Hi Laura,
A thin lining can be quite common, especially after an IVF cycle. You might find that in a frozen cycle, your endometrium responds better as you are not taking the IVF stimulation medication this time round. People often focus on having a very thick lining but there are other things we look for that include a good blood supply to the lining and the look of the lining – we want to see a triple line ideally and that can be achieved even if the lining is less than 8mm (which is often the measurement a clinic will want to see before doing a transfer). Some clinics may also suggest adding in some Vitamin E as this may support the womb lining – but this is something you should discuss with your clinic first before taking.
I have seen pregnancies with a lining of 6mm but good blood supply and appearance on ultrasound – so there are a lot of things we look for when we are planning your transfer.
Hope that helps,
Fran