Research into miscarriage and developmental abnormalities is being hampered by an outdated rule on keeping embryos for just 14 days, an ethicist has argued.

Scientists have been calling for several years for a change to the law which says human embryos can only be kept for 14 days for experiments, with many wishing to extend this to 28 days.

Writing in the Journal of Medical Ethics, Sophia McCully, from King’s College London, said experts are unable to study embryos for a range of conditions due to the fact that some parts of the embryo have not developed by day 14.

“We can take the development of the heart as an example of the knowledge we are missing,” she said.

“The heart is the first organ to develop, beginning from around 16 days and forming a functional beating structure, although one that is still immature, by day 28.

“Congenital heart disease (CHD) is a problem caused by abnormal formation of the heart that occurs while the foetus is still developing.

“In the UK, CHD is one of the most common birth defects, affecting around eight in 1,000 babies.”

She said other common birth defects that cannot currently be explored include problems with the neural tube, which is formed between day 18 and 30.

“Neural tube defects are those where this process malfunctions, leaving an opening in the spinal cord or brain,” she said.

“This will lead to problems such as spina bifida or severe brain abnormalities.”

Ms McCully argued that extending the time limit to 28 days will lead to a greater understanding of congenital defects “as well as to potentially improve in vitro fertilisation (IVF) and reduce rates of miscarriage.”

She added: “It would also allow better testing of the safety of new techniques, such as mitochondrial replacement therapy (MRT, where defective mitochondrial DNA is replaced with that of a donor).”

There are a multiplicity of reasons why embryo research beyond 14 days can help us realise the metamorphic potential of healthcare

Scientists have said the 14-day rule, endorsed in 1984, does not take account of newer medical advances.

Ms McCully said it is now safe and timely to make a policy change and extend the rule without fear of any “moral and regulatory slippery slope”.

Furthermore, she argued that selective abortion has increased but, by using research to correct problems in the foetus, the frequency of abortion may reduce.

“The 14-day rule has become limiting, and just because something has once worked does not mean it should stay the same or not strive to improve,” she said.

“As is clear to see, there are a multiplicity of reasons why embryo research beyond 14 days can help us realise the metamorphic potential of healthcare.”