In week 4 of pregnancy, your body is beginning to form the placenta and amniotic sac.

Symptoms like abdominal pressure and tender breasts may appear this week, and as the cluster of cells that will soon become your baby burrows into your uterine lining, you may also spot some implantation bleeding. (But if you don't notice any symptoms at all yet, that's completely normal too.)

Your Baby at Week 4

At a Glance

Two sets of cells
Two sets of cells
Your itty bitty embryo has two layers of cells called the epiblast and the hypoblast. Soon they’ll develop into all of your baby’s body parts and systems.
Seeing double
Seeing double
You normally don't have your first ultrasound until at least week 6, but you might be able to spot the gestational sac as early as halfway through week 4 — and if you're having twins, you'll likely see two of them!
Baby's yolk sac
Baby's yolk sac
Before the placenta forms, you develop a yolk sac, which can be visible next week. This sac produces blood and helps to nourish your young embryo.

4 weeks pregnant is how many months?

If you’re 4 weeks pregnant, you're in month 1 of your pregnancy. Only 8 months to go! Still have questions? Here's some more information on how weeks, months and trimesters are broken down in pregnancy.

How big is my baby at 4 weeks?

Despite its extremely tiny size — no longer than 1 millimeter and no bigger than a poppy seed (think about that as you eat your morning bagel) — your little embryo is busy setting up house. You can keep track of your baby's growth each week with the What to Expect app.

Placenta and embryo begin forming

While you may have just started to wonder whether you're pregnant, your soon-to-be baby has already found its home: The blastocyst has completed its journey from your fallopian tube to your uterus.

Once there, it burrows into your uterine lining and implants — making that unbreakable connection to you that'll last the next eight months (and a lifetime after that).

As soon as that little ball of cells is settled in your uterus, it will undergo the great divide, splitting into two groups. Half of what's now called the embryo will become your son or daughter, while the other half forms the placenta, your baby's lifeline — which channels nutrients and carries waste away until delivery.

Development of the embryo and amniotic sac

While the amniotic sac (also called the bag of waters) forms around it, so does the yolk sac, which will later be incorporated into your baby's developing digestive tract.

The embryo now has three distinct layers of cells that will grow into specialized parts of your baby's body. The inner layer, known as the endoderm, will develop into your baby's digestive system, liver and lungs. The middle layer, called the mesoderm, will soon be your baby's heart, sex organs, bones, kidneys and muscles. And the outer layer, or ectoderm, will eventually form your baby's nervous system, hair, eyes and outer layer of skin.

Your Body at Week 4

baby size at 4 weeks pregnant

No symptoms yet?

Just a week after fertilization, baby-making is still in its infancy, so to speak. At 4 weeks pregnant, your body is gearing up, big-time — transforming quickly into a baby-growing haven that will house your little miracle for the next nine months or so.

Chances are you're oblivious to all the hubbub. While some women experience those pesky, PMS-like early pregnancy symptoms, including mood swings, bloating and cramping, others don't feel a thing.

Whatever you're feeling or not feeling, it may be too early to see a reliable result on your pregnancy test.

The egg implants

Though you may not feel pregnant quite yet, here's what's going on behind the scenes.

The fertilized egg and your uterus are making contact this week in a process called implantation, as the blastocyst you'll one day call your baby begins to attach itself to the uterine lining.

Up to 25 percent of the time, implantation bleeding will occur as that bundle of cells burrows its way into the uterine wall. Implantation bleeding, which is usually very scant and either light pink, light red or light brown, occurs earlier than your expected period. 

Don't mistake it for your period and don't worry about the bleeding — it's not a sign that something is wrong. You might feel a little pressure in your abdomen (nothing to worry about!) and your breasts may feel a little tender and become even bigger (but get ready for more growth spurts!).

Pregnancy hormones will soon make an appearance

Within six to 12 days after fertilization, the egg starts to release hCG, or human chorionic gonadotropin — the pregnancy hormone that will very soon turn that line on your pregnancy test pink or blue and your world upside down.

HCG alerts the corpus luteum (the once-follicle this egg was released from) that it needs to stick around and produce progesterone and estrogen to nourish the pregnancy until the placenta takes over about eight weeks from now.

Pregnancy Symptoms Week 4

Implantation bleeding
Implantation bleeding
PMS-like symptoms
PMS-like symptoms

Tips for You This Week

Take a prenatal vitamin

If you haven’t started taking a prenatal vitamin yet, now’s the time. (And no, a standard multi won’t do.) Prenatals contain vitamins and minerals that are essential for your growing baby.

