The outcome of macrosomic fetuses in a low risk primigravid population.

OBJECTIVES: To ascertain whether fetal macrosomia is associated with increased maternal and neonatal morbidity in uncomplicated, singleton, vertex deliveries at term in primigravid women.

METHODS: This was a retrospective population based survey of 8617 deliveries over an 11-year period. These were stratified into three birthweight categories: 2500-3999 g (n=7854), 4000-4499 g (n=666) and > or =4500 g (n=97). Outcome variables included maternal characteristics, delivery details, maternal and perinatal morbidity data.

RESULTS: Increased BMI and incidence of Caucasian ethnicity and non-smoking were significantly greater in macrosomic compared with non-macrosomic infants (P<0.001). Increasing birthweight (especially > or =4.5 kg) was associated with significantly (P<0.001) lower rates of spontaneous onset of labor, spontaneous vertex deliveries and significantly higher rates (P<0.001) of maternal and neonatal morbidity.

CONCLUSIONS: This study supports the notion of expectant management in suspected fetal macrosomia in low risk primigravid women until 40 weeks gestation. Thereafter, the safest mode of delivery is controversial, with some evidence pointing to elective cesarean section as a viable alternative in these women. A prospective RCT is needed to evaluate the best management option in terms of fetal and maternal outcome in cases of suspected macrosomia after 40 weeks' gestation.