Does my cervix length seem concerning to you? Or anyone else experience somethin like this?

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I'm 20 weeks 6 days today. Two weeks ago I had a cervical length check when I was 18 weeks 6 days and my cervix was a 4.6 I think. And I had another check today and I was a 3.27. The mfm doctor said it doesn't concern him and that anything above 3 is normal. he said if it makes me more comfortable I can come in next week to look again instead of two weeks out. He said some doctors would say to put a stitch in but he recommends just watching and then if something were to change put in a stitch. He said my cervix is normal. Does 4.6 two weeks ago to 3.27 now seem concerning tho? I'm also on Makena/ p17 injections weekly every Monday that I get. Anyone else go through something similar?