Characterisation of the possible effect on birthweight following frequent prenatal ultrasound examinations.

The objective of this study was to evaluate and characterise by study of newborn biometry a possible effect on birthweight which we observed previously in a randomised controlled trial of multiple prenatal ultrasound examinations. A total of 2743 women with single pregnancies had been allocated at random to either a protocol of ultrasound imaging and continuous wave Doppler studies at 18, 24, 28, 34 and 38 weeks gestation (intensive group), or to a protocol of a single imaging examination at 18 weeks and further imaging scans only as clinically indicated (regular group). When compared with those in the regular group, and adjusted for other confounding variables, normally formed babies of term gestational age in the intensive group tended to be shorter when measured at birth (P = 0.123) and on day 2-3 of age (P = 0.068). There were statistically insignificant reductions in the circumferences of the chest, abdomen and mid-arm; and in the skinfold thicknesses of the triceps, parascapular and subscapular regions. Principal component analysis showed a trend for a reduction for the skeletal component (P = 0.085) but not for the soft tissue component (P = 0.332). Comparison of the neonatal biometry in the two groups is not conclusive, but the differential effects on the various growth parameters suggest that if multiple scans do indeed restrict fetal growth, the mechanism is more likely to be an effect on bone growth rather than a reduction in nutrient supply from the placenta.