Sienna Dumas, now five, was diagnosed with central precocious puberty (CPP) at just ten months old after a health visitor noticed enlarged breast tissue. The condition causes the brain to trigger puberty signals years earlier than normal, and without treatment she would have progressed through puberty before her peers. Her mother, Sophie Dumas, is considering freezing her daughter's eggs and is concerned about the emotional impact of the condition as Sienna grows up.

Sienna receives hormone blocker injections (GnRH analogue) every four weeks to suppress puberty, with treatment expected to continue until around eleven or twelve years of age. She underwent extensive diagnostic testing including Stim tests (blood tests with synthetic hormone injection), X-rays to determine bone age, and an MRI scan—the latter of which ruled out underlying brain abnormalities. The diagnostic procedures were described as distressing, requiring blood draws from the baby's heels and the mother using various soothing techniques during hospital appointments.