Development of a rabbit model of uterine rupture after caesarean section, histological, biomechanical and polarimetric analysis of the uterine tissue.

Abstract: Uterine rupture is a major complication of caesarean section (CS) associated with high fetal and maternal morbidity. The objective is to develop an in vivo model of uterine healing and rupture after CS in order to analyse histological phenomena controlling scarring tissue development and potential causes of defects. Eighteen pregnant primiparous female rabbits were bred naturally. At caesarean, after 28 days of gestation, foetuses were either extracted through a longitudinal incision in one of the uterine horns ('CS horn') or via a short incision at the tip of the contralateral horn ('control horn'). The uterine horns were sutured in a single layer, all by the same surgeon. They were mated again 14 days later and euthanised at G28. Genital tracts were collected for histological, biomechanical and polarimetric analyses. Macroscopically, 2/18 presented a dehiscence and 1/18 a spontaneous rupture. The mean thickness of the scarred area was significantly lower, 0.9 mm (0.7-1.4), than the non-scarred area on CS horns 2.2 (1.6-2.3) or control horns 2 (1.5-2.3) (P < 0.0001). The scar zone was statistically more fibrous (P < 0.0001), containing fewer vessels (P = 0.03), oestrogen receptors (P < 0.001) and progesterone receptors (P < 0.0001). After balloon inflation, rupture occurred in the scar zone in 8 out of 17 cases (47%). Polarimetry revealed that the scar zone was statistically inhomogeneous (73%). Multifactorial analysis identified groups with poor uterine healing and less resistance to rupture (balloon inflation), mostly in cases of thin myometrium in the scar, and a group with strong resistance to rupture and correct healing characteristics. Lay summary: CS rates are rising across the world. When a CS is carried out, it can lead to scarring on the uterus that can affect its resistance to pressure. During the next pregnancy, the uterus can tear, increasing risks to the mother and baby. We carried out CSs in rabbits, allowing us to analyse the scar on the uterus, the healing and tissue resistance. The scarred part of the uterus was statistically thinner, more fibrous and contained fewer vessels and hormone receptors than the area without scarring. Under similar conditions, poor healing was observed in some animals, reducing resistance in following pregnancies. These results suggest that individual and genetic factors have an effect on healing after a CS. This study may improve our knowledge and management of care for patients who have a CS in order to reduce complications.