Routine ultrasound screening in pregnancy and the children's subsequent handedness

This publication describes a follow-up survey study of parents of children of ages 8 to 9 years who participated in a randomized clinical trial for prenatal screening ultrasound.(5) These subjects were identified in 3 clinics in Sweden between October 1985 and March 1987, and 4997 women were randomly assigned to 1 of 2 groups on the basis of their anticipated screening with ultrasound at approximately 15 weeks. The resulting groups excluded women scheduled for ultrasound examination based on clinical indication and therefore were considered low-risk pregnancies. Singleton offspring were followed up at 8 to 9 years, and parents were surveyed about dominant hand and foot use with 10 questions similar to those used in a previous study(6) and 1 additional question; these questions were based on common tasks at this age. The responses were scored numerically as follows: 1, always right hand (or foot); 2, most often right hand (or foot); 3, equally often either hand (or foot); 4, most often left hand (or foot); and 5, always left hand (or foot). Parents were instructed not to answer if they had not observed the child perform the task. Surveys were included in the analysis if at least 10 of 11 questions were answered. Scoring 10 of 11 questions as either 1 or 2 was considered right-handed, and scoring of 4 or 5 was considered left-handed. Those not scored as right-handed were considered non-right-handed together with the left-handed. The researchers had information on a number of possible confounding variables, such as family history of left-handedness, maternal smoking, and sociodemographic variables, although it should be noted that, in this follow-up for a randomized study, there is no good reason to suppose that any potentially confounding variables were differentially distributed by ultrasound exposure status. Three main analyses were conducted. First, the group randomly assigned to ultrasound was compared with the group randomly assigned to no ultrasound, regardless of whether the mother received ultrasound (intention-to-treat analysis). Second, the group who received any ultrasound before 19 weeks' gestation was compared with the group who did not receive any ultrasound before 19 weeks (as-treated analysis). Third, these analyses were stratified by the sex of the child. A statistically significant increase in non-right-handedness was found only for boys in the as- treated comparison (OR, 1.30; 95% CI, 1.01-1.69). This estimate was robust to inclusion of potential confounding factors in a multivariable model.