Maternal risk factors and their influence on fetal anthropometric measurements

Our purpose was to determine if and when maternal risk factors and fetal sex have an impact on specific fetal anthropometric measurements assessed by ultrasonography.

Serial ultrasonographic examinations were performed on 1205 fetuses of indigent multiparous women who ultimately gave birth at term. Femur length, abdominal circumference, and head circumference measurements were obtained at mean gestational ages of 18, 25, 31, and 36 weeks, and an estimated fetal weight was calculated. At birth the infant was weighted and head circumference, abdominal circumference, femur length, and crown-heel length measurements were made. Regression analyses were used to determine the effect on each measurement of maternal race, height, body mass index, hypertension, weight gain, smoking, previous low birth weight, and fetal sex.

Acting through their effect on head circumference, abdominal circumference, and fetal length, each of the risk factors and female sex were shown to have a negative effect on fetal weight. The timing of the impact, its magnitude, and the specific anthropometric measurement affected were different for each of the risk factors.

The impact of maternal risk factors and fetal sex on estimated fetal weight has been demonstrated to occur first in specific gestational age windows and is mediated through effects on specific fetal anthropometric measurements.