BJOG. 2006 Feb;113(2):171-6.
Does a first trimester dating scan using crown rump length measurement
reduce the rate of induction of labour for prolonged pregnancy? An
uncompleted randomised controlled trial of 463 women.
Harrington DJ, MacKenzie IZ, Thompson K, Fleminger M, Greenwood C.
Department of Obstetrics and Gynaecology, The Women's Centre, John
Radcliffe Hospital, Oxford, UK.
Objectives:
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.
