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Keywords:

  • Induction of labour;
  • Labour;
  • pregnancy;
  • ultrasound

Objective  To evaluate the effect of a first trimester ultrasound dating scan on the rate of induction of labour for prolonged pregnancy.

Design  Randomised controlled trial to include 400 women in each arm of the trial.

Setting  Participating general practices and a district general teaching hospital.

Population  Women attending their general practitioner in the first trimester to confirm pregnancy, in whom a first trimester ultrasound scan was not indicated.

Methods  Women randomised to the study group (scan group) underwent an ultrasound dating scan between 8 and 12 weeks, measuring crown-rump length. The estimated date of delivery (EDD) was changed if there was a discrepancy of more than 5 days from the gestation, calculated from the last menstrual period (LMP). For the remaining women (no-scan group), gestation was determined using the LMP.

Main outcome measures  The rate of induction of labour for prolonged pregnancy.

Results  Due to circumstances beyond the researchers’ control, recruitment was abandoned when 463 women had been enrolled. The EDD was adjusted in 13 (5.7%) women in the scan group and in 2 (0.9%) in the no-scan group. There was no difference in the rate of induction for prolonged pregnancy between the scan (19 [8.2%]) and the no-scan (17 [7.4%]) groups (relative risk 1.10; 95% CI 0.59–2.07).

Conclusions  Acknowledging the reduced numbers recruited for study, it is concluded that there is no evidence that a first trimester ultrasound dating scan reduces the rate of induction of labour for prolonged pregnancy and may result in a more expensive healthcare strategy.