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4 Weeks Pregnant
Updated on
February 22, 2024

4 Weeks Pregnant

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4 Weeks Pregnant.
4 Weeks Pregnant

At 4 weeks pregnant, implantation symptoms may kick in, and baby is turning from a blastocyst into an embryo.

At 4 weeks pregnant, you most likely haven’t missed your period just yet and might not be experiencing any symptoms, but there’s still a lot happening behind the scenes. Here’s what else you can expect at week 4 of pregnancy.

What To Expect At 4 Weeks Pregnant

How Many Months Is 4 Weeks Pregnant?

4 weeks pregnant in months is 1 month pregnant, which is part of the first trimester of pregnancy.

Your Baby at 4 Weeks

If you were to look at baby on an ultrasound at 4 weeks, you wouldn’t see much, but there’s actually a lot going on at this very early stage of your baby’s development. The fertilized egg has implanted into your uterus, and it’s quickly beginning to grow. (You may begin to experience some implantation symptoms associated with this.)

  • Splitting in two: This week, the blastocyst (which is basically a collection of cells) is splitting, eventually turning into your placenta (a whole new organ) and an embryo (hi, baby!).
  • Prepping for development: Even though it’s a tiny dot of a thing that can barely be seen on an ultrasound, the gestational sac carries blueprints for your baby’s nose, toes and just about everything else hidden in their chromosomes.

How Big is a Baby at 4 Weeks?

A 4-week baby is the size of a poppy seed.

4 Weeks Pregnant Ultrasound


At 4 weeks pregnant, it’s a bit too early for an ultrasound (that’ll come in a few weeks) but if you were to look at baby, this is what you’d see.

Your Body at 4 Weeks of Pregnancy

Not feeling symptoms yet? You’re not alone. Most people don’t start feeling pregnancy symptoms until later in the first trimester. But changes are happening! During the first trimester, hormones surge as your body works hard to start making a baby. Here are some of the earliest signs you may experience at 4 weeks pregnant.

4 Weeks Pregnant Symptoms

Many of the earliest pregnancy symptoms can feel like typical menstrual cycle symptoms, so it can be hard to know if it’s your period or a baby. Here are some symptoms you may notice in week 4:

PMS symptoms

In those early days, many people find pregnancy symptoms tough to decipher from typical PMS symptoms. After all, moodiness, fatigue, sore breasts, bloating and constipation can all be signs of PMS, as well as signs of implantation. But PMS eventually leads to a period and then goes away. Pregnancy symptoms linger—usually for the first trimester.

Missed period

Missing your period may be the first telltale sign of pregnancy and your motivation to take a pregnancy test.

Positive pregnancy test

Some home pregnancy tests are accurate at this point, but it could take another few days or even a week before you have enough Human Chorionic Gonadotropin (hCG), a pregnancy hormone, in your urine for an at-home test to detect. If the at-home test was negative, you could schedule a blood test (which is super sensitive) at your doctor’s office or lab, or test again a few days later with another test. If the at-home test was positive, you can feel pretty confident you’re pregnant.

Sore breasts

Before nausea, vomiting and extreme fatigue, many people experience sore or swollen breasts. It’s hard to believe that your body is already prepping for feeding a baby as early as 4 weeks, but it is.


As pregnancy hormones surge and your body starts to produce more blood to nourish baby, you’re bound to feel more than a little tired if not downright exhausted.


About 30% of people experience implantation bleeding when the embryo attaches to the wall of the uterus, so don’t be surprised if you have some light spotting. The bleeding tends to be a different color from a period, like light pink or dark brown.

Light cramps

Light cramping early in pregnancy can be normal. “Internal changes are happening to prepare the body to grow a baby for approximately nine months,” antenatal and postpartum doula Ana Genoa-Taney tells Babylist. These mild aches should only stick around for a day or two.

Pregnancy Symptoms Coming Up In Week 5:

You may be experiencing mood swings, have sore boobs or no symptoms at all in week 5 of pregnancy.

Top Tip for 4 Weeks Pregnant

Add a prenatal vitamin with 600 mcg of folic acid to your daily routine (if you aren’t already taking one). Folic acid protects against birth defects and may even lower your child’s blood pressure when they grow up.

Real Baby Bumps at 4 Weeks Pregnant


4-weeks-pregnant-bump-@faith in the wait








Commonly Asked Questions About 4 Weeks Pregnant

At 4 weeks pregnant, things are just beginning to happen and you might not even know you’re pregnant just yet. Here are some commonly asked questions people who are 4 weeks pregnant ask.

How can I tell the difference between PMS and pregnancy symptoms?

Premenstrual symptoms are very similar to signs of implantation, so the best way to tell the difference is to take a pregnancy test.

How accurate is an early positive pregnancy test?

According to the Cleveland Clinic, “you might get a positive from an at-home test as early as 10 days after conception.” Pregnancy tests detect hCG which will only be present in your urine if you’re pregnant. Congratulations!

When will my first doctor’s appointment be?

Most doctors will want to see you for your first prenatal appointment around week 8 or week 9. After that, you’ll go in roughly every 4 weeks until the last couple of months of pregnancy when appointment frequency increases. At this initial appointment, your doctor or midwife will likely ask about your medical history, take a quick peek at your baby via ultrasound and calculate your due date.

Your Pregnancy, Week by Week

Want to know what’s going on with both your baby and your body every week? Start your Babylist registry today and get friendly tips and expert advice delivered right to your inbox for each week of your pregnancy (and beyond!).

Recommended Products for Week 4 of Pregnancy

While you may not experience any pregnancy symptoms for a few weeks, and won’t be showing just yet here are some products you might want to have on hand.

4 Weeks Pregnant Checklist

  • Call your OB/GYN and make an appointment for your first prenatal visit, which will probably take place around week 8.
  • Whether you’ve been trying for months or this is a surprise, remember to take a deep breath. This is going to change everything, but that’s the point.


Babylist Staff

Babylist editors and writers are parents themselves and have years of experience writing and researching, coming from media outlets like Motherly, the SF Chronicle, the New York Times and the Daily Beast, and the fields of early childhood education and publishing. We research and test hundreds of products, survey real Babylist parents and consult reviews in order to recommend the best products and gear for your growing family.

This information is provided for educational and entertainment purposes only. We do not accept any responsibility for any liability, loss or risk, personal or otherwise, incurred as a consequence, directly or indirectly, from any information or advice contained here. Babylist may earn compensation from affiliate links in this content. Learn more about how we write Babylist content and review products, as well as the Babylist Health Advisory Board.