Is an ultrasound assessment of gestational age at the first antenatal visit of value? A randomised clinical trial.

Objectives: To assess the efficacy of an ultrasound scan at the first antenatal visit.

Design: Randomised clinical trial.

Setting: Women's and Children's tertiary level hospital, Adelaide, Australia.

Population: Six hundred and forty-eight women attending for their first antenatal visit at less than 17 weeks of gestation who had no previous ultrasound scan in the pregnancy, who were expected to give birth at the hospital, and for whom there was no indication for an ultrasound at their first visit.

Methods: Eligible consenting women were enrolled by telephone randomisation into either the ultrasound at first visit group, who had an ultrasound at the time of their first antenatal visit, or the control group in whom no ultrasound assessment was done at their first antenatal visit. Both groups of women completed a questionnaire at the end of the first visit on their feelings towards the pregnancy and anxiety levels. Data were collected on details of any ultrasound assessments, including the 18 to 20 weeks morphology scan, and pregnancy outcome. All primary analyses were on an intention-to-treat basis.

Main Outcome Measures: The number of women who needed adjustment in dates of 10 days or more on the basis of their 18 to 20 weeks ultrasound morphology scan, who were booked for their morphology scan at sub-optimal gestations, who had a repeat of their maternal serum screening test, or who felt worried about their pregnancy at the end of the first antenatal visit.

Results: Fewer women (9%) in the ultrasound at first visit group needed adjustment of their expected date of delivery as a result of the 18 to 20 week ultrasound, compared with 18% of women in the control group (RR 0.52, 95% CI 0.34-0.79; P = 0.002). The number of women who had the 18 to 20 week ultrasound assessment timed suboptimally was similar to that in the control group (16% vs. 21%), as was the number of women who had a repeat blood sample taken for maternal serum screening (6% vs. 6%). Fewer women in the ultrasound at first visit group reported feeling worried about their pregnancy (RR 0.80, 95% CI 0.65-0.99; P = 0.04) or not feeling relaxed about their pregnancy (RR 0.73, 95% CI 0.56-0.96; P = 0.02), compared with women in the control group.

Conclusions: A routine ultrasound assessment for dating offered to women at the first antenatal visit provides more precise estimates of gestational age and reduces the need to adjust the estimate of the date of delivery in mid-gestation. Women who had an ultrasound at the first visit reported more positive feelings about their pregnancy, compared with women in the control group at that time.