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4 Weeks Pregnant: Week-by-Week Guide
4 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 4 of pregnancy.


Your baby at 4 weeks pregnant | Week 4 pregnancy symptoms | 3 expert tips for a healthy and safe pregnancy | Week 4 checklist: How to plan your pregnancy | Join Enfamil Family Beginnings



  • 4 weeks pregnant is which trimester? First trimester
  • How many weeks of pregnancy are left? 36 weeks
  • 4 weeks pregnant is how many months? You’re considered to be in the first month

With week 3 of your pregnancy complete, you’re on week 4. Enjoy it, as week 5 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 4 weeks pregnant

What's happening in there

  • Your baby is the size of a poppy seed.
  • You’re officially at the beginning of the journey.
  • The countdown continues: you’ve got 36 weeks to go!

What happens during the 4th week of pregnancy?

  • It's all starting to happen: During the first four weeks of pregnancy, all sorts of amazing things begin to grow. It’s time to figure out what you need to eat so you and your little bean get all the vitamins and minerals required to fuel this wonderful process.
  • That's no embryo (yet): Right now, you’ve got a blastocyst growing (it sounds like a “Harry Potter” character). It’s a ball of cells with a hard outer shell and a soft inner shell. The outer shell implants in your uterus and will become the placenta, while the inner shell will be where the embryo—the future mini-you—will develop.
  • Planting the seed: This week, the blastocyst implants itself in your uterus. The lining is thick and ready to nourish the embryo.
Month 1 weeks 1-4: Over the next four weeks, your pregnancy journey officially begins.
Month 1 weeks 1-4: Over the next four weeks, your pregnancy journey officially begins.

What should I be feeling at 4 weeks pregnant?

  • This week is when the blastocyst finds a warm, nourishing place in the uterus to grow. It may lead to a little bleeding, but it’s not a period. It’s part of the effect of the blastocyst implanting into the uterine wall.
  • If you haven’t done a pregnancy test yet, it’s probably time. If it’s positive, be sure to begin scheduling prenatal visits with your doctor.
  • You may feel puffy and bloated, and possibly even start to get morning sickness.

How big is your baby at 4 weeks pregnant?

 4 Weeks Pregnant

Baby Weight

Too tiny to measure

Baby Length

Too tiny to measure

Baby Size

Comparable to a poppy seed


Week 4 pregnancy symptoms

During week 4 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.

8 common week 4 pregnancy symptoms

  • You’ll probably start feeling the symptoms that come with the production of progesterone, a pregnancy hormone that will take top billing in your life, dictating your moods and health.
  • You may feel a little puffy and bloated.
  • If you’re a first-time mom, your baby bump probably won’t be showing for a while yet.
  • There may be some spotting or light bleeding.
  • You will probably experience some epic mood swings as the hormones kick into gear.
  • Your breasts and nipples will start to feel tender. They’re giving you a little warning sign that they’ll be playing a major part.
  • Looking forward to that pregnancy glow? At four weeks, you may start to notice some skin changes, including a luminous glow and natural flush, but most women won’t experience them until the third trimester.
  • Hormones and your baby’s incredible changes and growing needs may drain your energy, causing fatigue.

You may also have no symptoms yet, and that’s OK. Many early pregnancy symptoms begin popping up around week six.

Can morning sickness start at 4 weeks pregnant?

You probably won’t experience morning sickness during your first four weeks of pregnancy, but it’s coming. Nausea usually kicks in between weeks six and nine, and not just in the morning.

3 expert tips for a healthy and safe pregnancy

Being 4 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. New territory: You’re new to all of this, so make some inquiries to find a good OB/GYN in your area.
  2. Quitting bad habits: It’s time to quit those vices. Say goodbye to smoking and drinking.
  3. Food for thought: What you eat can impact your baby’s development. A nutritious and balanced diet is important. Check out a clear guide to foods to avoid when pregnant.

Week 4 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
Find your OB
Share the news with your partner, but keep it private for now
Start taking prenatal vitamins


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 3 in the rearview mirror and week 4 going strong, look to the future and what's coming up in week 5!

Join Enfamil Family Beginnings

You’re four weeks pregnant and officially a “mom-to-be.” Start preparing for your new arrival 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.