Doctors do not agree on whether ultrasound should be used routinely or not, and scientific proof that routine use is justified is still lacking.

Four studies have been done comparing the outcome for groups of women who had US to groups of women who didn't. Only one study was thought to be supportive of routine US. All four studies had small numbers, even when pooled. Also the studies have been criticized because of varying design quality and outcomes studied.

A larger study has just been completed in the Helsinki area of Finland. It involved about 10,000 women. These were divided into two groups of 5,000 for comparison, one to receive ultrasound, one control group not scheduled for US. However, 75 percent of women in the control group had already received an ultrasound exam before the study started. The study found that there were no differences in birth weights or number of labour inductions in the two groups. There was no statistical difference in the outcome for the babies in the two groups, if babies that were aborted due to major fetal malformations detected during US were subtracted. In other words, the main value of the US shown in this study was to detect major fetal malformations and give the parents the choice of whether to abort.

The National Institute of Child Health and Human Development in the U.S. has funded a 12 million dollar landmark study on the value of routine ultrasound, co-ordinated by Dr. Bernard Ewigman, Professor at the University of Missouri-Columbia School of Family and Community Medicine. Over 15,000 women were enroled in this study. One group received two ultrasound exams, one at 18 to 22 weeks and one at 31 to 35 weeks. The other mothers received no routine ultrasound, only selective ultrasound.

In September 1993, the New England Journal of Medicine (NEJM) published the results of this study. The study found no difference between the two groups for the rate of death or complications in the newborn. The rates of premature delivery and birth weights were nearly identical in the two groups. There were also no difference in outcome for post-date pregnancies, twins and small for dates infants. To date, there is no conclusive evidence that routine ultrasound improves the outcome for the baby.

However, as an editorial in the same issue of the NEJM comments, the principal benefit of routine ultrasound is the detection of birth defects. This might be of psychological benefit to women and may have a favourable effect on the outcome of some pregnancies.

What The Experts Say

In 1981, the Society of Obstetricians and Gynecologists of Canada stated that, "at the present time data are not yet available to permit the conclusion that diagnostic ultrasound is without any adverse biological effect." It went on to state that the routine use of ultrasound could not be recommended.

The American Institute of Ultrasound in Medicine (AIUT) and the American College of Obstetrics and Gynecology have also recommended ultrasound be used only if problems develop or are suspected during pregnancy.

In Britain, the Royal College of Obstetricians and Gynecologists has recommended a single ultrasound in every pregnancy to estimate fetal age. In West Germany, the recommendation was for two ultrasound exams in every pregnancy.

In 1984, the National Institute of Health (N.I.H.) in the United States sponsored an international conference on the use of ultrasound in pregnancy. Since there was no proof that routine screening made pregnancy safer for either mother or baby, and because of an unproven but possible risk to the fetus, the experts concluded they could not recommend routine screening.

In 1992 the Canadian Periodic Health Examination Update concluded there was "fair" evidence to suggest a single routine ultrasound examination during pregnancy.

Selective Use Of Ultrasound

The N.I.H. conference also listed those medical reasons for which ultrasound would be recommended. Some of the main ones are listed below.

• Threatened miscarriage, tubal pregnancy and fetal death.