This is a very common problem for both HCPs and patients.
It is not unusual to have some unexpected (unscheduled) bleeding in the first 3 to 6 months after starting HRT, even if your last natural period was many years ago. Every woman should be reviewed after the first 3 months on HRT and if the bleeding shows no signs of improving, the HRT can be adjusted to try to settle it. Again, bleeding is not unusual when changing the dose or type of HRT. Any bleeding that persists after 6 months on HRT, or starts once the patient has been on HRT for over 6 months, does need to be investigated. Very heavy or painful bleeding, post-coital bleeding or bleeding associated with other worrying symptoms would need to be investigated sooner.
Some women will just need a pelvic ultrasound scan, others may need a hysteroscopy and biopsy. Unfortunately, there are currently no national guidelines on cut off points for endometrial thickness seen on ultrasound scan to help decide on who needs to be referred. Gynaecology departments receive many advice and guidance requests about this. For now, HCPs still need to refer these patients to gynaecology services but I hope to liaise with our local hospitals to design a management protocol for this at some point.
Most of this unscheduled bleeding is due to the HRT but it is important to exclude endometrial polyps or other pathology such as endometrial hyperplasia or endometrial cancer. Risk factors for endometrial cancer include obesity, PCOS and Type 2 diabetes and it is the 4th most common cancer in women in the UK. Women on continuous combined HRT have a lower risk of endometrial cancer than women not on HRT.