Caesarean section operation is not associated with myometrial hypertrophy-a prospective cohort study

Maternity statistics of England in 2020 showed rise in Caesarean Section (CS) rate to 31%. Some studies correlated adverse gynaecological symptoms e.g. menstrual irregularities and pelvic pain to 'niche' formation at CS scar site. Niche formation was speculated to cause myometrial hypertrophy aggravating these symptoms. This was a prospective comparative histological study including 52 consecutive benign hysterectomy specimens which were categorised into 2 groups: (i) specimens with CS scar (n = 22), (ii) specimens with no CS scar (n = 30). Median (IQ range) uteri weight was 97.2grms (43.5-226) and 91.7grms (35.7-201.7) in study and control groups, respectively (p = .991). Mean (±SD) thickness of anterior myometrial wall was 18.7 mm (±3.6) and 19.4 mm (±4.5) in study and control groups, respectively (p = .58). Mean (±SD) thickness of posterior myometrial wall was 19.1 mm (±3.7) and 18.7 mm (±3.9) in study and control groups, respectively (p = .78). The assumption that CS scar causes myometrial hypertrophy was not demonstrated in this study.IMPACT STATEMENTWhat is already known on this subject? Maternity statistics world-wide show a continuous rise in the rate of Caesarean Section (CS) operation. The CS scar is assumed to be related to adverse clinical gynaecological symptoms such as intermenstrual bleeding, dysmenorrhoea, dyspareunia and chronic pelvic pain; however, the mechanism of this association is not clear. Further, little is known about the effects of CS scar on uterine wall morphology and function.What do the results of this study add? This study was the first prospective series in the literature to compare the uteri with scar with those without in respect of weight and myometrial wall thickness. It was not able to demonstrate the association between having CS scar and myometrial hypertrophy which was hypothesised to be the cause of adverse gynaecological symptoms. However, the microscopic examination of the CS scar revealed adenomyosis, haemorrhage and/or chronic inflammation in most cases.What are the implications of these findings for clinical practice and/or future research? The clinical implication of the histological changes shown in the CS scar requires large comparative clinical studies.