You can fly or travel during the first 12 weeks of pregnancy but it's not recommended to since you'll be feeling very sick and have nausea and vomiting etc which the flying will make worse.
It's recommended to just wait until after you're past 12 weeks of pregnancy before traveling or flying while pregnant.
When you fly or do any traveling during the first 12 weeks of pregnancy your risk of miscarriage is much higher than if you were to wait until the 12 weeks have passed.
Some people have flown safely during the first 12 weeks of pregnancy but it's not advised too.