3 Weeks Pregnant

At 3 weeks pregnant, you may not even know you’re expecting yet, but big changes are underway. This is the week when fertilization typically occurs, and a single-cell zygote begins dividing into a blastocyst, which will soon implant in your uterus. While it’s too early for a positive pregnancy test, some people may notice subtle signs like mild cramping, bloating, or a heightened sense of smell. Hormones like hCG and progesterone are starting to rise, setting the stage for early pregnancy symptoms and supporting embryo development.

Here’s a quick overview of what’s happening at 3 weeks pregnant:

• Baby size. A cluster of cells, smaller than a grain of sand

• Key event. Fertilization and early cell division

• Symptoms. Most experience no symptoms at this stage, but if you do, they may include mild cramping, sore breasts, bloating, or spotting

• Hormones. hCG and progesterone begin to increase

• Test timing. Most home pregnancy tests won’t detect pregnancy until next week.

As your body gets ready to support a growing baby, understanding these early developments can help you navigate the exciting weeks ahead. Let's explore more of what to expect during week 3 of pregnancy. 

Highlights at 3 Weeks Pregnant

Here are a few things to look forward to and expect when you’re 3 weeks pregnant:

What Happens at Three Weeks Pregnant?

During the 3rd week of pregnancy, you're likely in the early stages of fertilization and implantation. This is typically the week when sperm meets egg, setting off a series of rapid biological events that mark the very beginning of pregnancy.

When the sperm fertilizes the egg—usually in the fallopian tube—a single-cell zygote is formed. This zygote contains 46 chromosomes: 23 from each parent. These chromosomes determine everything from your baby’s eye color to gender and even hair texture.

Shortly after fertilization, the single-cell zygote begins dividing, forming a cluster of cells known as a blastocyst. This microscopic ball of cells continues its journey down the fallopian tube toward the uterus, where it will ideally implant into the uterine lining. Implantation typically occurs later this week or early next week.

As it develops, it begins producing the hormone hCG (human chorionic gonadotropin)—the hormone detected by pregnancy tests. However, levels are usually still too low to get a positive result until week 4 of pregnancy or later.

How to Calculate Your Due Date

To calculate your due date:

• Add 280 days (40 weeks) from the first day of your last menstrual period (LMP).

• Or add 266 days (38 weeks) from conception.

Enter your LMP or conception date into our handy Due Date Calculator:

At 3 weeks pregnant, you’re still in month one of pregnancy. Monthly references are approximate, as medical tracking is generally based on weeks. It gets a little tricky, given that nine months doesn't divide evenly into weeks, but the first month of pregnancy typically includes the first four weeks. 

Signs and Symptoms at 3 Weeks Pregnant

Many people won’t experience signs of pregnancy at 3 weeks. Most early pregnancy symptoms typically begin around weeks 4 to 6, but at week 3, you might experience:

• Implantation bleeding and spotting

• Mild cramping and bloating

• Breast tenderness

• Light breakthrough discharge

• Elevated basal body temperature

• Very early fatigue or nausea.

Implantation Bleeding

Wondering, “When does implantation bleeding occur?” or “How many days after conception is implantation?” Implantation usually occurs 10 to 14 days after conception, when the fertilized egg attaches to the uterine wall, around week 4. This may cause light spotting. This bleeding is often pink or brown and lasts just a few hours to a couple of days. If bleeding is heavy or accompanied by pain, contact your healthcare provider/

Early Pregnancy Discharge

An increase in leukorrhea, a thin, milky-white vaginal discharge, is common and normal during pregnancy, and may occur when you’re around 3 weeks pregnant. If discharge is itchy or foul-smelling, consult your provider.

Morning Sickness in Pregnancy

Although morning sickness at 3 weeks pregnant is uncommon, some people do feel early nausea. So, when does morning sickness start in pregnancy? According to the American Pregnancy Association, up to 70% experience nausea during pregnancy, and this symptom often begins in early pregnancy, commonly between 4 and 9 weeks. 

Morning sickness may signal a healthy pregnancy, thanks to rising hCG and estrogen. So, while being 3 weeks pregnant and experiencing nausea is less typical, it can happen.

Cramping in Early Pregnancy

It's common to experience cramping in week 3 of pregnancy. Mild cramping or pulling sensations often accompany implantation as the blastocyst embeds in the uterine lining. So, if you’re three weeks pregnant and experiencing cramping, this is generally normal—think gentle, period-like cramps—but heavy pain or bleeding should prompt a call to your provider .

Breast Changes During Pregnancy

Breast changes during pregnancy—including tenderness, swelling, and sensitivity—may begin as early as 3 weeks pregnant as your body adjusts to hormonal changes. If you’re wondering about breast tenderness before a period vs early pregnancy sign, the soreness may feel similar, but more intense during pregnancy.

Breast tenderness is one of the earliest signs of pregnancy and may show up alongside fatigue or nausea.

3 Weeks Pregnant Belly

It’s common to wonder, “What does 3 weeks pregnant look like?” At 3 weeks pregnant, there's no visible baby bump yet—remember, it’s still early days. You may feel mild bloating, but your stomach at 3 weeks likely looks like it usually does. Changes are all happening on the inside. 

Here’s a general idea of how a baby bump may look during this first month. Remember, everyone is different!

How Big Is a Baby at 3 Weeks?

At 3 weeks pregnant, your baby is still in the earliest stages of development and looks more like a tiny cluster of cells than a recognizable baby. In fact, your baby is about the size of the head of a pin at 3 weeks—approximately .0019 inches (0.048 mm) long. While it's technically visible to the naked eye, it’s so small and tucked deep within your body that it can’t be seen without medical imaging.

3 Weeks Pregnant Ultrasound

At 3 weeks, it’s generally too early to detect anything with an ultrasound, as the fertilized egg is likely still traveling towards the uterus. A transvaginal ultrasound may show a thickened uterine lining at about 4 weeks.,

Can You Get a Positive Pregnancy Test at 3 Weeks?

Most home pregnancy tests detect hCG after implantation, which means around week 4 or later. At 3 weeks, hormone levels are typically too low for reliable detection. Waiting until after your missed period yields more accurate results.

3 Weeks Pregnant: Things to Consider

Even though your pregnancy is still in its earliest stage, there are some smart steps you can take to support your health and your baby’s development. At 3 weeks pregnant, your little one is just beginning to grow, and your body is preparing for the months ahead.

Here are a few key things to keep in mind:

3 Weeks Pregnant: Your Checklist

It may be early, but it’s a great time to start preparing! As you anticipate your new pregnancy, consider the following to-dos:

• Begin prenatal vitamins with folic acid

• Use the due date calculator above

• Note any spotting, cramping, or twinges

• Get help quitting if you smoke, drink, or take drugs

• Take a home pregnancy test after your missed period for the best results 

• Plan your first prenatal appointment after a confirmed pregnancy test

• Maintain healthy habits: diet, exercise, and safe supplements

• Take a look at what’s to come next week in our 4-week pregnant guide.

_{How We Wrote This Article The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.}