-and long-term health risks for the infant, and increases the prevalence of birth complications. Parity, maternal age and gender of the child influence fetal growth. Maternal overweight is a risk factor for gestational diabetes (GDM) and newborn macrosomia. Some women with high body mass index (BMI) give birth to macrosomic newborns while others do not. Maternal lifestyle factors are potential predictors of pregnancy complications. Boys are heavier at birth than girls, but girls have higher fat mass at birth than boys. During the period of 2002 and 2005 the STORK-study followed a total of 553 pregnant women through pregnancy and childbirth at the Department of Obstetrics and Gynecology, Rikshospitalet. The aims of this thesis were to evaluate the contribution of modifiable factors that may influence the risk of fetal macrosomia. The first aim was to explore the roles of physical inactivity, BMI and fasting plasma glucose. A second aim was to study the impact of physical inactivity on delivery complications. The third aim was to examine whether maternal fasting plasma glucose levels influence birth weight in the two sexes differently. Pregestational physical inactivity, glucose and high BMI were independent determinants of fetal macrosomia. Pregestational physical inactivity increased the risk of perineal laceration degree three to four. Overweight women with an increase in fasting plasma glucose from early to late pregnancy had a 4.5-fold increase in risk of newborn macrosomia compared to the remaining group with a high BMI. The effect of maternal fasting plasma glucose on birth weight in girls was twice as high as in boys. Paternal birth weight was significantly associated with birthweight of boys, but no such association was seen for girls