Trimester
A trimester was a period of three months in one's pregnancy. Pregnancies could have as many as three trimesters. () Morning sickness usually ended after the first trimester in Humans. ()

Eleven hours after his 2365 "conception", Deanna Troi's baby was already halfway through the first trimester in terms of development. ()

In 2378, The Doctor, having temporarily taken on the appearance of B'Elanna Torres, called Tom Paris "sweetheart", causing Paris to pronounce that Torres was getting affectionate in her third trimester.  ()

External link

Medical measurements
Time measurements