British doctors have developed the first blood test for postnatal depression in a breakthrough that could ease the plight of tens of thousands of women who suffer from the condition every year, Sky News has learnt.

Doctors believe a £10 screening test they have developed – which could be administered as part of ordinary NHS antenatal checks – would allow women found to be at risk to receive treatment for the disease before they give birth.

Around 90,000 pregnant women a year – around one in seven – develop some level of depression in the first three months after giving birth.

In severe cases it can result in new mums committing suicide or harming their babies.

Professor Dimitris Grammatopoulos, who led the research at University Hospitals Coventry and Warwickshire NHS Trust, said the research was “extremely important”.

He said: “There is evidence that if you can identify women at risk early you could treat early or introduce measures to prevent or stop the process of the disease.”

The early warning should mean that simple support from families and health professionals is enough to prevent symptoms developing.

A study of 200 pregnant women, published in the current edition of the Journal of Psychiatric Research, found two molecular “signatures” in the genes that increased the risk of postnatal depression by up to five times.

Although previous research has found genetic “markers” linked to the condition, this is the first time that genetic variations have been found in the hormonal pathway that triggers it.

The researchers believe that changes in oestrogen levels during pregnancy make women more sensitive to the stress hormone cortisol.

But whereas most women “reset” the hormonal imbalance soon after their baby is born, those with the genetic variations are unable to do so, leading to postnatal depression.

Prof Grammatopoulos said he could test women for the genetic changes for between £30 and £40.

But automating the test so that robots could screen large numbers of samples would bring the cost down to just £10.

And he is looking for further genetic changes, called single nucleotide polymorphisms, to increase the predictive power of the test.

He said blood samples already taken routinely in the early stages of pregnancy could then be screened.

“Usually we focus on the mother, but the negative impact on the child is also immense,” Prof Grammatopoulos said.

Between a third and a half of women with postnatal depression develop severe symptoms.

Rachael Dobson, 24, said the new test could prevent other women suffering as she did.

She felt “useless as a mum” when her son Andreas was born three years ago.

As her sense of hopelessness grew, she considered suicide – or even harming her son.

Only when she began to consider killing him did she contact her health visitor.

She said: “I remember him crying loads and I’d tried everything in the book – feeding, winding, changing his nappy – because he would not be quiet.

“I just thought ‘What if I smothered him?’. At least he would then be quiet and I could sort myself out.

“But within a split second you are almost scared yourself because how could you think that about a vulnerable baby.”

Support from health professionals and her husband slowly improved her symptoms. But it has taken the best part of three years.

Mrs Dobson set up the Pre and Postnatal Depression Advice and Support charity (Pandas), which runs a helpline: 0843 2898401.