Fig. 4

Maternal metabolites in the second trimester to predict sFGR. A ROC curves of models constructed based on each significantly differential metabolite in the second trimester for the prediction of sFGR. B ROC curves of models constructed based on the combination of significantly differential metabolites for the prediction of sFGR. Eight-AUC presents the predictive effectiveness of the combination of eight significant differential metabolites, including l-proline, l-arginine, l-tyrosine, l-leucine, l-isoleucine, l-phenylalanine, betaine, and TMVAV. Three-AUC presents the predictive effectiveness of optimized combination of three significant differential metabolites, including l-leucine, l-isoleucine, and l-phenylalanine. The dots on the broken lines in B represent the best cut-off value, and the values in the figure represent the best cut-off value (sensitivity, specificity). The shadow around the linear regression trend line shows the 95% confidence interval (CI); The P value in B was shown as the significant difference between model A and model B; P < 0.05 was considered statistically significant. C The correlation between metabolite levels in the second trimester and the difference in physical development parameters of twins were examined by Spearman correlation analysis. Spearman’s correlation coefficients (R) were used to present the correlations, and only R values with P < 0.05 were plotted. sFGR, selective fetal growth restriction; ST, second trimester; TMVAV, N, N, N-trimethyl-5-aminovaleric acid; TMAO, trimethylamine-N-oxide; HC, head circumference; AC, abdominal circumference; BPD, biparietal diameter; FL, femur length; S/D, ratio of fetal umbilical artery systolic pressure to diastolic pressure; ROC, receiver operating characteristic; AUC, area under curve; diff, the difference between the larger and the smaller fetus