Your First Trimester of Pregnancy
First Trimester of Pregnancy
September 2, 2020

First Trimester of Pregnancy

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First Trimester of Pregnancy

Congratulations, you’re pregnant! Now what? A lot happens during the first trimester of your pregnancy.

You’ll probably be on a rollercoaster of emotions—all those pregnancy hormones hard at work making your baby can take you on a wild emotional ride. You also might be feeling some morning sickness (which really can last all day), and feeling really, really, really tired. That’s all part of the first trimester journey. Here’s what you can expect during those first weeks.

First Trimester Weeks

4-12 (In case you’re wondering, here’s how to count your pregnancy weeks.)

Baby’s development in the first trimester

During the first trimester, your baby grows from the size of a poppy seed (.05”) to as big as a roll of film (2.1”) by week 12.

By 8 weeks, you should be able to hear their heartbeat at your prenatal appointment.

While your body is busy making a home for baby (the amniotic sac, placenta and the umbilical cord), your baby is hard at work growing. At 5 weeks, their major organs start developing. “Three types of tissue layers are being separated and will determine specific types or organs and tissues usually based on location in the body and function,” explains Dr. Kim Langdon, MD, OBGYN. “The early spinal cord, spinal bones and nerves start out as a neural tube that start to develop in the superficial layer, called the ectoderm. The middle layer (mesoderm) forms the heart that divided into four chambers to pump blood. The endoderm forms the lungs, intestines, urinary, genitals, liver, thyroid, and pancreas.”

“Within the first 8 weeks, the embryo develops rudimentary structures for all body systems—it’s at this point in gestation that one can observe a heartbeat,” says Dr. Kecia Gaither, MD, MPH, FACOG. If you see your healthcare provider around that time, you should be able to hear the heartbeat at your appointment.

At 10 weeks, your baby is now a fetus and no longer an embryo. “The first trimester is when all the organs are formed. Then once everything is formed, the rest of the pregnancy is how the fetus fully develops,” says Dr. Sarah Yamaguchi, MD, FACOG. This means all the building blocks are in place, and your baby will keep getting bigger and bigger. By now, their eyes are fully formed, though they won’t open them for awhile. And their teeth are in place, but you won’t see these little chompers until they’re about six months old.

By the end of your first trimester of pregnancy, baby might start sucking their thumb as they develop reflexes, their intestines are fully developed and their face is more babylike—just in time for your first ultrasound photos.

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First trimester pregnancy symptoms

“The most common early pregnancy symptoms are fatigue, breast tenderness, moodiness, constipation and nausea,” says Dr. Yamaguchi. Of course, pregnancy affects every body differently and what you experience might be different than someone else you know.

Morning Sickness

Morning sickness is a sign that you’re really, truly pregnant—but unfortunately, it feels like a hangover without any of the fun.

Thanks to rising levels of pregnancy hormones, including progesterone, human chorionic gonadotropin (HCG—the one that triggers the “plus” sign on your pregnancy test) and estrogen, you may find yourself dealing with serious nausea and vomiting morning, noon and night.

For most people, morning sickness begins around the fifth or sixth week of pregnancy, and peaks around week nine. It’s typically gone by your second trimester—though some are still feeling ill in their third trimester.

Most of the time, morning sickness is no cause for alarm. But if your symptoms are severe, dehydration can be a concern, so be sure to talk with your healthcare provider if you’re throwing up multiple times a day, for several days in a row, for example.

In addition to feeling queasy, many pregnant people also find themselves with strong aversions to certain food or smells. “Eating small, frequent meals can help,” notes Dr. Yamaguchi. On the flip side, it’s a cliche, but pregnancy cravings are real.

Here are some tips on how to survive morning sickness.


During the first trimester, you’re pumping out more progesterone to build up the uterine lining and prevent miscarriage, and these higher levels can also can lower your blood pressure and blood sugar, making you feel lethargic. There’s a good chance you’ve never been so tired! “There is not a lot you can do about fatigue, other than rest,” says Dr. Yamaguchi. “Even then, I find most patients are still tired,” she adds.

