Sarah and Adam Campbell's son, Ewan, was delivered by Caesarean, apparently healthy and a good weight.
"The doctors said they needed to take him to the special care baby unit only because he'd been born early," Sarah, 34, a teacher from Kempston, Bedfordshire, said.
"We thought we had all the time in the world for cuddles."
Shortly afterwards, a nurse told Sarah that Ewan was having problems breathing.
"I was desperate to see my son but, because of the Caesarean, I couldn't stand or even sit in a wheelchair, so they wheeled my hospital bed to the special care baby unit.
"The paediatric consultant uttered the words no parent wants to hear: 'There's nothing more we can do for him'.
"I couldn't even see my son's face, just his blue woollen hat.
It's hard to put into words the pain we felt at losing our first child without ever having experienced the joy of getting to know him. It was like someone ripping out our hearts.
A third of women carry the bacterium, which is largely harmless to adults. It's thought it may be contracted through eating beef or fish, though skin-to-skin transmission is more likely.
However, because of their immature immune systems, the bug's effect on babies can be devastating. One in 300 exposed to it will develop the infection.
Spotting it early and treatment with antibiotics during labour or in the first few hours after childbirth can be life-saving and yet every year the infection kills 30 newborns. Another 200 are left with disabilities, including cerebral palsy and blindness.
These tragedies could be avoided, says Professor Philip Steer, an obstetrician at the Chelsea & Westminster Hospital, London.
"For their sake, I think all mothers-to-be should be given a screening swab in the latter weeks of pregnancy, then they can decide whether to have antibiotics during labour," he told the newspaper.
At present, the current NHS test picks up around half of carriers; but a new Enriched Culture Medium (ECM) test has a 90 per cent accuracy rate, says Jane Plumb, of charity Group B Strep Support.
But at present, the ECM test is only available privately for £35 - it's estimated it would cost the NHS just £10.63 per pregnant woman.
"Since introducing national screening with these more sensitive tests, the U.S., Australia, France and Spain have seen an average 80 per cent fall in the number of newborns contracting group B strep," said Jane Plumb.
"What further evidence does our Government need that a national screening programme here would save babies from death and disability?"
After discovering it was group B strep that killed her son, Sarah said: "At first, I felt relieved to discover it was this, rather than a genetic condition.
"At least it would be preventable if we had another baby. But that was quickly followed by fury - a simple dose of antibiotics would have saved my son's life."
The couple have since had two healthy babies with no complications following close monitoring. But Sarah is determined to prevent there being more tragedies like hers.
"For a long time I blamed myself for what happened to Ewan because he picked up the infection from me,'" she said.
"People tried to reassure me it wasn't my fault - there was no reason for me to know I had group B strep.
"We'll do all we can to raise awareness of this condition and continue lobbying MPs until a national screening programme is introduced. That way our son s death won't have been in vain."