* Drink plenty of fluids while there (it's great your going to FL, safe for hygiene, tap water etc)
* Try to avoid the mid-day sun
* Rest as much as possible during the day
* Remember the amniotic fluid is already warmer than body temperature (hense why preg women feel so hot all the time) and that if you start overheating it's bad for LO as they can't sweat or escape the heat, so stay under sun brollys on the beach etc
* Wear flight socks while travelling
* Move around during the flight don't sit/lay still for the 7 hours
* I know it's EARLY days but pack you maternity notes in your handluggage, you just never know what might happen even a trip or fall can then be recorded properly
* Take paracetamol with you, it's not something they sell in straight format version over there and if you develop a bad headache or something you'll want to have something to hand to take without risking their more unknown brands.
* Research the nearest hospital/clinic to your hotel (with maternity unit) just incase 'anything' happens.
I'd just say though, go, have a great time, be sensible and you'll be fine I'm sure...your travelling at the best time to travel although if you will be at or over the 20 week marker on your return from FL I'd check with BA that they don't want a medical certificate (from your GP) saying your ok to fly...BA staff on the American side might have different rules to this than the UK staff so check both ends - it's nothing to carry an extra slip of paper with you if it's going to be needed. I can't remember how many weeks you are but some airlines want them from 20 weeks, others 24 and most won't let you fly after 28. Worth just checking thought.