So clearly in the first trimester. I live on the east coast and had a business trip on the west coast so I POAS before I left (even though I was 7dp6dt or 13 dpo on my FET). My best was not scheduled until 14 dpt -- even though I transferred Day 6 blasts my clinic does betas at 14 dpt. Anyway, BFP before getting on the plane and I was fine. I was going to fly a bunch between 18 and 30 weeks preggo but right before a trip to London I came down with pregnancy induced hypertension which put ALL travel (not just plane) out of it for me. If not for that, my OB would have been fine with me flying.