Transvaginal evaluation of cesarean section scar niche in a subsequent pregnancy - a prospective longitudinal study

Abstract

Introduction Many studies describing Cesarean section (CS) scars using ultrasonography have been carried out on both: non-pregnant and pregnant status. The visibility and measuring of CS scar on ultrasound examination may be clinically relevant, but still, there is limited evidence relating CS scar niche to pregnancy outcome in a future pregnancy. Aim To investigate the prevalence of Cesarean section (CS) scar niche during pregnancy by transvaginal ultrasound imaging and to relate scar measurements, demographic and obstetric variables and final pregnancy outcome. Methods Methods In this prospective observational study we used transvaginal sonography (TVS) to examine the CS scar of 122 pregnant women at 11+0-13+6, 18+0-20+6 and 32+0-35+6 weeks of gestation. A scar was defined as visible on pregnant status when the area of hypoechogenic myometrial discontinuity of the lower uterine segment was identified. The CS scar niche(“defect”) was defined as an indentation at the site of the CS scar with a depth of at least 2mm in the sagittal plane. The hypoechogenic part of the CS niche was measured in two dimensions as well as the residual myometrial thickness (RMT). In the second and third trimesters of pregnancy, the full lower uterine segment (LUS) thickness as the myometrial layer thickness at the thinnest part of the scar area was measured. In a non-selected subset of patients (n=24) visible CS scars were measured by two independent examiners. Factors that may be associated with CS scar niche including maternal age, BMI, previous vaginal delivery, smoking status, obstetrics complications and a history of previous uterine surgery were investigated. After delivery, information about pregnancy outcomes was retrieved from hospital electronic database records. Results The scar was visible in 95/122 (77.9%) cases. Of those with visible CS scar half of women had CS niche 49/95 (51.6%). Median uterine scar niche length at first trimester was 5.0 (3.90-7.05)mm, depth was 6.9 (4.85-9.70) mm and RMT 4.7 (3.35-5.95) mm. No significant association was found between women subgroups according to CS niche at first trimester and LUS thickness at second (p=0.138) and third (p=0.584) trimester of pregnancy. [...].