Study On The Relationship Between The Minimum Myometrial Thickness And Outcome Of Pregnancy Again In The First Trimester After Cesarean Section

Objective:To explore the relationship among the implantation position of pregnancy sac with placental implantation and cesarean scar pregnancy（CSP）in early pregnancy after cesarean section,and to study the application value of minimum myometrium thickness in placental implantation and incisional pregnancy diagnosis and treatment.Methods:From July 2019 to July 2020,pregnant women who underwent ultrasound examination in the first trimester(5～10⁺⁶ weeks)and had at least one cesarean section in Anhui Maternal and Child Care Hospital were selected as subjects,the implantation characteristics of ultrasonic pregnant sac in early pregnancy were recorded:the minimum thickness of uterine myometrium and the distance between the lower edge of gestational sac and the inner orifice of cervix.The clinical data of prenatal examination,ultrasound examination and pregnancy outcome during pregnancy were followed up,and the cases of early abortion,mid-term induced labor,stillbirth and vaginal delivery were excluded.The patients with cesarean scar pregnancy were divided into cesarean scar pregnancy group（CSP group,n=73）.According to the minimum myometrium thickness,the CSP pregnancy group was divided into group I（≤2mm）,II group（2～3mm）and III group（>3mm）.According to the minimum myometrium thickness of early pregnancy,the pregnant women who were terminated by cesarean section in our hospital were divided into group A（≤6mm）and group B（>6mm）.According to the results of clinical diagnosis and placenta pathology,the pregnant women were divided into normal group（n=609）without placenta previa and placenta accreta.Placenta previa group:placenta previa without placenta accreta（19 cases）,placenta accreta group（placenta adhesion,placenta accreta,placenta penetration）（PAS group:19cases）.Rank sum test was used to compare the difference of minimum myometrium thickness between CSP group and normal group,chi-square test was used to compare the proportion of PAS patients with different minimum myometrium thickness,specificity,sensitivity,negative predictive value and positive predictive value of different minimum myometrium thickness were calculated,ROC curve was used to evaluate the accuracy of prediction model,and logistic linear regression model was used to analyze the independent risk factors of placental accreta.Results:In the first part:1.During the study period,a total of 756 pregnant women were enrolled in the follow-up cohort and terminated in our hospital,including 14 cases of spontaneous abortion and missed abortion,73 cases of cesarean scar pregnancy,7cases of mid-term induced labor due to fetal malformation,stillbirth and social factors,15 cases of live delivery through vagina,and 647 cases of pregnant women delivered live babies by cesarean section in our hospital（including 609 cases of normal group and 19 cases of placenta previa without placenta accreta）.Placenta accreta group（n=19）2.The minimum myometrial thickness of 73 patients with CSP was less than that of609 normal patients.The difference was statistically significant（P<0.001）.Taking the minimum myometrium thickness≤6mm as the diagnostic index,the area under the ROC curve was 0.985,the sensitivity was 100%,the specificity was 92.6%,the positive predictive value was 62.0%,and the negative predictive value was 100%.3.According to the comparison of the general clinical data of the three groups of patients with CSP,there was no significant difference in the age,the interval between the last cesarean section and the level of bloodβ-HCG within 24 hours before operation among the three groups（P>0.05）.The pregnancy days of CSP patients in group I were significantly higher than those in II group and III group.The gestational days in CSP group were significantly higher than those in III group（all P<0.017）.4.Comparing the constituent ratio of uterine curettage and vaginal treatment among the three groups of CSP patients,the difference was statistically significant（P<0.001）.The pairwise comparison showed that the constituent ratio of uterine curettage in group I of CSP patients was lower than that of II group,III group,the constituent ratio of CSP patients treated with vaginal surgery I group of CSP patients was higher than that of II group and III group.The difference was statistically significant（all P<0.017）.5.Comparing the pregnancy outcome of 42 CSP patients who underwent uterine curettage,there were significant differences in intraoperative blood loss and hospitalization costs among the three groups of CSP patients.Pairwise comparison showed that the intraoperative blood loss of CSP patients in group I was more than that in II group,III group,I group,CSP group and III group.The difference was statistically significant（P<0.017）.Part II:1.The minimum sagittal muscle thickness of 647 patients was distributed between 1.8～29.5mm with a median of 10.3mm,P₂₅7.7mm,P₇₅13.7mm.2.There was significant difference in the number of previous cesarean sections among the three groups（P<0.017）.It was found that the number of previous cesarean sections in normal group and placenta previa group was lower than that in PAS group（P<0.017）,and the difference was statistically significant（P<0.05）.The number of previous cesarean section in normal group and placenta previa group was significantly lower than that in placenta previa group（P<0.05）.It was found that the times of previous uterine clearance in placenta previa and PAS group were significantly higher than those in normal group（P<0.017）.3.There was significant difference in the distribution of different minimum myometrium thickness among the three groups（χ²=70.2,P<0.001）.Pairwise comparison showed that the distribution proportion of minimum myometrium thickness≤6mm in PAS group was higher than that in normal group,placenta previa group,PAS group was lower than that in normal group and placenta previa group（all P<0.017）.The proportion of placenta previa>6mm in placenta previa group was lower than that in normal group and placenta previa group（all P<0.05）.4.According to the clinical diagnosis and pathological results of placenta,19 cases in PAS group included 13 cases with placental adhesion,4 cases with placental myometrium accreta,2 cases with placental cervix and bladder accreta,and 19 cases with placenta previa without placenta accreta.The gestational weeks of placenta previa in normal group was significantly higher than that in placenta previa group and PAS group（P<0.017）.The gestational weeks in placenta previa group were significantly higher than those in placenta previa group and placenta previa group（P<0.05）..The intraoperative blood loss in PAS group was significantly higher than that in normal group（P<0.017）.The intraoperative blood loss in placenta previa group was significantly higher than that in normal group and placenta previa group（P<0.05）.The intraoperative blood loss in PAS group was significantly higher than that in normal group（P<0.017）.The intraoperative blood loss in placenta previa group was significantly higher than that in normal group（P<0.05）.The proportion of prenatal bleeding in placenta previa group and PAS groupwas significantly higher than that in normal group（all P<0.017）.5.Taking placental accreta as dependent variable,previous cesarean section,anterior wall gestational sac and minimum myometrium thickness as independent variables,binary logistic regression analysis showed that previous cesarean section,previous cesarean section and anterior wall pregnancy sac were independent risk factors of placental accreta（OR=5.654,11.811,3.196,respectively）,and minimum myometrium thickness was protective factor of placenta accreta（OR=0.125）.Conclusions:1.Ultrasonic imaging measurement of minimum sagittal muscle thickness≤6mm can be used as one of the indexes for the diagnosis of cesarean section scar pregnancy.2.Uterine curettage is not recommended for CSP patients with minimum sagittal muscle thickness≤2mm.3.For women with a history of cesarean section,if the minimum sagittal muscle thickness≤3 mm in the first trimester(5～10⁺⁶ weeks),the risk of placental accreta is significantly increased,especially in pregnant women with multiple cesarean section and uterine clearance history.Placental accreta is more likely to occur.4.After the pregnancy again of pregnant women with scar uterus,the measurement of the minimum myometrium thickness in the first trimester(5～10⁺⁶ weeks)has a certain guiding significance for predicting the outcome of pregnancy.