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3 Weeks Pregnant: Week-by-Week Guide
5 mins read

IN THIS ARTICLE – At this stage of your journey, new developments are beginning to unfold. Check out this week-by-week guide to find out what’s in store for your baby and your body in week 3 of pregnancy.


Your baby at 3 weeks pregnant | Week 3 pregnancy symptoms | 3 expert tips for a healthy and safe pregnancy | Week 3 checklist: How to plan your pregnancy | Join Enfamil Family Beginnings



  • 3 weeks pregnant is which trimester? First trimester
  • How many weeks of pregnancy are left? 37 weeks
  • 3 weeks pregnant is how many months? You’re considered to be in the first month

With week 2 of your pregnancy complete, you’re on week 3. Enjoy it, as week 4 is on the horizon! 

One of the most exciting things about pregnancy is how many changes you’ll experience with your little one over the span of just 7 days! Here’s some tips and tricks to keep on top of all that’s happening.

Your baby at 3 weeks pregnant

What's happening in there

  • Your baby is the size of a grain of sand.
  • You’re officially pregnant. Life's about to get very exciting.
  • The countdown continues: you’ve got 37 weeks to go!

What happens during the 3rd week of pregnancy?

  • It's business time: The sperm and egg meet. Usually, during week two or three of pregnancy, the strongest sperm makes its way through the cervix (the opening of the uterus) and travels up the fallopian tubes to meet the egg. When the sperm fertilizes the egg, conception occurs.
  • Starting single: Once the egg is fertilized, your baby is known as a single cell called a zygote. Even though it’s a single cell, it has all the DNA needed for life, including 23 chromosomes from the egg and another 23 from the sperm. These 46 total chromosomes will determine your baby’s gender, hair color, eye color, physical features, and even a little of that personality you can’t wait to meet.
  • It's splitting time: As the zygote travels down the fallopian tube, it divides into many more cells, resulting in a big ball of cells called a blastocyst. The hard outside shell will become the placenta, nourishing and protecting what’s inside—the yet-to-be-formed embryo. Your baby is moving closer to a recognizable physical form and making a home in your uterus.
  • Twins?: If your ovaries release more than one egg, there’s a chance you’ll carry more than one baby. You could have non-identical twins, triplets, or more. 

What should I be feeling at 3 weeks pregnant?

  • There’s every chance that at three weeks, you won’t even know you’re pregnant unless you’ve been trying. You won’t start showing in the belly department until around 12 weeks, but you may begin to feel bloated.
  • The healthful food and prenatal supplements you consume will be building blocks of your baby’s development, so try your best to consume nutrients that will help your budding baby’s brain grow. These include iron, zinc, iodine, copper, omega-3 fatty acids (DHA and EPA), selenium, vitamin A, choline, and folate. The recommended amount of DHA is 200 mg per day.

Can you find out you're pregnant at 3 weeks pregnant?

  • You may test positive for pregnancy through an at-home test by the end of this week. If so, congratulations! You just finished your first three weeks of pregnancy.
  • Got a negative result? You may still be pregnant, but your body hasn’t produced enough of the human chorionic gonadotropin (hCG) hormone to be detected in your urine.
  • Whether you get a positive or negative test result, consider taking another test in a week to confirm.

How big is your baby at 3 weeks pregnant?

 3 Weeks Pregnant

Baby Weight

Teeny tiny

Baby Length

Teeny tiny

Baby Size

Comparable to a grain of sand or salt


Week 3 pregnancy symptoms

During week 3 of pregnancy, your body is changing quickly. As your baby grows, you will too, and there are certain pregnancy symptoms you may experience at this time.

  • Your missed period is a good sign that you may be pregnant. At this point, you might want to buy a home pregnancy test to check.
  • You may be experiencing spotting and implantation bleeding. Don't worry, this may not be your period. Implantation bleeding is light bleeding or spotting that occurs between seven and 14 days after conception. There’s no definitive way to know what the bleeding is, but the best way to find out is to wait a few more days and then take a pregnancy test.
  • Morning sickness may begin to rear its head, except it doesn’t limit its presence to just mornings (unfortunately). If you’re pregnant with twins, you may even experience double the trouble with this early pregnancy symptom.
  • Your nipples may darken, and your breasts may feel sore and tender as they change in preparation for eventual feeding.
  • You could be dreaming about ice cream … or maybe not. During the first three weeks of pregnancy, you may start to crave certain foods and develop strong aversions to others.
  • Bump? No. Bloated? Maybe. You probably won’t start showing until about 12 weeks, but bloating and gas can be common at three weeks.
  • Fatigue is natural. Your body is busy getting ready for your baby, which can take a toll on your energy.

3 expert tips for a healthy and safe pregnancy

Being 3 weeks pregnant is an important time for you and your baby. Here’s some more expert-recommended advice on how to adjust to this new stage and keep you and your baby safe.

  1. Weight gain: You won’t gain weight immediately. Most women only gain up to five pounds in the first trimester.
  2. Awaiting that missed period: You likely won’t even know you’re pregnant this early, since you probably haven’t missed your period.
  3. Choosing the right prenatal supplement: When choosing a prenatal supplement, consider one that has docosahexaenoic acid (DHA). DHA is good for you, and it's important for your baby's brain and visual development. DHA is found naturally in salmon, a fatty, low-mercury fish that’s safe to enjoy during pregnancy. Doctors encourage pregnant women to eat more low-mercury fish, including flounder and haddock. However, pregnant women should avoid high-mercury fish, such as marlin and swordfish. If you don’t like or can’t consume fish, prenatal supplements can complement your diet.

Week 3 checklist: How to plan your pregnancy

Knowing what to do week-by-week can help you feel prepared and alleviate stress. Add these new items to your to-do list this week. You’ve got this, mama!

To-Do Checklist
Take an early result test to see if you’re pregnant
Do your homework — Calculate your due date and read up on the first trimester


Learn more about your pregnancy, including pregnancy planning and pregnancy nutrition to feel prepared to continue this magical adventure. You’re armed with the facts, what to do, and now you can take time to connect with the little one growing inside you.

With week 2 in the rearview mirror and week 3 going strong, look to the future and what's coming up in week 4!

Join Enfamil Family Beginnings

You’re three weeks pregnant, and whether you are expecting or working on it, you can start preparing for all the excitement with Enfamil Family Beginnings. It’s the perfect resource for new and expecting moms. Save on Enfamil products, track your bump and baby’s growth, and get helpful articles each week relevant to your journey. Join now for up to $400 in free gifts.

All information on Enfamil, including but not limited to information about health, medical conditions, and nutrition, is intended for your general knowledge and is not a substitute for a healthcare professional's medical identification, advice, or management for specific medical conditions. You should seek medical care and consult your doctor or pediatrician for any specific health or nutrition issues. Never disregard professional medical advice or delay seeking medical treatment, care, or help because of information you have read on Enfamil.