Week 4 of Your Pregnancy

Verywell / Bailey Mariner

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At 4 weeks pregnant, the tiny life inside you (which is technically an embryo) is implanting in your uterus, where it will grow and develop over the next 36 weeks. Along with implantation in the uterine lining, comes a rise in the pregnancy hormone hCG. At the end of this week, there may be enough hCG to detect with a sensitive early home pregnancy test. Learn more about pregnancy symptoms and your baby's development at 4 weeks gestation.

4 Weeks Pregnant Is How Many Months? 1 month

Which Trimester? First trimester

How Many Weeks to Go? 36 weeks

Your Baby's Development at 4 Weeks

Starting at week 4, your baby is called an embryo. At just 0.2 mm, your little embryo is about the size of a poppy seed.

At 4 weeks pregnant, your baby is about the size of the hole in a baby bottle nipple
Verywell / Bailey Mariner 


When the fertilized egg is in the uterus and attaches to the uterine wall it is called implantation. Implantation usually takes place six to ten days after ovulation. So, if it didn't happen at the end of week 3, your budding baby will burrow into your uterine lining this week.

Early Development

There inside your fertilized egg are all the cells that will develop into your baby and what your baby needs to survive for the next nine months. The inner cells begin to transform into your baby’s organs and body parts. The outer cells start to form the placenta.

Stay Calm Mom: Episode 2

Watch all episodes of our Stay Calm Mom video series and follow along as our host Tiffany Small talks to a diverse group of women and top doctors to get real answers to the biggest pregnancy questions.


A Positive Pregnancy Test: Now What?

Your Common Symptoms This Week

It’s tough to tell if you’re having early pregnancy symptoms during week 4. Many of the first signs of pregnancy are the same as the common premenstrual symptoms. However, you may notice a triphasic basal body temperature pattern or implantation spotting. Of course, some people do not have any signs this early.  

PMS-Like Symptoms

Changing hormones in your body can cause symptoms similar to those you get before your period. Bloating, fatigue, mood changes, tender breasts, and even mild cramps are common signs of early pregnancy. 

Triphasic Chart

If you track your basal body temperature (BBT) on a chart, you may know that a consistent rise in temperature indicates ovulation. A chart showing ovulation has two phases or levels of temperatures.

Sometimes, there is a second rise or third level of consistent temperatures that begins about seven to twelve days after ovulation. A chart with three distinct temperature levels is called triphasic (three phases), and it’s a possible sign of pregnancy. But, it isn’t a definite sign since not all pregnancy charts show a triphasic pattern, and not all triphasic charts end in a pregnancy.

Implantation Spotting

Around the time your baby is implanting or burrowing into your uterus, you may experience a small amount of vaginal spotting or light bleeding. While you may mistake it for a lighter-than-normal menstrual flow, it may be your first sign of pregnancy. But, don't worry if you don’t have implantation spotting because not everyone will have or notice this symptom. 

Self-Care Tips

The wait to test is almost over, but it can still be stressful. So, use this time to try to stay busy and care for yourself.

Take Care of Yourself

Eating well, getting in a little physical exercise, and taking some extra time to rest can go a long way to help you combat symptoms such as fatigue and mood changes.

Stay Busy

If you find yourself anxiously waiting to take a pregnancy test, the time could seem to slow down to a halt. Try to keep busy and find other things to focus on to make the time go faster and give your mind a break from the testing thoughts.

Your Week 4 Checklist

Advice for Partners

It’s hard for partners to wait for the pregnancy test result, too. It’s natural for you both to be on edge. Take this time to distract yourselves together with some fun just-the-two-of-you activities.

Recommended Products

It’s almost time to take a pregnancy test. You may want to purchase one this week or early next week.

Pregnancy Tests

Your baby begins to produce hCG before it attaches to the uterus, but once implantation takes place, hCG levels in your body rise quickly. Sensitive early pregnancy tests can detect small amounts of hCG in your urine as early as 10 days after conception.

Special Considerations

When you’re excited about that possible positive result, it can be hard to wait. If you do take an early test, it might turn out exactly as you hoped. However, testing too soon could also lead to a false-negative or a false-positive result. 

A Negative Pregnancy Test

By the end of week 4, the level of the pregnancy hormone human chorionic gonadotropin (hCG) is rising in your body. As the hCG levels go up, it can sometimes (but not always) lead to early pregnancy symptoms. The thing is, there’s still likely not enough of the hormone present in your body to be detected by a pregnancy test yet. 

What Experts Say

“Many patients test too early, get a negative result, and then get the false impression that they are not pregnant.”

Allison Hill, MD, OB/GYN

Chemical Pregnancy

On the flip side, an early positive pregnancy test may indicate a chemical pregnancy. A chemical pregnancy is one that ends shortly after implantation. 

What Experts Say

“While some women may want to know about this loss, many don’t. It’s hard to wait. Uncertainty can be very anxiety-provoking, but there’s something to be said for accepting your lack of control. It can actually be a great relief.”

Shara Marrero Brofman, PsyD

A Word From Verywell

While it's still a week of waiting, incredible events are happening during week 4. By the end of the week, implantation will be complete, and you will have a little embryo. You may even receive some early positive news. 

Next week, the wait is finally over. When taken correctly, home pregnancy tests are about 99% accurate on the first day of a missed period. So, get ready for the official big news!

9 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Holly Pevzner
Holly Pevzner is an award-winning writer who specializes in health, nutrition, parenting, and family travel.