RESUMEN
The transition from mafic to felsic upper continental crust (UCC) is crucial to habitability of Earth, and may be related to the onset of plate tectonics. Thus, defining when this crustal transition occurred has great significance for the evolution of Earth and its inhabitants. We demonstrate that V isotope ratios (reported as δ51V) provide insights into this transition because they correlate positively with SiO2 and negatively with MgO contents during igneous differentiation in both subduction zones and intraplate settings. Because δ51V is not affected by chemical weathering and fluid-rock interactions, δ51V of the fine-grained matrix of Archean to Paleozoic (3 to 0.3 Ga) glacial diamictite composites, which sample the UCC at the time of glaciation, reflect the chemical composition of the UCC through time. The δ51V values of glacial diamictites systematically increase with time, indicating a dominantly mafic UCC at ~3 Ga; the UCC was dominated by felsic rocks only after 3 Ga, coinciding with widespread continental emergence and many independent estimates for the onset of plate tectonics.
RESUMEN
BACKGROUND: The effect of gestational weight gain (GWG) as a controllable factor during pregnancy pelvic floor function has rarely been investigated, and studies on twin primiparas are even less frequent. The objective of the present study was to explore the effect of GWG on postpartum pelvic floor function in twin primiparas. METHODS: We retrospectively analyzed the clinical data of 184 twin primiparas in the pelvic floor rehabilitation system of the First Affiliated Hospital of Chongqing Medical University from January 2020 to October 2021. Based on the GWG criteria recommended by the Institute of Medicine, the study subjects were classified into two groups: adequate GWG and excessive GWG. Univariate and multivariate logistic regression models were applied to explore the relationship between GWG and pelvic floor function. RESULTS: Among the 184 twin primiparas, 20 (10.87%) had excessive GWG. The rates of abnormal vaginal dynamic pressure (95% vs. 74.39%), injured type I muscle fibers (80% vs. 45.73%), anterior vaginal wall prolapse (90% vs. 68.90%), and stress urinary incontinence (50% vs. 20.12%) of twin primiparas with excessive GWG were significantly higher than those with adequate GWG. There was no significant difference between the total score of the Pelvic Floor Distress Inventory-Short Form 20 (PFDI-20) or the scores of the Pelvic Organ Prolapse Distress Inventory 6 (POPDI-6), the Colorectal-Anal Distress Inventory 8 (CRADI-8), and the Urinary Distress Inventory 6 (UDI-6) in the two groups (P > 0.05). After adjusting for potential confounding factors, the results showed that excessive GWG was positively associated with abnormal vaginal dynamic pressure (OR = 8.038, 95% CI: 1.001-64.514), injured type I muscle fibers (OR = 8.654, 95% CI: 2.462-30.416), anterior vaginal wall prolapse (OR = 4.705, 95% CI: 1.004-22.054), and stress urinary incontinence (OR = 4.424, 95% CI: 1.578-12.403). CONCLUSION: Excessive GWG in twin primiparas was positively correlated with the prevalence of pelvic floor dysfunction but did not exacerbate pelvic floor symptoms in twin primiparas. Controlling GWG within a reasonable range is recommended for reducing the risk of PFDs in pregnant women with twins.