Your pregnancy: 4 weeks

It’s official! About now, your pregnancy can be confirmed by a blood or urine test and you know for certain you have a baby on the way. Let us be among the first to say congratulations on getting pregnant!

By Today’s Parent

Updated Apr 03, 2025

Photo: Mandy Milks, Erik Putz, Anthony Swaneveld. Felt: thefeltstore.com

Congratulations, you’re pregnant! No really, you’re pregnant. At just four weeks pregnant, it may not feel “real” to you yet, but the chances that the plus sign or double lines on your home pregnancy test (or tests—we totally get the need to take a few!) were a false positive are slim to none. Your family doctor will order a blood test to confirm the pregnancy, but most women start with the pee-on-a-stick method at home. If you haven’t told your partner yet, now is the perfect time to get creative and have some fun when sharing the pregnancy news. 

And how is it that you’re already four weeks along? It can be confusing during the first month because pregnancy (which is an average of 40 weeks long) is actually measured from the first day of your last menstrual period. Even though you likely ovulated and conceived only two weeks ago, technically, you’re considered to be four weeks along. If you have an irregular cycle, your doctor can order a dating ultrasound to help calculate your due date more accurately (read more about what to expect at a dating ultrasound in week 6 of pregnancy). If you have a fairly predictable cycle, use our online due date calculator to tell you what date you’ll be counting down to.

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What’s going on in there: Fetal development at 4 weeks pregnant

At four weeks pregnant, your baby is still called an embryo, technically, and she is already growing and developing within the lining of your womb. She is the size of a poppy seed and made up of two layers of cells. There’s a gestational (or amniotic) sac, which keeps the embryo protected with fluid, and inside that, a yolk sac, which produces blood cells to nourish the baby until the placenta eventually takes over, usually when you’re around 12 weeks pregnant. As the umbilical cord starts to form, it transports nutrients and waste to and from your placenta to your baby. (Yup, it’s time to take a closer look at your diet, but we’ll talk about that more next week, in week 5 of pregnancy.) Your baby’s heart is already beating and her organs are developing—isn’t that amazing?

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Four weeks pregnant symptoms

Hello, hormones Maybe you took a test because your period was late (depending on the length of your cycle, most tests are effective four to five weeks from the first day of your last period) or because you were actively trying to get pregnant (in which case, yay!). But human chorionic gonadotropin (hCG), the pregnancy hormone that made the test turn positive, might already be causing a hodgepodge of symptoms that tipped you off, such as anxiety, nausea, vomiting, lightheadedness, dizziness, bloating, exhaustion and mood swings.

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The pregnancy hormone hCG also tells your ovaries to stop releasing eggs and increases the production of estrogen and progesterone, so you can blame your tender, sore and tingling breasts on it, too. You can read more about early pregnancy symptoms and signs here.

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Not everyone is the same

Some women are still symptom-free at this point in their pregnancies, but it’s nothing to be worried about. Every pregnancy is different, and symptoms can appear at any point in the early weeks—some lucky women experience very few symptoms at all.

Don’t be alarmed if you experience some mild cramping and an increase in vaginal discharge and/or spotting (also known as implantation bleeding), as the embryo is busy burrowing into the lining of your uterus. (A Costco-sized box of panty liners is a good idea to get you through your pregnancy because that increased pregnancy discharge is here to stay.)

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What’s on your mind this week

Life changing

A positive pregnancy test can deliver a big shock to you and your partner, even when it’s a planned pregnancy. Feeling overwhelmed (or, let’s be honest, panic-stricken) by the realization that you’re about to become parents is totally normal (Is your marriage ready for a baby?). Take time to talk to your partner (and to listen, too) about your fears and concerns. A lot of changes are headed your way, and speaking with trusted family and friends about their experiences (if you’re ready to share the news) can be helpful, too. Give yourself some time to let the news sink in and get used to the idea of becoming a mom.

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Early pregnancy loss

During the earliest weeks of pregnancy, concerns about miscarriage can dampen the excitement. Some women will get positive results on their pregnancy tests and then, a few days after their periods are due, experience really heavy periods. This is often an indication that a chemical pregnancy or early miscarriage has occurred. It’s estimated that 25 to 40 percent of pregnancies will end before they’ve been detected, especially if it’s very early on. We know that miscarriage isn’t caused by the mother and can’t be prevented. If you have any concerns about your symptoms, it’s best to seek the advice of your healthcare provider. We have links to miscarriage resources and support here. If you experience a loss, it’s important to know that you’re not alone: One in four pregnancies ends in miscarriage.

Just for kicks

In addition to these week-by-week articles about your pregnancy (make sure you sign up to get them emailed straight to your inbox!), you might want to check out one of these pregnancy-tracking apps.

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Pregnancy apps

CineMama

Have you seen those super-cool timelapse videos showing a pregnant belly growing bigger and bigger? With the right app, making one is much easier than you think. Use this one to take daily photos, add music and turn your months-in-the-making bun in the oven into a cute, shareable video showing the incredible transformation (plus the big reveal, of course). Apple, free.