Estimated fetal weights versus birth weights: should the reference intrauterine growth curves based on birth weights be retired?

Presentation of intrauterine or fetal growth in the form of centile curves based on birth weight was first reported by Lubchenco and her co-workers in 1963.1 In that publication, data on the birth weights of 5635 live born Caucasian infants 24 to 42 weeks of gestation were analyzed. The data were presented in figures and tables that displayed smoothed 10th, 25th, 50th, 75th and 90th percentiles for males and females together and separately. The authors acknowledged several limitations to their analysis, including: “The sample has an undeterminable bias because premature birth itself is probably related to unphysiological states of variable duration in either mother or fetus. Since the weight of fetuses who remain in utero cannot be measured, the curves presented herein are submitted with these reservations as estimates of intrauterine growth.” Nonetheless, the authors felt that the curves would be useful at birth, providing information about the infant’s intrauterine environment and revealing whether he was large or small for his gestational age, and useful after birth to monitor and compare postnatal growth to intrauterine growth. A subsequent paper2 introduced the terms small for gestational age (SGA), appropriate for gestational age (AGA), and large for gestational age (LGA) into our lexicon.

Publication of the Lubchenco curves1,3 was followed by the publication of a number of body weight by gestational age curves that described fetal growth for various populations, ethnic groups, and geographic locations, including North America, Europe, and Australia.4,5,6,7,8,9,10,11,12,13 In addition to the concerns noted above, the influence of two other limitations on body weight means, standard deviations, and percentile values has been acknowledged: (a) inaccurately determined …