Rate of postdates induction using first-trimester ultrasound to determine estimated due date: Wellington Regional Hospital audit

Aim: The aim of this audit was to examine the effect of using first-trimester (< 14 weeks) ultrasound scan to determine EDD (US EDD) on the rate of induction for postdates pregnancies at Wellington Regional Hospital. Methods: Women with singleton live pregnancies who had postdates (>= 41 weeks) induction at Wellington Hospital during January 2009 to November 2009 were identified using a computerised database [Perinatal Information Management System (PIMS)]. The first-trimester ultrasound images and reports for these women were retrieved and reviewed by a specialist in obstetric ultrasound. Only ultrasound studies that had technically satisfactory images at < 14 weeks were included. Results: A total of 329 women with a singleton live pregnancy were induced for postdates during the study period. Of these women, 50 (15.2%) were not >= 41 weeks on PIMS EDD and therefore on the best available evidence should not have been induced for being postdates. Of the remaining 279 women, 158 had first-trimester scans available for review. Forty-three of 158 (27%) were < 41 weeks when US EDD was used. Conclusions: The rate of postdates inductions at Wellington NRH could be decreased by 38% if induction was limited to women over 41-week gestation and by using US EDD as opposed to last menstrual period EDD. The use of early gestational scans (< 14 weeks) to estimate EDD lowers the rate of postdates induction. This is very similar to the observed findings in literature.