What Week Starts The Third Trimester? Your Final Stretch Starts Now

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By the time you're getting ready to close down your second trimester, your body is already beginning to feel the weight and time of pregnancy. At first, it seemed to fly by, but as the days begin to feel longer and longer with the heavy fullness of your body pressing ever downward onto you, time begins to stretch interminably with no end on the horizon. At what point are you in the homestretch, ready to complete this journey? What week starts the third trimester, and thus signals your upcoming birth and entrance into an entirely new phase in life?

Pregnancy is divided into three trimesters each lasting around three months, according to Mayo Clinic. The first trimester is between week one and week 12, the second trimester is weeks 13 to 27, and the third trimester — the homestretch — begins at week 28. While the actual dates are fairly arbitrary when it comes to fetal development and growth, they are nevertheless important for setting a frame around a period of time when specific development is expected to occur.

To me, the third trimester felt like the longest trimester. I was swollen, achy, and my hyperemesis hadn't let up. On top of that, I was in hardcore nesting mode, painting everything, cleaning every speck of dust, and organizing everything in my house. Beyoncé in a gold crown on stage I was not.

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But there's also a lot happening with your little one in the third trimester. Your baby is packing on the weight, Mayo Clinic reported, their lungs are developing rapidly, and they're even learning to blink. This becomes a really important skill when they're 9 years old and learn the "blink slowly before rolling eyes" technique to tell you that you just don't understand Minecraft and probably never will.

According to PLOS One, your baby goes through the single biggest growth spurt in its life during the third trimester, streching themselves upwards of 10 inches in just three months. Thankfully, unlike that growth spurt you hit in the eighth grade, this one won't lead to stretch marks behind their knees or weird bathing suit wardrobe malfunctions where you accidentally expose your breasts to that one goth kid you have a huge crush on but who acts like you don't exist until he finds out that you know all the words to every Blink-182 song. It's nothing like that.

According to the same article, your weight gain or maintenance is also key during the third trimester, often predicting the weight of your child, and other concerns, like whether or not you'll need a C-section to deliver your baby. Conditions like gestational diabetes and hyperemesis gravidarum are comorbidities of pregnancy which often play a part in the size of the neonate and ease of delivery.

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With the lung development comes lung movement that mimics true breathing. According to the American Journal of Obstetrics and Gynecology, this in-utero breathing that begins in the third trimester is a way to move vital fluid into the baby's lungs that builds up over time and aids in their development. From the first cry after birth, it's completely apparent that all of that breathing was good practice to keep you up long nights in the fourth trimester and beyond.

While the third trimester might feel like a drudging slog only to be endured and not enjoyed, it is actually crucial and very interesting to note how fast things progress in those final three months. Just remember, for however long it feels, it's really just a blip in time in your years as a parent, and hopefully you'll soon remember those weeks fondly.

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