Position and Integrity of Uterine Scar Are Determined by Degree of Cervical Dilatation at Time of Cesarean Section

Abnormally invasive placenta (AIP) is a rare and sometimes fatal condition during pregnancy. Abnormally invasive placenta usually is caused by placental implantation over a uterine scar from a previous uterine surgery, most commonly a cesarean section (CS). Abnormally invasive placenta has a maternalmortality rate as high as 5% when undiagnosed. The greatest risk factors for AIP are placenta previa and cesarean delivery in a prior pregnancy. The primary objective of this study was to determine the location of the CS scar in postpartum women who delivered by prelabor or early-labor CS or by intrapartum CS. The secondary objective was to assess the existence of a scar niche in these patients. This study was conducted at the Kasr Al-Ainy UniversityHospital, Cairo, Egypt between March 2019 and December 2019. The researchers prospectively recruited women who underwent a first CS at term. Exclusion criteria were women who delivered preterm or who had had a prior CS. All women were recruited postnatally after a lower-segment CS and had transvaginal ultrasound at 3 months postpartum in order to determine scar position relative to the internal cervical os, as well as to assess the presence of a scar niche. The niche was defined as an anechoic defect with a depth of at least 2 mm in the anterior wall of the lower uterine segment. In all, 407 pregnant women were consented for the study. These women were divided into 3 different groups based on the timing of the cesarean delivery: 103 had a cesarean prelabor or at cervical dilation <= 2 cm, 261 with cervical dilation 3-7 cm, and 43 with cervical dilation >= 8 cm. There were no statistically significant differences in maternal age, body mass index, or ethnicity. There were, however, differences between the groups when considering parity, indication for CS, and station of the fetal head and cervical dilation at the time of delivery. There was also no statistically significant difference between the 3 groups in terms of interval between delivery and timing of the follow-up ultrasound. The study found a significant correlation between cervical dilation at the time of CS and the position of the scar. In 97.1% of women who delivered before labor or at 0-2 cm dilation, the scar was located in the uterus above the internal cervical os, whereas in 97.7% of women delivered at 8-10 cm dilation; the scar was located at the internal os or in the endocervical canal. Women with a cesarean scar above the internal os were more likely to have a niche than women with a cesarean scar below the internal os. These data highlight that the position of a uterine CS scar depends on cervical dilation at the time of CS. The formation of a niche was seen in 40% of scars above the internal cervical os and <20% of scars at or below the internal cervical os.