Large fetal size in early pregnancy associated with macrosomia

To assess if fetal size at the time of ultrasound dating examination is associated with the risk of macrosomia and complications associated with macrosomia.

This was a retrospective cohort study of 19 377 singleton pregnancies dated in gestational weeks 16-20 during the period 1998-2004 at Danderyd Hospital, Stockholm, Sweden. Obstetric outcome was assessed through linkage to the Swedish Medical Birth Register.

When fetuses were > or = 7 days larger than expected at dating, compared with the expected size according to last menstrual period, there was a 59% increase in the risk of birth weight > or = 4500 g and a 145% increase in the risk of birth weight > or = 5000 g (odds ratio (OR), 1.59; 95% CI, 1.12-2.24 and OR, 2.45; 95% CI, 1.22-4.90, respectively). For a birth weight of > or = 4000 g the risk estimate was 1.19 (95% CI, 0.96-1.47).

Fetuses that are larger than expected in the second trimester have an increased risk of macrosomia. This emphasizes that fetal size in early pregnancy is not only a function of gestational duration, but also of fetal growth. However, only a limited proportion of all infants born macrosomic can be identified as such at the time of ultrasound dating.