Can estrogen patches strengthen bones in women with CF?

This study looks at how estrogen and other hormones affect bone development in teenage and young adult women with cystic fibrosis (CF). It has two parts: an observational study that tracks bone health in women using different types of birth control, and a small feasibility study where participants use estrogen skin patches for a year. Researchers will measure bone density, blood markers, and quality of life to see if estrogen therapy is helpful and practical for this group.