Inoculation and vaccination certificates may be needed for your trip (your airline or travel agent will advise you accordingly). Such procedures must of course be completed in advance.
General information about inoculations and other precautions are available on the website of the Belgian Institute of Tropical Medicine .
It may also be useful for safety reasons to equip yourself with insect repellents, mosquito nets, condoms, sterile needles etc. Ask your doctor's advice.
Make sure you have an adequate supply of any prescription medication and a copy of the prescription with you. There is a pharmacy at Brussels Airport.
Airlines usually refuse to carry passengers after their 36th week of pregnancy. A medical certificate is required after the 28th week.
If you have a medical condition and any doubts about whether you should fly, ask your doctor. You may be required to advise your airline in advance of certain conditions or special assistance which may be required.