4 Weeks Pregnant: First Signs of New Life

Your Amazing Journey at 4 Weeks Pregnant

Can You Take a Pregnancy Test Yet?

By now, many women can get a positive pregnancy test result. Home pregnancy tests detect the hormone hCG (human chorionic gonadotropin) in your urine. While some tests claim to work up to five days before your missed period, it’s best to wait until the first day of your missed period for the most accurate results. Testing too early could give you a false negative or a faint, unclear result.

Your Due Date: A Rough Estimate

Wondering when your little one might arrive? Your due date is typically calculated based on the first day of your last period or the date of conception. But keep in mind—only about 5% of babies are actually born on their due date. Most arrive within two weeks before or after.

Your Baby’s Incredible Growth

Your baby is no longer just a tiny ball of cells—it's now an embryo about the size of a poppy seed! As soon as the amniotic sac forms (around 10−12 days after fertilization), your little one officially transitions from a blastocyst to an embryo. Over the next six weeks, their nervous system, connective tissue, and organs will begin to develop at an astonishing pace.

Baby Development at 4 Weeks

Rapid Growth and Development

Now that implantation has happened, your baby is growing fast. Their cells are multiplying and organizing into two distinct layers—the hypoblast and the epiblast—which will later develop into all of their organs.

This is also the most vulnerable stage of pregnancy. Exposure to harmful substances like alcohol, smoking, drugs, or toxic chemicals can affect development. Even overheating (from hot tubs, saunas, or fevers) can increase the risk of neural tube defects, so it’s best to stay cool.

The Placenta and Amniotic Sac Begin Their Work

Your embryo’s outer cells are busy burrowing into the uterine lining to form the placenta. Tiny spaces are opening up so your blood can start flowing into this area, supplying your baby with oxygen and nutrients.

At the same time, the amniotic sac is forming, creating a protective bubble filled with fluid that will cushion your baby as they grow. Another key structure, the yolk sac, is also at work—it temporarily nourishes the embryo and helps produce early cells for the digestive and reproductive systems.

Could You Be Expecting Twins?

It’s still too early to tell, but if you’re curious, fraternal twins develop when two separate eggs are fertilized, while identical twins come from a single fertilized egg splitting into two. The chances of having twins are higher if you’ve undergone fertility treatments, have a family history of twins, or are over 30 years old.

Pregnancy Symptoms at Week 4

Not Feeling Pregnant Yet?

That’s completely normal! Many women don’t experience symptoms this early. By next week, about half of pregnant women will start noticing changes, but for most, symptoms don’t kick in until around week 6.

Tender, Swollen Breasts

One of the earliest signs of pregnancy is breast tenderness. Rising hormone levels increase blood flow, making your breasts feel swollen, sore, or tingly. You may also notice darkening of the nipples or more visible veins on your breasts.

Fatigue

If you’re feeling completely drained, you’re not alone. The dramatic rise in progesterone can make you feel unusually tired. Rest whenever you can—your body is working hard!

Nausea and Morning Sickness

Although it’s called «morning sickness,» nausea can strike at any time of day. It typically begins around week 6 but can start as early as week 4. About 80% of pregnant women experience nausea, and about half also have vomiting.

Bloating and Gas

Even though your belly isn’t showing yet, you might already feel bloated. Increased progesterone slows down digestion, leading to gas, bloating, and more frequent burping.

Mild Cramping

Some women experience light cramping as the embryo implants into the uterus. This is usually normal, but if you have severe cramps or bleeding, check in with your doctor.

Mood Swings

Hormonal changes, fatigue, and stress can make your emotions feel like a rollercoaster. This is completely normal, but if you’re feeling persistently down or overwhelmed, don’t hesitate to talk to your provider.

Pregnancy To-Do List at Week 4

✅ Schedule Your First Prenatal Appointment
Once you get a positive test, call your doctor or midwife to set up your first visit. Many providers schedule the first prenatal checkup around week 8, but if you have a medical condition or concerning symptoms (such as bleeding or severe nausea), they may want to see you sooner.

✅ Check That Your Medications Are Pregnancy-Safe
Some over-the-counter and prescription medications aren’t safe during pregnancy. If you’re currently taking any medication, talk to your doctor about whether you should continue, adjust, or switch to something safer.

✅ Ease Digestive Discomfort
If you’re dealing with gas or bloating, try eating smaller meals throughout the day, chewing slowly, and avoiding carbonated drinks and artificial sweeteners. Gentle movement, like a short walk or prenatal yoga, can also help.

✅ Prepare for the Journey Ahead
Now that you know you’re expecting, you might be wondering what’s next. Take a sneak peek at the months ahead and start learning about what to expect throughout your pregnancy.