With IUI, the sperm still need to travel through the tube to meet the egg and then the fertilised egg needs to travel back through the tube to reach the uterus. If you've got blockages or scarring that makes a successful IUI or
pg far less likely. And an IUI typically has a lower chance of success to begin with (we were told 15-20% for a
perfect IUI, vs 50% for IVF). With IVF, the tubes are out of the picture completely as the eggs are removed by the FS and the embryo is placed directly in the uterus.
If it were me, I'd go straight to IVF. But I think that's a lot easier to say after you've already done one (or three in my case) and it seems less scary.