The value of ultrasound indicators in early pregnancy for predicting selective intrauterine growth restriction and twin–twin transfusion syndrome: a case‒control study

Selective intrauterine foetal growth restriction (sIUGR) and twin–twin transfusion syndrome (TTTS) are common complications in Monochorionic diamniotic (MCDA) twin pregnancies. Timely and accurate diagnosis and intervention are essential to improve perinatal outcomes. The purpose of this study was to determine the value of differences in crown - rump lengths (CRL) and nuchal translucency (NT) and evaluate the significance of differences in embryo length in predicting the occurrence of sIUGR and TTTS. This research is a retrospective study that includes cases of MCDA twins diagnosed via ultrasound in the Obstetrics Department of Shandong Provincial Hospital Affiliated to Shandong University from January 2017 to March 2024. These cases were categorized into sIUGR group, TTTS group, TTTS with sIUGR group and normal MCDA group, based on the presence of complex twin related complications. For each group, embryo length, CRL and NT measured by ultrasound during the 7–14 week gestation period were respectively recorded. The differences in embryo length, CRL and NT between the normal MCDA twin group and sIUGR group, TTTS group, as well as TTTS with sIUGR group were compared. The Mann‒Whitney U test and the chi‒square test were utilized for the analysis. Furthermore, the receiver operating characteristic (ROC) curve was plotted to conduct further analysis. A total of 722 MCDA twins (203 with sIUGR, 158 with TTTS, 55 with TTTS with sIUGR and 306 controls) were included. The difference in the CRL in the sIUGR group (9.43%) was significantly greater than that in the control group (3.30%) (P < 0.001). However, no statistically significant difference in NT or embryo length was detected (P = 0.271, 0.567). The difference in CRL could not be used to distinguish between sIUGR-type I and sIUGR-type II/III (P = 0.35). ROC analysis revealed that the difference in CRL predicted sIUGR with an area under the curve of 0.78; for comparison, the area under the curve for the prediction of TTTS was 0.51. The prediction of sIUGR using the CRL difference threshold of 7.38% had a sensitivity of 80.72% and a specificity of 67%, a positive predictive value (PPV) of 67%, and a negative predictive value (NPV) of 80.72%. In MCDA twin pregnancies, the difference in the first-trimester CRL was valuable for predicting the occurrence of sIUGR but was not associated with TTTS. Embryo length and NT did not significantly differ among the groups. Not applicable.