Lordosis. Increased estrogen can cause changes to tendons which position the hip, and result in a forward tilt. This causes increased curvature in the lower spine, decreasing the overall spinal length. It is normal in most Cis women and newly half of Trans women. 5 cm seems to be the normal height loss.
There is some misinformation within the medical community conflating Lordosis with Hyper Lordosis, a condition where the hip tilt is excessive, or uneven, which can cause hip and leg pain. Hyper Lordosis is treated by physiotherapy. There are doctors who are ignorant of Lordosis, and will tell you all loss of height is due to age related disc wear, but this is something which happens over decades, not months.
My doctor measured me prior to starting HRT at 173 cm (The same as I had always been) and again after 8 months on Estrogen. I lost 3 cm in that time, and my doctor could not explain it. My endocrinologist was also at a loss, suggesting that I may have osteoporosis and bone collapse! He referred me to have a bone density scan which showed normal density.(I found a new doctor for my hormones). I learned about Lordosis from an Osteopath who rolled their eyes and said few doctors knew about it.
I undertook a solid exercise program to p[repare for my surgery, and my stronger back increased my height by 1 cm by reversing some of the Lordosis.
Hugs,
Allie