Just googled and found this:
"Flying in early pregnancy is safe. However, during the first trimester, the main concern over flying is making your pregnancy symptoms, like morning sickness, worse. (You may want to make sure you have a extra few sick bags nearby, just in case.) And a mildly stuffed-up nose on the ground could become much worse once you’re in the air."
(https://www.pregnancy-info.net/wellbeing_flying.html)