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Highlights this week

Calculate your due date!

Our due date calculator can determine your due date based on the date of your last menstrual period or the date of conception. Keep in mind that a due date is just a guess – only 1 out of 20 women actually delivers on her due date. You're just as likely to go into labor any day during the two weeks before or after.

From blastocyst to embryo

Your baby-to-be will soon transform from a ball of cells called a blastocyst to  an embryo the size of a poppy seed. (Once your amniotic sac forms, 10 to 12 days after fertilization, your baby becomes an official embryo.) Over the next six weeks, your baby’s nervous system, connective tissue, and organs will start to develop.

Consider carrier screening

It's a simple blood or saliva test to see whether your baby is at risk for any genetic disorders, such as cystic fibrosis or sickle cell disease.

4 weeks is how many months?

You're reaching the end of your first month!

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Baby development at 4 weeks

Growing fast

Cells are multiplying rapidly and taking on different functions. Your little embryo consists of two layers called the hypoblast and the epiblast, from which all of the organs will begin to develop over the next six weeks. This is the time when your baby will be most vulnerable to anything that might interfere with development, so be sure to steer clear of alcohol, smoking, drugs, and unsafe chemicals.

Watch out for overheating: High temperatures, especially early in pregnancy, have been associated with increased risk of neural tube defects. That's why saunas, steam baths, and body immersion in hot tubs aren't recommended during pregnancy.

Primitive placenta

Your embryo's outer cells are tunneling into the lining of your uterus. Spaces form within this layer for your blood to flow into so that you'll be able to provide nutrients and oxygen to your growing baby.

Amniotic sac and yolk sac

The amniotic sac contains amniotic fluid and will enclose your baby and cushion them as they grow. The yolk sac will produce your baby's first red blood cells and blood vessels.

Having twins?

It's too soon to know. But it's still fun to see what fraternal twins look like in the womb this week. You can also learn about your likelihood of having twins or more.

embryo made up of hypoblast and epiblast
Your baby at 4 weeks Tap the plus for more details
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Your baby is about the size of a poppy seed

poppy seed

Pregnancy symptoms during week 4

No pregnancy symptoms?

Don't worry. Many women don't feel anything yet this week. By next week, about half of women will experience symptoms, but most early pregnancy symptoms don't start until about 6 weeks.

Tender, swollen breasts

Breast tenderness can be one of the earliest signs of pregnancy. It usually starts around 4 to 6 weeks and lasts through the first trimester. You may notice your breasts growing or your nipples darkening. Some women also see prominent blue or purple veins develop on their breasts in early pregnancy.


For many women, exhaustion is one of the first signs of pregnancy. Pregnancy fatigue affects almost all expecting moms in the first trimester, likely due to a dramatic rise in progesterone.

Nausea or vomiting

Despite the misleading name, morning sickness can strike at any time of day. It usually starts around 6 weeks of pregnancy but can begin as early as 4 weeks. Up to 80 percent of expecting moms experience nausea during pregnancy, and about half have both nausea and vomiting.

Gas and bloating

Increased progesterone levels may be slowing down your digestion and causing gas and bloating. Even weeks before you begin to show, you may belch or pass gas much more often, or have to unbutton your pants to relieve bloating.


Cramps during pregnancy are often nothing to worry about. In early pregnancy, some women feel implantation cramps (and can have some spotting) when the fertilized egg implants in the uterus. On the other hand, first trimester cramps along with other symptoms such as bleeding can be a sign of a problem such as an ectopic pregnancy or miscarriage. Find out when cramps warrant a call to your provider.

Mood swings

Hormones, stress, and exhaustion all contribute to mood swings during pregnancy, which can be strongest in the first trimester. Emotional upheaval is normal right now. But if your mood swings are becoming more frequent or more intense, or if they last longer than two weeks, talk to your healthcare provider. You may be among the 14 to 23 percent of women who battle mild to moderate depression during pregnancy.

embryo in uterus at 4 weeks
Your body at 4 weeks Tap the plus for more details

Pregnancy checklist at 4 weeks pregnant

Take a pregnancy test

If you haven't already, test now to confirm that you're pregnant. For the most accurate results, wait until a few days after you miss your period before you take a pregnancy test, use your first-morning pee so hCG levels are more concentrated, and follow the directions on your test carefully. If you get a negative result but your period hasn't come, wait a few days and test again.

Make a prenatal appointment

When you get a positive pregnancy test, call your doctor or midwife and schedule your first prenatal appointment. Many healthcare providers will schedule your first visit for when you're about 8 weeks pregnant. Some will see you sooner, particularly if you have a medical condition, have had problems with a pregnancy in the past, or are having symptoms such as vaginal bleeding, abdominal pain, or severe nausea and vomiting.

Make sure your medicine is pregnancy-safe

Always check with your healthcare provider before you take any kind of medicine during pregnancy – prescription medicine or even an over-the-counter (OTC) product. If you take medication currently, ask your provider if it's safe to use during pregnancy. Your doctor or midwife can help you find a good alternative if it isn't.

Soothe your digestive system

If you're plagued by gas, bloating, or an uncomfortable sensation in your gut, try eating smaller meals throughout the day. Eat slowly and chew your food well, don't drink too +much water during meals, and avoid carbonated beverages, gum, and the artificial sweetener sorbitol. Exercise, like walking or prenatal yoga, can also provide relief.

Find out what's in store throughout pregnancy.

You're pregnant! Now what? Get a sneak peek at the months ahead with our quick pregnancy overview.

4 weeks pregnant bellies

Although your belly is still weeks away from popping, if you're experiencing  bloating your normal jeans may feel uncomfortable now. Look for clothes that are loose-fitting at the waist, like leggings, joggers, sweats, and maxi dresses. You'll be glad you have them as your body starts to change. Your uterus will push up and out to accommodate your baby, which is why anything that buttons at the waist may soon feel intolerable.

This week's video


BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organizations, professional groups of doctors and other experts, and published studies in peer-reviewed journals. We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies.

ACOG. 2020. How your fetus grows during pregnancy. American College of Obstetricians and Gynecologists. https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy [Accessed June 2021]

FDA. 2019. Home use tests: Pregnancy. U.S. Food and Drug Administration. https://www.fda.gov/medical-devices/home-use-tests/pregnancy [Accessed June 2021]

March of Dimes. 2017. Prescription medicine during pregnancy. https://www.marchofdimes.org/pregnancy/prescription-medicine-during-pregnancy.aspx [Accessed June 2021]

Merck Manual. 2021. Stages of development of the fetus. https://www.merckmanuals.com/home/women-s-health-issues/normal-pregnancy/stages-of-development-of-the-fetus [Accessed June 2021]

MedlinePlus (ADAM). 2021. Fetal development. https://medlineplus.gov/ency/article/002398.htm [Accessed June 2021]

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Kate Marple is a writer and editor who specializes in health, pregnancy, and parenting content. She's passionate about translating complicated medical information into helpful pregnancy and parenting advice that's easy to understand. She lives in San Francisco with her family.
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