How Long is a Trimester of Pregnancy?

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A typical pregnancy lasts 40 weeks but can normally range between 38 and 42 weeks. The countdown starts on the first day of your last period—before you’re even pregnant(!)—something I’ve always found interesting. Pregnancies are broken down into trimesters. There are three trimesters in pregnancy. Each trimester is about three months, or 12 to 14 weeks, long.

First Trimester

As stated above, the first trimester begins on the first day of your last period and lasts until about the 12th week. During that time, your body goes through tremendous changes. Hormones begin to surge in preparation of the long haul ahead. You may begin to feel tired—really tired.

I remember knowing right away that I was pregnant. We had done IVF and just had two embryos implanted the week before. It was my stepdaughter’s birthday and we decided to take a walk to a historic mansion nearby. It was a beautiful day and the mansion (complete with indoor pool) and grounds were impressive and beautiful. But on the walk back, I felt like I just wouldn’t be able to make it. Each step felt like I was putting every single last bit of my effort into it. The sun seemed hotter than hot and more golden than ever. I had my husband walk behind me with his hands on my lower back to help push me forward until we made it all the way back home.

I looked back into my pregnancy journal to see if I could share any other details of that first trimester, but I didn’t do much writing then. After that initial tiredness, I had other telltale signs of being in my first trimester. I had a twin pregnancy, so my Beta-HCG levels were quite high. It’s thought that the higher your HCG level, the more likely you are to have intermittent nausea and vomiting (aka morning sickness). Oh boy, did I have morning sickness! Mine would more accurately be termed ‘all-day, all-night’ sickness. Needless to say, my first trimester was not enjoyable.

Other changes you may go through during your first trimester include: gaining or losing weight (I actually lost weight), breast swelling and tenderness, food cravings or aversions (I couldn’t stand the smell of pizza), mood swings, digestive issues, and frequent need to urinate.

Second Trimester

The second trimester is usually considered to be from weeks 13 through 28. During my second trimester, I felt great! I had so much energy and I felt like I could conquer the world. My body was doing the most amazing thing (creating a life) and I was totally there for it! The best part was that there was no more nausea!

This is the time when you start to show that you’re pregnant and a few brave people start tentatively asking you about it. According to my pregnancy journal, I started showing around week 13 and started wearing maternity clothes at week 16. This varies, of course, woman to woman and pregnancy to pregnancy (many women find that they start showing earlier if they’ve been pregnant before).

You may start to feel some back pain and pain in your pelvis. The pain in your pelvis is called round ligament pain and, yes, it is quite a pain. Round ligament pain is a sharp pain on one or both sides that can be brought on my sudden movements, such as coughing or sneezing. It is very common in pregnancy and results from the stretching of the ligaments that support the uterus. Acetaminophen can help with the pain, but always be sure to check with your doctor before taking any medication during pregnancy.

By week 20, I began to feel a bit dizzy sometimes. From my pregnancy journal: “I’ve been trying to go about my life the same way I always have, but I’ve been getting dizzy and faint in the morning either walking up the stairs or walking to the building from the parking lot.” I almost fainted on more than one occasion walking from my car to a building. I asked my doctor about it and he suggested maybe that I was dehydrated, so I began making sure I was hydrated before going anywhere. That may have helped a bit, I’m not really sure. What I do know is that I should have pushed for a handicapped parking permit because a pregnant woman passing out on the cement is a situation that should be avoided.

The best part of the second trimester for me was feeling my babies (I had a twin pregnancy) start to move. It felt like a flutter, like little butterfly bubbles floating up through my belly. Sometimes I wish I was pregnant again just to feel that magical feeling.

Third Trimester

The third trimester is from about week 28 to the end of your pregnancy. This is the trimester in which every person who sees you feels compelled to reach out and touch your belly. I didn’t mind, but if you are not comfortable with that, you have every right to let people know your boundaries. Also, you are going to keep getting bigger and bigger (even though you think there is no way your body could possibly expand any more than it already has).

Some of the great (and not-so-great) things you will likely encounter during this trimester include back pain, round ligament pain, swelling, hemorrhoids, shortness of breath, heartburn, and frequent urination. Some pregnant women experience carpal tunnel syndrome or De Quervain’s Tenosynovitis as a result of swelling around the tendons in the wrist. Potential complications in the third trimester include gestational diabetes, iron-deficiency anemia, and pre-eclampsia. You will also begin to feel Braxton-Hicks contractions. These contractions don’t dilate your cervix. They are your body’s way of practicing for the real deal.

My twin pregnancy ended at week 32 with an emergent C-section due to the onset of early labor and my babies’ wildly fluctuating heart rates. After a few weeks in the NICU, they were able to come home. After 10 years, they’re doing great!

Janette DeFelice
Dr. Janette DeFelice is a writer currently focusing on how the changing environment affects our health. She holds a Doctor of Medicine degree from Chicago Medical School where she taught clinical and diagnostic skills to beginning medical students, and a Master’s degree in Humanities from the University of Chicago. She also has a Bachelor’s degree in Political Science. Her writing can be seen online at BeTheChangeMom, ChicagoNow, and Medium, and she’s very excited to have published her first novel, Delia Rising: A Ballet in Three Acts. She lives in Chicago’s west suburbs with her school-age twins, her husband, and a family cat named Clara Barton.

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