Umbilical cord blood: understanding this vital test for vulnerable newborns

Posted: 26/03/2025

A lack of oxygen before or during a baby’s birth can have devastating long-term consequences. One of the most accurate ways to establish whether a newborn baby has been deprived of oxygen is to test the acid levels of the blood in the umbilical cord. This is of vital importance if problems are suspected during the pregnancy or birth.

There are several reasons why a baby might be deprived of oxygen in the womb. As clinical negligence specialists, some of the most common causes we see are:

• placental abruption – this occurs when the placenta detaches from the wall of the uterus, either partially or fully, which decreases the blood flow and oxygen reaching the baby;
• umbilical cord problems – issues like umbilical cord prolapse (where the cord slips into the birth canal before the baby), or umbilical cord compression can restrict the flow of oxygen. Another problem is a nuchal cord, where the umbilical cord is wrapped around the baby's neck;
• maternal health issues – conditions such as preeclampsia and eclampsia can affect the mother's blood flow and oxygen delivery to the baby. Excessive bleeding or maternal shock can also lead to oxygen deprivation;
• prolonged or difficult labour – complications during labour, such as shoulder dystocia (where one or both of the baby's shoulders get stuck during delivery), can impede oxygen flow.

Exposure to cigarette smoke, recreational drugs, or certain medications can also reduce the amount of oxygen the baby receives.

If a baby is deprived of oxygen before it is born, its body starts to produce more carbon dioxide as a waste product, and this builds up in the blood. Carbon dioxide is a weak acid, and when it dissolves in the blood, it forms carbonic acid. This increase in carbonic acid lowers the pH of the blood, making it more acidic. If the oxygen deprivation is severe, the blood can become dangerously acidic.

Oxygen deprivation at birth can have fatal consequences. An article from the BBC earlier this month outlined the tragic deaths of three babies in Scotland, which were deemed to have been preventable had their mother’s care during pregnancy and labour been better. If babies who suffer serious oxygen deprivation do survive, they may suffer from long-term health problems.

A recent study in Sweden, reported here, looked into the link between pH levels of umbilical cord blood and long-term health outcomes for babies. pH levels measure how acidic or alkaline a substance is, on a scale from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline. For human blood, the ideal pH range is slightly alkaline, typically between 7.35 and 7.45.

The study examined umbilical cord blood pH levels from births at Skåne University Hospital in Sweden, between 1997 and 2012. Researchers found that babies with a pH level below 7.05 had a higher risk of death, cerebral palsy, and epilepsy. A pH below 6.95 was associated with increased risks of cerebral palsy, epilepsy, and intellectual disability.

If the cord blood is tested, babies can be considered for treatment that may reduce the effects of their injury more quickly, such as controlled cooling, which is discussed further in our previous article here.

We regularly work with families who have lost a baby or who have a child with long-term disabilities as a result of problems around their birth. The medical experts we instruct as part of our investigations will often consider the pH level of the baby’s cord blood as a crucial indicator of whether their injury was caused by birth-related issues rather than, for example, genetic ones. This measurement can be more reliable than MRI or ultrasound imaging of the brain in determining the cause of a baby's injury, as more subtle brain injuries are not always apparent on such imaging.

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