Ultrasound Studies of Caesarean Hysterotomy Scars
Abstract: The aim of the work presented in this thesis was to investigate how transvaginal ultrasound examination of non-pregnant women could be used to visualize and assess caesarean hysterotomy scars, and to evaluate the risk of uterine rupture in subsequent pregnancies. The diagnostic value of transvaginal ultrasound for correct evaluation of caesarean hysterotomy scars was determined, and the prevalence of defective scars was estimated. A scar defect was defined based on the thickness of the myometrium covering the defect. One fifth of the women who had undergone a caesarean delivery were found to have a large defect. The proportion of women with large scar defects increased with the number of caesarean deliveries (14% in women after one caesarean compared with 21% after two caesareans, and 46% in those who had undergone three or more caesareans; p=0.029). It was found that hysterotomy scars after caesareans are better evaluated by ultrasonography in combination with hydrosonography than conventional ultrasonography. Scars with defects were found to be located lower in the uterus than intact scars. The median distance between the internal cervical os and an intact scar was 4.6 mm and between the internal cervical os and a deficient scar 0 mm. A multivariate logistic regression model, including clinical information and ultrasound variables, of women who underwent a transvaginal ultrasound scan after their first caesarean delivery was used to identify factors affecting the risk of large defects in caesarean hysterotomy scars. Caesarean deliveries performed in advanced labour increased the likelihood of a large scar defect (the later, the higher the risk), and the risk increased drastically when the caesarean was performed when the cervix was dilated by 5 cm or more. Two out of ten (2.2%) of the women who had intact uterine scars or small defects, as indicated by transvaginal ultrasound, suffered uterine dehiscence or uterine rupture in their first delivery after the scan, versus 23.1% of the women with large defects (p=0.018). This suggests that large defects in the hysterotomy scar after caesarean delivery, detected by transvaginal ultrasound in non-pregnant women, increase the risk of uterine rupture or dehiscence in subsequent pregnancies.
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