Dozens of transgender teenagers are freezing their sperm or preserving their eggs on the NHS so that they can have babies after changing sex, The Mail on Sunday can reveal. Adolescent boys – some as young as 12 – who believe they are female are having their sperm frozen before receiving powerful hormone treatment that halts the onset of puberty and shuts down their reproductive system. They then have the option to use the frozen sperm so that they can father their own biological children after having sex-change surgery.