What is: a Trimester?

If you are a pregnant mother or involved father and sign up for classes at the PHI Center in anticipation of your baby’s birth, we’ll put you a class based on your trimester. We offer classes for first, second or third trimester parents so you’ll learn specifically about what’s happening in your pregnancy. If you’ve been seeing a doctor you’ve probably heard the word “trimester” spoken dozens of times, but do you know what it means? Do you know how we got that term and why we use it? Let’s learn together.

The American school system made popular the word semester. Most schools divide their academic year into two “semesters,” but how does that help us understand a trimester? The answer’s found in the etymology of the word.

Technically, semester is a German word derived from its older Latin cousin “semestris.” That word comes from two smaller Latin words, “sex” which means six, and “mensis” which means month. In the German school system Semester is used literally; they have two six-month semesters. In America the semester doesn’t represent six months, instead it represents dividing one period of time into two equal parts (The academic semester is closer to four months). For a pregnancy it’s a little simpler, trimester comes from two words as well: “tri” meaning three, and “mensis” meaning month. Trimester literally means three months. As an aside, the term menstrual also comes from this Latin word “mensis,” and simply refers to a monthly cycle. Your pregnancy is divided into three, roughly three-month periods called trimesters.

The key to understanding trimesters and your due date is accepting it’s not an exact science. The 280 day (forty week) gestation period is derived from an average. The due date of a baby has a give or take of up to two weeks based on when conception happened. And we can’t forget some months have five weeks while others have four. At the Phi Center, we’ll utilize your last menstrual period (LMP) to estimate your due date and calculate which trimester you’re in.

We offer first trimester classes up to the twelfth or thirteenth week of your pregnancy, second trimester classes until your about twenty-six weeks, and third trimester classes up till your baby is born. If the first day of your LMP was January 1st you would enter your second trimester around March 25th, enter your third trimester about the first of July, and possibly deliver on October seventh. But remember the key, these dates are estimates not exacts. You might deliver at the end of September or the middle of October, but that’s okay. And you’ll be okay, just listen to your doctor and enjoy the process.

So a trimester is roughly one third of your pregnancy. The exact day you grow from one trimester to another varies depending on when the little life you’re expecting began.

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