For example, folic acid (aka folate) — which is found naturally in whole grains, green leafy vegetables, beans, bananas, broccoli and milk, and added via fortification to breads and cereals — is not only critical for neural tube development early in pregnancy but also for the development of your baby's brain during all nine months.

The best prenatal for you is the one that you can actually tolerate — which, for some people, may be a chewable or liquid option, or a softgel coated in gelatin.

Whichever prenatal you choose, make sure it hits, or comes close to, the recommended intake of folic acid, iron (if you can tolerate it), calcium, vitamin D, choline, omega-3 fatty acids, B vitamins and vitamin C.

Find your due date

Think you need a Ph.D. in quantum physics to figure out your due date? Doing the math is actually a lot easier than you think — even if you slept through high school algebra. Your estimated due date is 40 weeks from the first day of your last period.

Here's the slightly confusing part: If you do give birth on that day, your baby will have clocked in only 38 weeks in utero, not 40. That's because the pregnancy countdown begins two weeks before your baby is even conceived — making you about four weeks pregnant before you see a positive pregnancy test.

Regardless, you shouldn't plan your schedule around your estimated due date. After all, it is just an estimate. Most babies are born between 38 and 42 weeks, and babies of first-time moms are more likely to arrive on the later side. Only a handful of babies actually make their debuts right on schedule.

Does a faint line mean you’re pregnant?

If your pregnant test is showing a barely visible, faint line — one that looks more like a smudge of chalk — it usually means that implantation has occurred.

Still, you’ll want to take the test again in a few days or so to make sure the line has become thicker and darker, which means your pregnancy is progressing.

If you see a faint line on your pregnancy test but get your period later on, that means you were only briefly pregnant. In this case, you may have experienced a very early (and common) pregnancy loss called a chemical pregnancy. As upsetting as this may be, it won’t impact your ability to get pregnant in the future.

Can you choose the sex of your baby?

Priority number one is having a healthy baby. But it’s not uncommon to have your heart set on having a boy or girl, especially if you’ve already had a baby of the opposite sex. 

Unless you’re getting an assist from science — in the form of preimplantation genetic diagnosis (which is used along with IVF) or sperm sorting — there’s no real way to choose the sex of your baby

That said, some couples swear by the Shettles Method, which theorizes that having sex as close to ovulation as possible can net you a baby boy (Y-sperm are supposedly speedier); having sex two to three days before ovulation can yield a baby girl (X-sperm are supposedly slower but more resilient).

Here’s how long it takes to get pregnant

In general, healthy couples have a 20 to 25 percent chance of getting pregnant during each month’s cycle. The catch: That assumes you’re having sex “regularly” — two to three times a week — and without contraception. About 85 percent of couples who are trying to conceive will get pregnant within a year.

Once sperm meets egg, you can expect the process to go fairly quickly — it’ll take about two to three weeks for the fertilized egg to travel to the uterus and implant on the uterine wall, resulting in a pregnancy.

Know the symptoms of implantation

Once the fertilized egg travels down the fallopian tubes, it will implant into the wall of the uterus — a process aptly known as implantation. Many women don’t experience any symptoms of implantation, but some will feel abdominal cramps and light bleeding.

Whether you feel anything or not, implantation marks the beginning of your pregnancy. It won’t be long now!

Skip the DIY pregnancy tests

Drugstore pregnancy tests aren’t always cheap, but they are up to 99 percent accurate. Homemade pregnancy tests, on the other hand — while popular with bloggers and on YouTube — aren’t reliable at all (though they can be entertaining to try!).

The thinking goes that by combining your urine with salt, sugar, toothpaste, or even bleach, you can detect the presence of the pregnancy hormone human chorionic gonadotropin (hCG).

But there’s no evidence that these tests can yield an accurate result, and no major medical organization recommends using them. Still, if you want to try one for fun, have at it (as long as you go in knowing they're just for laughs).

From the What to Expect editorial team and Heidi Murkoff, author of What to Expect When You're Expecting. What to Expect follows strict reporting guidelines and uses only credible sources, such as peer-reviewed studies, academic research institutions and highly respected health organizations. Learn how we keep our content accurate and up-to-date by reading our medical review and editorial policy.

