Week 5


Your Baby at 4 Weeks Pregnant

Baby’s growth and size

At this point, your baby is teeny tiny, only 0.2 mm or 0.04 inches. Think about that little hole in the tip of a bottle nipple – that’s about how small the baby is right now – wild!

What’s new developmentally? 

Congratulations mama, your baby is officially considered an embryo now! Your embryo is securely implanted in the lining of your uterus and is developing a yolk sac

This yolk sac will keep your embryo nourished until your placenta is formed – pretty cool, huh? A normal yolk sac, along with a few other factors, can confirm a healthy early pregnancy. 

Even though your baby is tiny, there are still some pretty incredible things going on, developmentally, at this point. 

In week 4, your placenta begins forming. It attaches to your uterine wall on one end and the baby’s umbilical cord on the other end.

About your placenta

Your placenta is an amazing organ that provides oxygen and nutrients to your growing baby. It also removes waste products from baby’s blood – seriously, our bodies never cease to amaze! 

You can expect your placenta to take over between weeks 8-12. By week 12, your placenta should fully be responsible for hormone production and providing nutrients. 

This is normally when *most* women with morning sickness start to experience some relief. You might even notice a little burst of energy too. Learn more in this article!

Fun facts about your week 4 baby

  • Your baby’s neural tube is already formed. The neural tube is essentially the building block of your baby’s spine, brain, and backbone aka super duper important 
  • Baby doesn’t have a heartbeat just yet. The earliest cardiac activity can be detected between five and six weeks via transvaginal ultrasound – but most women won’t have one quite that early
  • Baby is smaller than a poppyseed – so wild! 


Week 4 of Pregnancy 

Week 4 pregnancy symptoms 

You may or may not feel some very early pregnancy symptoms prior to your missed period including:

How should I be feeling at 4 weeks pregnant?

A lot of women don’t even know they are pregnant yet at this point, so you may be feeling pretty normal still! Most mamas report sore and tender breasts and/or bloating as their first early pregnancy sign. This is often a hallmark sign of your period, so you can see why it can be tricky to know for sure which it is. 

Everyone’s body is different and unique prior to pregnancy – you can expect the same for a pregnant body.  At 4 weeks, you likely won’t see any difference in the size of your belly. 

Keep in mind, bloating is fairly common early in pregnancy, so you might notice a little poof because of that. But don’t expect a real bump to pop out until your uterus moves up and out of your pelvis around weeks 12-16. 


More Week 4 Info

When should I take a pregnancy test?

It’s best to take a pregnancy test on the first day of your missed period for the most reliable results! If you wait until then, pregnancy tests are over 99% accurate.

Read more about different types of pregnancy tests (pink dye vs. blue dye, anyone?) and how they work in this article.

4 weeks pregnant ultrasound

Most women do not have an ultrasound until week 7 or 8 so don’t expect one quite this early. If your provider is recommending an ultrasound, it’s likely to look at the location of your gestational sac and to confirm your pregnancy. 

If you do have an ultrasound this early, expect it to be a transvaginal one. This means that your provider will insert a lubricated wand into your vagina to visualize the inside of your uterus and yolk sac. 

If your provider is unable to visualize the yolk sac, rest assured that it’s likely because it’s too early to see. There are other reasons this might be the case, but most commonly, it’s just because it’s too early and everything is just so tiny! 

First Trimester Prep Pack
First Trimester Prep Pack


4 Weeks Pregnant Belly


Tips for 4 Weeks Pregnant

  • Choose a provider for your birth – a lot of people don’t realize midwives aren’t just a home birthing thing. Learn about midwives vs. OBGYNs here
  • Decide where you’re going to give birth (yes, really!). This post from Instagram can help you know what to look for
  • Schedule your first prenatal appointment
  • Start taking a prenatal vitamin if you haven’t done so already – this is the one I took!
  • Familiarize yourself with early pregnancy symptoms and remedies to help you cope
  • Download all the fun pregnancy apps! Here I cover alllll the best ones
  • Call your insurance company to learn about your prenatal coverage if you aren’t familiar with it
  • Learn more about the do’s and don’ts of pregnancy and other things to do after that positive pregnancy test in this article!
  • Last, but definitely not least, sign up for MLN Weekly Pregnancy Updates to get free customized tips and updates sent straight to your inbox each week!


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