The development, structure and blood flow within the umbilical cord with particular reference to the venous system

The umbilical cord is a helical and tubular blood conduit connecting the foetus to the placenta. The umbilical cord achieves its final form by the 12th week of gestation and normally contains two arteries and a single vein, all embedded in Wharton's jelly. The structure of the umbilical cord receives only a cursory glance during many obstetric ultrasound examinations: with imaging limited to documenting the number of vessels within the cord and the insertion sites at the foetus and placenta. Extensive research into blood flow characteristics of the umbilical cord arteries has been undertaken and is now widely applied in contemporary ultrasound practice. In contrast, investigation of umbilical vein blood flow is only instigated in instances of foetal compromise when the spectral waveform of the ductus venosus and pulsations in the vein are scrutinised. The current level of ultrasound imaging of the umbilical vein demonstrates a lack of appreciation and knowledge about a structure that is crucial to sustaining foetal life. The goal of this review is to increase awareness of the importance of the umbilical cord. In addition, this review will provide an information platform for undertaking and critically analysing research into the umbilical cord by providing a summary of cord embryology, structure, foetal venous circulation and mechanisms of blood flow within the umbilical cord vein.