PNDDoctors have developed the first blood test for postnatal depression (PND) in a breakthrough that could see tens of thousands women at risk receive treatment for the condition before they give birth.

Researchers from University Hospitals Coventry and Warwickshire NHS Trust have described the discovery as "extremely important". They believe a screening test based on their findings could be administered as part of ordinary NHS antenatal checks.

Introduce methods to stop the disease
Every year, about one in seven pregnant women 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. But having an effective early warning system could allow simple support from families and health professionals before symptoms develop.

Study lead Professor Dimitris Grammatopoulos 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."

Increased risk of PND
The study of 200 pregnant women, published in 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.

Though 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.

Enhanced predictive powers
Professor Grammatopoulos said he could initially 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.

If the test is enhanced to identify further genetic changes, called single nucleotide polymorphisms, its predictive power would become even greater. Professor Grammatopoulos also suggested 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," he added.