What Does the Umbilical Cord Do?

Umbilical cord

The umbilical cord connects your baby’s stomach to the placenta which is in turn indirectly connected to your blood supply and measures around 20 inches long at birth. The main function of the umbilical cord is to provide nutrients and oxygen from the placenta to the baby and to return the blood without oxygen and waste products, such as carbon dioxide, from the baby back to the placenta. Towards the end of the pregnancy, the umbilical cord also transfers antibodies from the mother’s placenta to the baby. This transfer of antibodies means that your baby has immunity to infections for about three months after being born.

The umbilical cord is made up of:

  • Two arteries that return the waste products
  • One vein which is usually larger than the two arteries that provides the nutrients and oxygen
  • A sticky gelatinous substance that envelops the arteries and vein called Wharton’s jelly
  • A membrane called the amnion that covers the Wharton’s jelly


The umbilical cord is developed from and contains remnants of the yolk sac and is also derived from a structure called the allantois, a sac-like structure appearing in early embryo development. It forms by the fifth week of gestation and is approximately equal in length to the crown-rump length of the fetus during the entire pregnancy.

What happens to the umbilical cord at birth and following birth?

Once you have given birth to the placenta, the cord can be cut. This can occur anywhere between a few seconds to a few days afterwards, although the latter, termed “lotus birth“, is not recommended. Although in lotus births the cord will eventually dry up and fall off 3–10 days after birth, there is an increased risk of infection from the still-attached placenta in the period beforehand. Bacteria from the placenta are able to able to enter the baby’s body via the umbilical vein and this could be very harmful for your baby. However there is some evidence supporting leaving the umbilical cord attached for at least 30 to 60 seconds, termed delayed cord clamping, particularly in babies who are preterm.

Usually, the midwife or doctor will clamp the cord about 1.5–2 inches from your baby’s belly button with a plastic clip and will also place another clip at the end of the cord nearest the placenta. The cord is then cut leaving a stump of about 1–1.5 inches that will dry out and drop off between 5–15 days following birth. It usually takes a further 7 – 10 days for the belly button to heal completely. Until this occurs, you should make sure that the belly button area is clean and dry to prevent infections. If you notice any discharge or bleeding from your baby’s belly button, if the base appears swollen and red or if the cord seems painful to your baby, contact your midwife or doctor for advice.

Melody Watson
Melody Watson holds Bachelors degrees in Biochemistry and Microbiology. She works as a medical writer for a medical communications agency in Berlin, Germany, where her work ranges from medical translation to writing publications for medical journals. Melody is passionate about promoting science, including evidence-based medicine, and debunking pseudoscience.

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