  1. What to Expect When You’re Expecting, 5th edition, Heidi Murkoff.
  2. WhatToExpect.com, What to Do About Bloating During Pregnancy, February 2021.
  3. WhatToExpect.com, Pregnancy Nutrition Chart: 32 Essential Nutrients for Pregnant Women, June 2022.
  4. American College of Obstetricians and Gynecologists, How Your Fetus Grows During Pregnancy, December 2021.
  5. National Institutes of Health, National Library of Medicine, Fetal Development, July 2021.
  6. National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development, How Do I Know If I’m Pregnant?, January 2017.
  7. National Institutes of Health, National Library of Medicine, The Basics of Brain Development, November 2010.
  8. Society for Endocrinology, Hormones of Pregnancy and Labour, March 2021.
  9. American College of Obstetricians and Gynecologists, Early Pregnancy Loss, May 2023.
  10. National Institutes of Health, National Library of Medicine, Pickles and Ice Cream! Food Cravings in Pregnancy: Hypotheses, Preliminary Evidence, and Directions for Future Research, September 2023.
  11. University of Rochester Medical Center, First Trimester Fatigue.
  12. American College of Obstetricians and Gynecologists, Morning Sickness: Nausea and Vomiting of Pregnancy, December 2021.
  13. UpToDate, Nausea and vomiting of pregnancy: Treatment and outcome, July 2023.
  14. National Institutes of Health, National Library of Medicine, Ptyalism Gravidarum, November 2009.
  15. Centers for Disease Control and Prevention, Toxoplasmosis: Pregnancy FAQs, December 2022.
  16. American College of Obstetricians and Gynecologists, Oral Health Care During Pregnancy and Through the Lifespan, August 2013, reaffirmed 2022.
  17. American Dental Association, Pregnancy and your dental health.
  18. FoodSafety.gov, People at Risk: Pregnant Women, September 2020.
  19. WhatToExpect.com, What Is Implantation Bleeding and When Does It Occur?, May 2023.
  20. WhatToExpect.com, How Many Weeks, Months and Trimesters in a Pregnancy?, May 2022.
  21. WhatToExpect.com, Pregnancy Symptoms: 14 Early Signs of Pregnancy, May 2023.
  22. WhatToExpect.com, What Is the Placenta? What This Organ Does and How It Forms, July 2021.
  23. WhatToExpect.com, How Babies "Digest" in the Womb, May 2021.
  24. WhatToExpect.com, Cramping During Pregnancy: Normal or Something More?, October 2022.
  25. WhatToExpect.com, Pregnancy Tests, August 2022.
  26. WhatToExpect.com, When Does Implantation Occur? Symptoms, What to Expect, May 2023.
  27. WhatToExpect.com, HCG Levels During Pregnancy: What Is Normal?, May 2021.
  28. WhatToExpect.com, Your Guide to Pregnancy Hormones, November 2022.
  29. WhatToExpect.com, The Best Prenatal Vitamins, According to Doctors and Registered Dietitians, October 2023.
  30. WhatToExpect.com, Pregnancy Due Date Calculator and Conception Calculator, September 2023.
  31. WhatToExpect.com, Does a Faint Line on a Pregnancy Test Mean It's Positive or Negative?, November 2022.
  32. WhatToExpect.com, How to Have a Boy or a Girl, March 2021.
  33. WhatToExpect.com, How Long Does It Take to Get Pregnant?, September 2022.
  34. WhatToExpect.com, What Is Fertilization?, July 2023.
  35. WhatToExpect.com, Pregnancy Test With Salt, May 2022.
  36. WhatToExpect.com, What Is the Sugar Pregnancy Test?, March 2022.
  37. WhatToExpect.com, Homemade Bleach Pregnancy Tests: Do They Really Work?, February 2022.

Recommended Products

What to Expect selects products based on real-life testing conducted by staff, contributors and members our user community, as well as independent research and expert feedback; learn more about our review process. Prices and details are accurate as of the published date. We may earn commissions from shopping links.

The 8 Best Prenatal Vitamins of 2024, Approved by OB/GYNs and Moms
View All
Nature Made Prenatal Multivitamin Folic Acid + DHA
See Now Opens a new window
Best Prenatal Vitamins - Nature Made Prenatal
Theralogix TheraNatal Core Preconception Vitamins
See Now Opens a new window
Best Prenatal Vitamins - TheraNatal Core Preconception Vitamin Supplement
New Chapter Advanced Perfect Prenatal Multivitamins
See Now Opens a new window
Best Prenatal Vitamins: New Chapter Prenatal Vitamins
Nordic Naturals Prenatal DHA
See Now Opens a new window
Best Prenatal Vitamins: Nordic Naturals DHA

What Other June 2025 Moms Are Talking About

join
There are 1,263 active discussions happening now with other June 2025 parents-to-be.
Join in