Jesy Nelson has opened up about the “bittersweet” feeling of achieving the historic change to test babies for a devastating muscle wasting disease.The former Little Mix singer revealed her twins’ future is uncertain as medics still assess how much of their muscles died off before they were diagnosed late and then treated. Jesy had lobbied the government and joined with the Mirror to campaign to have all newborns tested for spinal muscular atrophy (SMA) after twin girls Ocean and Story were diagnosed too late after irreversible nerve damage. She has been told they will likely never walk.Jesy spoke to the Mirror moments after the government agreed to screen all newborns in England for SMA in one of the final acts of Sir Keir Starmer’s government.‌Jesy, 35, said: “It's just amazing and it's also a bit of a bittersweet feeling at the same time. It's hard because I don't want this to sound like I'm not grateful and happy about it.“What has just happened is amazing but it's just sad that it also took for my story to get it to this place, to give it this push to get it over the line. If this had been taken seriously a few years ago, maybe my girls wouldn't be in this situation.”‌Around 50 children a year are born with SMA which is caused by a faulty version of the SMN1 gene. It does not stimulate the production of a key protein that maintains the health of the nerve cells that transmit signals between the brain, spinal cord and muscles.Without this protein these nerve cells - called motor neurons - die off and so the muscles particularly in the legs, chest and arms don't get the message to move and waste away. Babies with the more severe Type 1 form that Ocean and Story have can end up needing a machine to breathe at night and being fed via a tube directly into their stomach.Jesy said the twins are tested every three months at London’s Great Ormond Street Hospital to assess what remaining motor neurons were left and could be saved since they started treatment. She said: “I'll be honest with you, it's not, it's not been great with the girls. They have a three-month test… and their numbers went down.‌"If there's no progress then they may have to go back on treatment so it's quite a scary time for me at the moment. The treatment is super new as well.”Ocean and Story were diagnosed late at six months old, despite repeated visits to the GP and healthcare visitors checking in on them. They were initially given the breakthrough gene therapy Zolgensma - a one-off infusion that carries a healthy copy of the SMN1 gene to the brain and nerve cells where it starts delivering the missing SMN protein. This is effectively a cure if given soon after birth.The twins may need to take another drug called Evrysdi daily to continue to increase the production of the SMN protein and give them the best possible life. Jesy explained: “[Zolgesma] is still life-changing and obviously it saves their life, you know. It stops them from bloody dying. But if they'd have got that from birth, then it would have been a whole different ball game.‌“If you get it later on in life it's uncertain what the treatment will do. Not every baby is the same. Lots of babies have had positive outcomes, even if it's later, but not all do.”She added: “If you don't get that treatment from birth you don't know what muscles are dead and what can be saved. And unfortunately that is the problem with my girls at the moment. We don't know what is still working and what isn't and it's all just a bit of a guessing game at the moment… I'm just trying to be hopeful, but it's tough. It's really tough.”‌Jesy has been followed by cameras for the new Prime Video documentary Jesy Nelson: Life Changing, which is released on Friday. The landmark decision on SMA screening means that from October some two thirds of babies in England will be tested and this will be expanded to all newborns from October 2027.Jesy said: “To be honest, I feel like I haven't properly taken it in. It's just mad because I remember when I first got their diagnosis, obviously I was heartbroken, and I just knew that I wanted to make the best out of it in any way I could.“I wanted to try and get this so they know when they're older, that their story was a part of change. That's going to be their little superpower. I want them to feel empowered and I want them to know how special they are and that this doesn't define them. I just feel so overwhelmed and proud that when they're old enough to understand, I can explain that to them.”‌She added: “It's just amazing to know that from October [SMA] children are going to look so different.”The Mirror has been reporting on the SMA testing scandal since 2021 and launched a campaign with Jesy calling for screening earlier this year. Jesy said: “It's an overwhelming feeling I can't really explain, to be honest. I just feel quite emotional. And I'm so grateful to the Mirror. When you go to your petrol garage, people that may not follow me on Instagram but they'll see the newspaper… and it's bringing so much awareness.”Aoife Regan, director at Great Ormond Street Hospital Charity, said: "We warmly welcome this announcement. At Great Ormond Street Hospital, teams provide specialist and wraparound care for children with SMA and their families following what is often a devastating diagnosis.”