3 Weeks Pregnant: Week-by-Week Guide
3 Weeks Pregnant

3 Weeks Pregnant: Week-by-Week Guide

Congratulations! You’re pregnant. Sperm meets egg between weeks 2 and 3 and 23 X chromosomes and 23 Y chromosomes come together to create a little magic – a tiny version of you! At this stage of your journey, it’s all systems go. Explore this week-by-week guide to find out what’s in store for your baby and your body in week 3 of pregnancy.

At 3 weeks pregnant:

  • Your fertilized egg is the size of a grain of salt
  • You’re officially pregnant life’s about to get a little exciting
  • The countdown begins: you’ve got 37 weeks to go!

What happens during the third week of pregnancy?

  • It’s business time. The sperm and egg meet. Usually, during week 2 or 3 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 egg is fertilized by the sperm, conception has occurred.
  • Starting single. Your baby is a single cell called a zygote once the egg is fertilized. And though it’s a single cell, it has all the DNA needed for life, a full 23 chromosomes from your egg and another 23 from the sperm. These will determine your baby’s gender, hair, 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 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 nonidentical twins, triplets, or more.

What should I be feeling at 3 weeks pregnant?

  • There’s every chance at 3 weeks that you won’t even know that you’re pregnant unless you’ve really been trying. You won’t start showing in the belly department until around 12 weeks, but you can start to feel bloated around now.
  • As the cells of that little zygote start splitting, you may feel fatigued. It’s a timely reminder to start taking care of yourself and your nutrition.
  • The healthful food and prenatal supplements you consume will be the building blocks of your baby’s development, so ensure you’re taking in the ingredients to grow your baby’s brain. These include iron, zinc, iodine, copper, omega-3 fatty acids (DHA and EPA), selenium, vitamin A, choline and folate with experts recommending you get at least 200 milligrams (mg) of DHA per day.

3 Weeks Pregnant Facts

How big is your baby? Check out the chart below to find out! 

Baby Size at 3 Weeks
Baby Weight Teeny tiny
Baby Length Teeny tiny
Baby Size Comparable to a grain of sand or salt

Week 3 Pregnancy Symptoms

As it’s only week 3, most symptoms will not have started to appear. Here are a few signs you may notice now or that are going to be visible in the next couple of weeks.

  • Missed period. this is a good sign that if you don’t already realize it, you may be pregnant. At this point, you might want to buy a home pregnancy test to check.
  • Spotting and implantation bleeding. Don't worry, this may not be your period. Implantation bleeding is light bleeding or spotting that occurs between 7 and 14 days after. There’s no definitive way to know what the bleeding is, but the best way to know is to wait a few more days and take a pregnancy test. 
  • Nausea. the dreaded morning sickness may begin to rear its head, except it doesn’t limit its presence just to mornings (unfortunately) and if you end up blessed with twins you may even experience double the trouble with this early part of pregnancy symptoms.
  • Changes to your breasts. your nipples may darken, and breasts may feel sore and tender as they change in preparation for eventual feeding.


Being 3 weeks pregnant is an important time for you and your baby. Get advice on how to adjust to this new stage from the experts at Enfamil.

  • You won’t balloon to pregnant size immediately. Most women only gain up to five pounds in the first-trimester.
  • It’s likely that you won’t know you’re even pregnant this early as you probably haven’t missed your period.
  • When choosing a prenatal supplement, you may want to consider one that has docosahexaenoic acid (DHA). DHA is good for you, but it's important for your baby's brain and visual development. It is found naturally in fatty fish like salmon, but due to mercury levels in some fish, you may want to get it in the prenatal vitamin you’re taking anyway.

Week 3 Checklist: Plan Your Pregnancy

Be prepared for what’s coming up. Explore our pregnancy checklist below and add these items to your to-do list this week.

To-Do Complete
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
Keep taking prenatal vitamins with folic acid

If you’re interested in learning more about your pregnancy, explore our resources on pregnancy planning and get some pointers on what’s ahead during the first-trimester.