Butterfly, you're going to hear different experiences from different perspectives with HRT, so here's my take on it.
I had quite a lot of breakthrough bleeding after starting HRT. In my case, 100mg Uterogestan wasn't enough to prevent it.
Initially I was prescribed Estrogel x2 per day with 100mg x1 Uterogestan, and I had some breakthrough bleeding. After blood tests, my Estrogel was increased to 3x per day to bring my oestrogen levels up to the optimum for treating osteoporosis, which was previously diagnosed. I had even more breakthrough bleeding on this higher dose.
My consultant recommended a Mirena instead of the Utrogestan as a better option to control the bleeding, so I did that. It took 5-6 months for the bleeding to settle down. I was told it was normal and that it takes time for the body to get used to the Mirena. After that happened, the bleeding more or less stopped, apart from very rare spotting.
However.... I was having troublesome night sweats so my consultant suggested 4x Estrogel daily, and although there was a tiny bit of spotting a couple of times, the Mirena seemed to be keeping it all under control. But then one day.... I had a bleed. So I rang the clinic and they arranged another scan. I had some thickening of the endometrium so I had a biopsy there and then. My consultant thought that the scan was otherwise OK and recommended that I add 100mg Uterogestan to my HRT regime. This is with the Mirena still in place.
I have to stress that I've had quite a few scans because of the bleeding in the past 3 years or so that I've been on HRT. The biopsy appeared to be OK.
You need sufficient progesterone on continuous combined HRT. If you are post menopausal, my consultant says there should be no bleeding and that cyclical HRT can potentially mask other conditions because of the scheduled bleeding. He didn't rule it out if that was what I wanted but he didn't recommend it. I take a higher dose of Estrogel because firstly, my oestrogen levels need to meet the optimum threshold for osteoporosis, and for symptom control. Not everyone needs to be on this high a dose. Secondly, even on 2x pumps of Estrogel daily, 100mg Utrogestan wasn't enough to prevent bleeding.
My advice — report any bleeding to whoever is prescribing your HRT. An ultrasound scan is only reliable for 6 months. If you are bleeding and haven't had a scan in the past 6 months, you need one to rule out any other causes of bleeding. If everything is fine, you need to consider either a Mirena OR increasing your Uterogestan to 200mg.
Everyone has different experiences though. There's no ‘one size fits all' with HRT. But you really should have any bleeding checked out.