Risk Factors for Umbilical Artery Thrombosis in Pregnant Women: A Retrospective Study.

Purpose: Umbilical artery thrombosis (UAT) is a rare but potentially life-threatening complication in pregnancy. It shares ultrasonographic similarities with isolated single umbilical artery (iSUA), a relatively common condition with more favorable outcomes, highlighting the need for reliable differential markers. This study was performed to identify the risk factors for UAT in pregnant women. Also, we compared maternal and neonatal outcomes between UAT, iSUA, and normal controls with three umbilical vessels (NC). Patients and Methods: This retrospective study was conducted at the Women's Hospital, Zhejiang University School of Medicine. A total of 195 participants were included between January 1, 2020, and December 31, 2024, including 65 of UAT, 65 of iSUA, and 65 of NC. The baseline information, laboratory data and relevant perinatal outcomes of all participants were collected and analyzed. Logistic regression models were employed to evaluate the association between antepartum findings and UAT in pregnant women. Results: Compared with the iSUA group, the UAT group showed higher rates of abnormal fetal movement (p=0.006) and fetal heart rate (FHR) patterns (p<0.001), shorter prothrombin time (PT) (p=0.002) and lower high-density lipoprotein (HDL) levels (p=0.014). Doppler assessment demonstrated lower umbilical vascular indices in the preterm UAT participants (<37 weeks), including lower systolic/diastolic (S/D) ratios (p=0.037), pulsatility indices (PI) (p=0.005), and resistance indices (RI) (p=0.018), with two cases showing absent end-diastolic flow. Postpartum pathology revealed shorter cord length, smaller diameter, and higher hypercoiling prevalence in UAT. Multivariate analysis identified abnormal fetal movement, abnormal FHR patterns, prolonged activated partial thromboplastin time (APTT), and cord hypercoiling as the risk factors for UAT, while longer PT, higher HDL, higher umbilical vascular indices and favorable umbilical cord parameters served as the protective factors (all p<0.05). Critically, the UAT group was more likely to experience adverse maternal and neonatal outcomes than other two groups. Conclusion: This study identifies distinct clinical, laboratory data, and sonographic markers that effectively differentiate UAT from iSUA, with abnormal fetal movement and FHR patterns, prolonged APTT, and umbilical cord hypercoiling as prominent risk factors for UAT.