8 Surprising Ways Your Pregnant Body Changes During the First Trimester

Caroline Olney | Feb 11, 2015 Pregnancy
8 Surprising Ways Your Pregnant Body Changes During the First Trimester

You know your body is going to change during your first trimester of pregnancy ... pretty obvious, right? Sure, you're going to gain some weight and start glowing (hopefully ...?), but what about all the big changes you can't see? 

That little creature inside of you is demanding attention already, and your body listens, changing in ways you never would have imagined.

#4 explains so much! Did you feel the effects?


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  • Your heart beats 15 beats per minute faster


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    Before pregnancy, the average resting heart rate for women is about 70 beats per minute (bpm). By 12 weeks of gestation, your heart is beating closer to 80-90 bpm. Why? Your body is creating more and more blood to accommodate all the growth and changes inside you. 

  • You inhale more


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    The term minute ventilation refers to the volume of gas (or, basically, air) inhaled or exhaled by your lungs per minute. During your first trimester of pregnancy, your minute ventilation increases by 50 percent. That’s a lot more air! 

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  • You grow a whole new organ


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    Yes, you are starting to grow a baby (good job!), but you’re also growing a placenta, which is the only transient organ in the human body. Weighing in at about one pound, the placenta is an endocrine organ, meaning that it excretes hormones vital to your pregnancy. It starts to form about a week after conception and produces hCG, the hormone that pregnancy tests look for. Speaking of ...

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  • Your body creates a brand new hormone


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    That would be hCG, the one we mentioned before. This causes a lot of changes during pregnancy, but the most obvious during the first trimester (and the most unpleasant) is morning sickness. 

  • Your arteries dilate and your blood flows faster


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    You've probably noticed that you have to pee a lot these days, right? Though there are a couple of reason for this, the biggest is that your arteries dialate and your blood flows faster, meaning that more blood reaches your kidneys, which in turn work harder and send more urine to your bladder. Eventually, your blood will flow 3.5 percent faster than it did when you weren't pregnant, and your arteries will widen to twice their normal size.

  • Your gallbladder grows


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    Yep, it actually gets bigger because of the increased amount of hormones (namely progesterone) in your body. Because it gets bigger, the gallbladder also gets sluggish, and your chances of constipation increase, along with a higher risk of gallstones.

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  • You produce 16 times as much progesterone


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    Progesterone is one of the most important pregnancy hormones, and it accounts for many of the most well-known first trimester symptoms, such as extreme fatigue and your pregnancy “glow”. Progesterone levels will increase throughout your pregnancy, but the most dramatic peak is during the first trimester.

  • Your body temperature increases


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    On average, a pregnant woman’s basal body temperature (resting body temp) will increase 0.4 degrees in the first trimester because of the hormonal changes occurring.

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