In January 1961, Sigrid Paul gave birth to a little boy in a Berlin hospital. Her first child, it was a difficult labour and the baby was whisked away to intensive care. As she lay recovering, Sigrid had no idea that little Torsten, as she had named him, would become inextricably and cruelly caught up in cold-war politics. Eight months later, the Berlin Wall would go up, initiating, says Sigrid, “a sequence of events with consequences beyond our wildest imagination”.

It’s the 20th anniversary of the fall of the Berlin Wall on Monday. Only now does Sigrid, 75, finally feel able to tell the story of how, nearly half a century ago, she and her son were trapped in a twilight zone between communist east and capitalist west. […]

[Her infant son] Torsten was given an artificial diaphragm, oesophagus and antrum (stomach exit), and in July Sigrid was finally allowed to take him home to East Berlin. He was still fragile and needed medicine and special food, both only available in the west. Every Monday, Sigrid would travel across the city to pick up Torsten’s life-saving package.

Then, on 12 August, everything changed. At midnight, the police and units of the East German army were given orders to close the border. Barbed-wire entanglements were rolled out and the building of the Wall began. By the time Sigrid woke on the 13th, the route from east to west was closed. She applied for a permit to the west to obtain Torsten’s food and medicine but was refused. “Our baby food is good enough,” was the reply from the German Democratic Republic (GDR) health ministry.

Within days, Torsten started coughing up blood and Sigrid took him back to the Charité hospital in east Berlin. There, a doctor named Schneeweiss did everything he could. He pumped Torsten’s stomach, but he got sicker and his temperature got higher. Sigrid was beside herself. In the early hours of the morning, Schneeweiss sent her home. “Years later, Dr Schneeweiss told me what happened,” says Sigrid. “He realised that neither he nor any other doctor at the Charité could help. The only doctors who could help were on the other side of the Berlin Wall.”

Transferring patients across the Wall was now forbidden, with one exception – heart cases. Schneeweiss knew Torsten could die if he stayed in the east. He confided in another doctor and together they falsified Torsten’s papers and listed him as a heart patient. Schneeweiss had sent Sigrid home so he could illegally spirit her baby to the other side of the Wall. “That was the moment Hartmut and I were separated from our sick child,” says Sigrid. “Torsten’s life was saved by a piece of benevolent deception schemed up by two doctors.” The decision was to shape the rest of their lives.