Some women don’t need an epidural during childbirth, while childbirth is more painful for many women.
Now researchers at the University of Cambridge found a genetic clue which explains why some women have a natural epidural and others don’t have.
A collaboration between clinicians and scientists based at Addenbrooke’s Hospital, part of Cambridge University Hospitals NHS Foundation Trust (CUH), and the University of Cambridge sought to investigate why some mothers report less pain during labour.
Scientists put a group of women, all of whom gave birth without requesting pain relief, through a number of exercises to test their resistance to discomfort, including applying heat and pressure to their arms and asking them to plunge their hands into icy water.
When compared to another group of mothers who did require pain relief, they were shown to have a far higher threshold before they experienced pain.
“It is unusual for women to not request gas and air, or epidural for pain relief during labor, particularly when delivering for the first time,” said Dr. Michael Lee, joint lead author, in a press release.
Next, senior co-author, Professor Geoff Woods, and his colleagues at the Cambridge Institute for Medical Research sequenced the genetic code of both groups of women and found that those in the test group had a higher-than-expected prevalence of a rare variant of the gene KCNG4. It’s estimated that one approximately 1 in 100 women carry this variant.
KCNG4 provides the code for the production of a protein that forms part of a ‘gate’, controlling the electric signal that flows along our nerve cells. As the joint first author Dr. Van Lu showed, sensitivity of this gatekeeper to electric signals that had the ability to open the gate and turn nerves on was reduced by the rare variant.
This was confirmed in a study involving mice led by Dr. Ewan St. John Smith from the Department of Pharmacology, who showed that the threshold at which the ‘defective’ gates open, and hence the nerve cell switches ‘on’, is higher—which may explain why women with this rare gene variant experience less pain during childbirth.
Dr. St. John Smith, senior co-author, explained: “The genetic variant that we found in women who feel less pain during childbirth leads to a ‘defect’ in the formation of the switch on the nerve cells. In fact, this defect acts like a natural epidural. It means it takes a much greater signal—in other words, stronger contractions during labour—to switch it on. This makes it less likely that pain signals can reach the brain.”
“When we tested these women, it was clear their pain threshold was generally much higher than it was for other women,” said Lee, a lecturer with the University of Cambridge’s division of anaesthesia.