Thigh circumference and thigh-to-head ratio in preterm and term infants.

The diagnosis of altered fetal growth requires multiple criteria that include not only weight and length measurements, but also head, abdominal, and thigh circumference measurements. This cross-sectional study presents the normal standards for thigh circumference, thigh-to-head ratio, and Rohrer's ponderal index in newborn infants from 27 to 41 weeks' gestation, in relation to gestational age and birth weight. A thigh-to-head ratio of < 0.38 and a ponderal index < 2.3 in a term infant are important measurements for appropriate diagnosis of impaired fetal growth. These standards may also serve as reference for comparison with fetal ultrasonographic measurements.