Rapid method for the measurement of foetal scalp blood pH

Foetal blood pH is a key diagnostic of foetal hypoxia and is used to determine if expedited delivery is required. Failure to deliver the baby in a timely manner can lead to neonatal brain damage.

Currently foetal health in the womb is assessed by a combination of foetal heart monitoring, and if found to be abnormal, by obtaining a foetal scalp blood pH measurement. The acquisition of foetal scalp blood for pH is technically difficult and takes time to perform (around 15 minutes), a significant issue if the baby is believed to be compromised. Oxford researchers have developed a bespoke sensor that will revolutionise foetal assessment at point of care.

In the US and EU, 9 million babies are born each year. 50% of the babies born will be subject to continuous electronic foetal heart monitoring and have the potential to require foetal scalp blood pH monitoring.. Failure to assess foetal status by performing foetal scalp blood pH or a delay in obtaining foetal scalp blood pH is a major case of litigation. In the last NHS litigation report, maternity accounted for over half the litigation budget, £700m out of a total budget of £1.68m.

An abnormal pH measured in foetal scalp blood is indicative of foetal distress. Foetal distress is any condition in which a fetus is endangered, struggling or unwell, which is typically characterised by the fetus not having an adequate oxygen supply. If foetal distress is not corrected in a timely manner, this can cause irreversible harm to the fetus, such as neo-natal brain damage. Blood pH measurements can therefore be used to determine whether any medical intervention, such as a Caesarean section, is required.

Foetal scalp blood pH measurements currently used suffer from a large number of false negatives and measurement failures often resulting in unnecessary and potentially harmful medical intervention, such as Caesarian section. Caesarean sections involve much greater risks compared to natural birth, such as an increased risk of surgical injury to both the mother and child. Even without major complications, caesarean section typically involves more blood loss, an increased risk of infection, and an increased risk of uterine rupture in further pregnancies.
As the process of obtaining foetal scalp pH is technically difficult, it is something that many clinicians avoid. Making the process significantly easier will encourage its use.

Scientists at Oxford have developed a method of reliably and accurately measuring foetal blood pH and giving a measure of the quality of the result. The method, with partners, is suitable for translation into a practical sensor with many advantages over the current technologies. The quality of pH measurement is a novel and generic feature. This bespoke sensor would make the process of obtaining foetal scalp blood easier, be able to be performed at smaller cervical dilation, by midwives or doctors and give a much faster result. This would, in turn, lead to increased use of pH measurement and reduced adverse perinatal outcomes by allowing more timely delivery of at risk babies.

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