4 Weeks Pregnant: Week-by-Week Guide
4 Weeks Pregnant

4 Weeks Pregnant: Week-by-Week Guide

Congrats You're 4 weeks pregnant. You probably have a million questions and we’re here to help. Explore this week-by-week guide to find out what’s in store for your baby and your body in week 4 of pregnancy.

At 4 weeks pregnant:

  • Your baby is the size of a poppy seed
  • You’re officially at the beginning of your 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 — from next week, all sorts of amazing things will begin to grow, so it’s time to ensure you know what you need to eat to ensure you and your little bean is getting all the vitamins and minerals 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 with blood and ready to nourish the embryo.

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 it’s not a period, it’s part of the effect of implanting into the uterine wall.
  • If you haven’t done a pregnancy test yet, it’s probably time. Assuming it’s positive, be sure to begin scheduling prenatal visits with your doctor.
  • You may feel puffy and bloated, and possibly even starting to get morning sickness.

4 Weeks Pregnant Facts

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

Baby Size at 4 Weeks
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 adjusting to the new life it’s supporting. As your baby changes, you will too, and there are certain pregnancy symptoms you may experience at this time. Keep these week 4 pregnancy symptoms on your radar:

  • 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 — don’t worry, you 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.
  • The nauseating symptoms of morning sickness are coming (they are probably not happening yet) but by week 9 they’ll be appearing, and not just in the morning.
  • Your breasts and nipples will start to feel tender. There’s going to be a few changes and they want to give you a little warning sign that they’ll be playing a major part.


Being 4 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’re new to all of this, so you’ll need to make some inquiries as to find a good OBGYN in your area.
  • It’s time to quit those vices. Say goodbye to smoking and drinking.
  • What you eat from here-on-in can impact your baby’s development and consuming the right nutrients is vital. Check out a clear guide to foods to avoid for moms-to-be.

Week 4 Checklist: Plan Your Pregnancy

Be prepared. Explore our pregnancy checklist below and add these items to your to-do list this week.

To-Do Complete
Find your OB
Share the news with your partner, but keep it private for now
Start taking prenatal vitamins

If you’re interested in learning more about your pregnancy, explore our resources on pregnancy planning and what to you need to know about prenatal care.