P01.11: Comparison between first and third trimester evaluation of uterine scar: a prospective study

Abstract

Third trimester evaluation of low-uterine segment (LUS) thickness can be used to predict uterine scar defect and uterine rupture during labour. We aim to estimate its correlation with remaining myometrium thickness (RMT) in the first-trimester. Women with a single previous low-transverse Caesarean were recruited at 11–14 weeks' gestation. Measurement of RMT at the site of uterine scar was obtained for each participant and they were invited to come back for a second evaluation at 34–36 weeks gestation, for measurement of the LUS thickness. Comparisons between the first trimester RMT and third trimester LUS thickness were performed using Pearson and Spearman's correlation tests. Data were available for 129 (70%) out of 184 participants recruited at a mean gestational age of 12.7±0.5 weeks and seen again at 36.3±0.7 weeks of gestation. The mean first trimester RMT 6.3±3.2 mm, and the mean third trimester LUS thickness was 4.0±1.8 mm. We observed no significant association between first trimester RMT and third trimester LUS thickness (cc: 0.05 and cc: 0.10, with p>0.05 for both analyses). Three participants had a first trimester RMT<2.0 mm, which could have predicted 10% (1/10) of those with third trimester LUS thickness <2.0 mm. There is a poor correlation between first and third trimester evaluation of low-uterine segment thickness in women with previous Caesarean. First trimester evaluation of low-uterine segment thickness should not be used to counsel women about the risk of uterine rupture during a trial of labour.