Info from my fertility dr about spotting

So I have a ultrasound every week and am high risk with a successful iui. Every time I see my dr he asks about spotting. I haven't had any but I asked why? He said spotting is a indicator of low progesterone and the most common cause of miscarriage. It causes thinning of your uterus and is the most important support in early pregnancy. If you do have low progesterone it's as easy as taking one extra pull a day. So what I'm saying is if you are spotting demand they check your progesterone. I get test every week... I hope this info helps someone