The Bridget Jones and Miranda star, 46, who has three sons with husband Andrew Bermejo, also hit back about the pressure facing mums of Down's Syndrome babies to abort their children.
Sally had been speaking to families who had been advised to have a termination as part of a new BBC2 documentary, and said she was 'horrified' to hear the suggestions many of the expectant parents had received.
'I have heard many stories of women being pressurised by medical professionals to screen, and even to terminate,' Sally wrote in the Radio Times.
One of the mothers featured on the show told Sally that a medic said to her: 'Let's stop this nonsense now while you still can', whilst another was booked in for an abortion without her consent.
Another was told: 'Your marriage will break-up if you have this baby.'
The documentary, titled 'A World Without Down’s Syndrome?', is centred on the news that a new screening test is said to be able to detect Down’s Syndrome in pregnancies with 99 percent accuracy - leaving Sally to explore the prospect of a world where people choose not to have children with the condition.
Sally is mum to three boys, Oliver, Luke and Tom
Sally was shocked to discover it is still legal in the UK for a baby with a disability to be terminated right up until the moment when labour starts, and heartbroken by the fact that in the Netherlands, disabled babies in the Netherlands can be given a lethal injection after birth.
'I don't understand how that can be acceptable, but I do know that it hurts my heart,' she said.
'If we deny someone the chance to be born because we've decided they won't meet some predetermined measure of status or achievement, then we've failed to grasp what it means to be human.'
Explaining her reaction when her eldest son Oliver, now 12, was diagnosed with Down's Syndrome shortly after his birth, Sally said: 'I hyperventilated and flapped my arms.'
'Once we got over the initial shock, we just got on with it. It was never going to be easy, but we never moaned about the hard times'.
'Although Olly was the reason I started making this film, you'll be relieved to hear it's not just about him. It’s not just about Down’s Syndrome either. It's a film that asks what kind of society we want to live in and who should be allowed to live in it.'