The relationship of birth weight and intrauterine diagnostic ultrasound exposure.

Imaging with ultrasound is common in obstetric practice. Several laboratory animal studies have shown retardation in fetal growth after experimental ultrasound exposure. This investigation was conducted to determine whether human fetuses exposed to diagnostic ultrasound (sonography) have a greater risk of growth retardation than fetuses not so exposed. This retrospective cohort study compares the birth weights of 1598 exposed and 944 unexposed single live births at the Johns Hopkins Hospital in Baltimore, Maryland during calendar year 1981. Confounding variables, defined as those associated with both exposure status and birth weight outcome, were included in multivariable analysis. Both exposure to more than one ultrasound procedure and first exposure during the third trimester were associated with a reduction in birth weight. However, the most consistent effect associated with birth weight appeared to be the indication for an ultrasound examination. The relationship of ultrasound exposure and reduced birth weight appeared to be due to shared common risk factors, which lead to both exposure and a reduction in birth weight.