Umbilical cord velamentous insertion vasa previa true knot nuchal cord abdominal insertion sigle umbilical artery umbilical vein cord mass etc ;

脐带：帆样附着，前位血管，脐带 真 结，颈部脐带，腹部脐带附着，单只脐动脉，脐静脉，脐带肿块等；

Obstetrical Risk Factors and Pregnancy Outcome of Fetuses with True Knot of the Umbilical Cord

脐带 真 结的产科因素及妊娠结局

True knot and torsion of cord are cause by occasional factors and difficult to prevent .

脐带异常中脐带 真 结节、扭转均属偶然因素，难以预防。