Genetics May Mean Some Women Don't Need Pain Relief During Labor

Some women may not need pain relief while giving birth thanks to their genetics, according to a study.

Researchers who published their findings in the journal Cell Reports recruited 158 women from the U.K. who said they did not need pain relief when giving birth to their first child vaginally. Women were excluded from the study if they had any major diseases or underlying conditions known to affect pain.

The participants provided a sample of their blood or saliva, from which the researchers extracted their DNA. By studying the women's DNA, the researchers found they shared a variant of the gene KCNG4.

Of those women, 39 agreed to have thinking and pain threshold tests. The team matched them with 33 women who gave birth to their first child at the same hospital, but who did need pain medicine, and acted as the control group. There was no significant difference in the weight or head circumference of the women's babies.

The participants answered questions to help the researchers see if they held certain beliefs that might affect their pain threshold. Next, the researchers tested their pain thresholds to cold, heat and pressure using arm cuffs. The team found a "very striking" difference in the pressure threshold in the test group, which they believed may be down to their genetics.

Next, the researchers tried to corroborate their findings in mice whose sensory nerves were made to produce the genetic variant the women shared. As expected, the mice needed more stimulus to fire an electrical signal linked to sensing pain, which the team believed came down to the genetic variant.

Co-author Ewan St. John Smith of the Department of Pharmacology at the University of Cambridge said in a statement: "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."

Smith told Newsweek the gene they studied had not been fully explored in the context of pain until now.

The team was inspired to carry out the research as a means to gain a better understanding of pain more generally, he said. Chronic pain affects millions of people, and the drugs patients currently take do not always work, either not giving adequate pain relief or because they have serious side effects.

"By understanding more about the genes that regulate pain, there is a potential opportunity to identify new targets for pain treatment and thus to increase the possibility of developing new drugs," he said.

Smith said it remains unclear whether the pain in the mice would have changed if the gene were blocked, and more research is needed to show whether treatments could be designed that target the gene for pain relief.

As the gene is produced by many different nerve cells in the body, "it might be difficult to develop a treatment that affects pain-sensing nerves without producing side effects as a result of affecting nerves in [the] brain," he said.

Smith said: "Fundamentally, this study identifies a gene involved in pain sensation, but pain is complex and many many genes are involved in controlling pain perception, whether or not this gene can truly be targeted for treating pain, without causing unwanted side effects, remains to be determined."

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A stock image shows a woman just having given birth. Researchers have investigated why some women don't need pain relief during pregnancy. Getty