Fetal abdominal circumference measurements of 35 and 38 cm as predictors of macrosomia. A risk factor for shoulder dystocia.

OBJECTIVE To determine if ultrasound measurements of fetal abdominal circumference (AC) can be used to predict macrosomic infants. STUDY DESIGN Using a computer database, 1,996 women at > or = 36 weeks' gestation, delivering a singleton infant and having an ultrasound examination within one week of delivery were studied. Fetal AC was evaluated to determine if it was useful in predicting the birth of a macrosomic infant, > 4,000 or > 4,500 g. RESULTS AC predicted infants > 4,500 g better than those > 4,000 g. Almost all macrosomic infants > 4,500 g had an AC of > or = 35 cm (68/69, or 99%), but many nonmacrosomic infants were also in this group (683). AC of > or = 38 cm occurred in 99 infants, and 37 of the 69 (53.6%) weighing > 4,500 g were identified. Most infants (78%) with AC > or = 38 cm weighed > 4,000 g. CONCLUSION Fetal AC was very helpful in identifying potential macrosomic infants. If AC was < 35 cm, the risk of infant birth weights > 4,500 g was < 1%. If AC was > or = 38 cm, the risk was 37% (37/99), and > 50% of these infants were identified (37/69, or 53.6%).