This fatigue can make it hard to function, so try to make sleep a priority. Here are a few tips:

  • Take naps whenever possible
  • Make your bedtime an early one
  • Keep your bedroom dark and cool
  • Steer clear of TV or phone screens while in bed in order to make the sleep you do get more restful.

The good news is that this exhaustion, like morning sickness, should pass after the first trimester. In fact, many women get a burst of energy during the second trimester (though fatigue does return during the third trimester as your baby gets bigger and your body gets ready for labor).

Tender breasts

Notice anything different about your breasts lately? They may be getting a lot bigger, as well as super sore and sensitive to the touch. That’s those pregnancy hormones at work again.

While the tenderness will subside after your first trimester, they’ll continue to grow and change throughout your pregnancy in preparation for breastfeeding.

“For breast tenderness, I recommend making sure your bra is fitting you well and is supportive,” Dr. Yamaguchi tells us.

Now’s a good time to invest in a comfortable, supportive bra (or three). You may find non-underwire bras feel better on sore breasts. A nursing bra or sleep bra can be good bets—buy ones that are bigger or have extra hook-and-eye closures so you can continue wearing them throughout your pregnancy and postpartum.

Your emotions

Your emotions likely are all over the place during your first trimester. Once you find out you’re pregnant, you may experience excitement and joy, fear and nervousness. Add to the mix all those hormones, extreme fatigue and nausea from morning sickness, and you have the perfect recipe for crazy mood swings.

Even if you’re really excited about being pregnant, it’s natural to be worried about all the other things that come along with having a baby.

You may feel overwhelmed at times, and that is perfectly normal. Even if you’re really excited about being pregnant and welcoming a new baby, it’s natural to be worried about your baby’s development, how your life is going to change and all the other things that come along with having a baby.

Now’s the time to be good to you. Self care—naps, face masks, taking walks or whatever makes you happy—can help you feel like yourself, even if you’re bursting into tears at the slightest thing. Talk with other parents, your friends or your partner about how you’re feeling.

If you’re unable to feel any joy or are feeling hopeless, be sure to talk to your healthcare provider. They can help you find the support you need.


If you’re feeling blocked up, know you’re not alone. Constipation is very common during the first trimester. Up your fiber intake—snack on foods like dried fruit, raspberries and blackberries or oatmeal. And don’t forget to drink plenty of water.

The need to pee

You may find yourself running to the bathroom way more often than you used to once you’re pregnant. As your hormones fluctuate (notice a theme here?), you’ll have to go—a lot. Despite the frequent need to pee, it’s important to stay hydrated, though you might want to limit how much you drink before bed to avoid getting up all night long.

Weight gain in the first trimester

You’ll probably gain between 3-4 lbs during the first trimester. Your baby is still small, and, if you’ve been experiencing morning sickness and have trouble keeping food down, you may not gain that much. You may even lose a few pounds. As long as you’re seeing your healthcare provider, it shouldn’t be cause for worry. You’ll make it up in the second trimester.

First Trimester Pregnancy Checklist

  • Take a pregnancy test (and another one!) to make sure you’re really pregnant.
  • Choose a healthcare provider.
  • Make your first prenatal appointment.
  • Check your health insurance to see what prenatal care and birth costs are covered.
  • Buy prenatal vitamins. While these don’t replace a balanced diet, prenatal vitamins are packed with the extra nutrients, like folic acid, iron and calcium, needed for pregnancy.
  • Research which, if any, prenatal tests you might opt for during your pregnancy.
  • Get rest. Take naps, go to bed early, sleep in on the weekends. Do what you need to do to make it through.
  • Start creating your budget and savings plan for pregnancy and the first year of baby’s life.
  • Schedule your appointment for your 12-week ultrasound/nuchal screening test.
  • Research your work’s maternity leave policy and plan how to tell them you’re pregnant.
  • Your pants may be feeling tight toward the end of your first trimester. Start shopping for some maternity clothes. (Hint: leggings are a lifesaver.)
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