Four Weeks Pregnant

You’re in week 4! Your body is beginning to form the placenta and amniotic sac, which both play significant roles in sustaining your growing fetus. You may also experience abdominal pressure and tender breasts, while implantation bleeding may accompany new pregnancy symptoms this week. Welcome to the world of pregnancy

Congratulations! Week 4 of pregnancy is a big milestone. You’re beginning to form the placenta and amniotic sac, which protect and support your little one as he or she develops. You may notice some of the most common early pregnancy signs, such as abdominal pressure and tender breasts. Or you may experience a light spotting of blood that you mistake for your period.

According to the American Pregnancy Association, in week 4 of pregnancy, your body is forming the fetus and placenta. For example, you may feel abdominal pressure or experience some tenderness on your breasts as fluid builds up to cushion your developing baby. Also, if you’ve been pregnant before and were aware of implantation bleeding, then you may notice it this week as well.

During week 4, the tiny life you and your partner created just a week ago is implanting and settling into its new home in your uterus, where it will grow and develop over the next 36 weeks. Along with implantation, 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.


Your Baby at Week 4

1:44Your Pregnancy Week 4Don’t have headphones?

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At a Glance

Two sets of cellsYour itty bitty embryo has two layers of cells called the epiblast and the hypoblast. Soon they’ll develop into all of your baby’s body parts and systems.

Seeing doubleYou normally don’t have your first ultrasound until at least week 6, but you might be able to spot the gestational sac as early as halfway through week 4 — and if you’re having twins, you’ll likely see two of them!

Baby’s yolk sacBefore the placenta forms, you develop a yolk sac, which can be visible next week. This sac produces blood and helps to nourish your young embryo.

4 weeks pregnant is how many months?

If you’re 4 weeks pregnant, you’re in month 1 of your pregnancy. Only 8 months to go! Still have questions? Here’s some more information on how weeks, months and trimesters are broken down in pregnancy.

How big is my baby at 4 weeks?

Despite its extremely tiny size — no longer than 1 millimeter and no bigger than a poppy seed (think about that as you eat your morning bagel) — your little embryo is busy setting up house.

Placenta and embryo begin forming

While you may have just started to wonder whether you’re pregnant, your soon-to-be baby has already found its home: The blastocyst has completed its journey from your fallopian tube to your uterus.

Once there, it burrows into your uterine lining and implants — making that unbreakable connection to you that’ll last the next eight months (and a lifetime after that).

As soon as that little ball of cells is settled in your uterus, it will undergo the great divide, splitting into two groups. Half of what’s now called the embryo will become your son or daughter, while the other half forms the placenta, your baby’s lifeline — which channels nutrients and carries waste away until delivery.

Development of the embryo and amniotic sac

While the amniotic sac (also called the bag of waters) forms around it, so does the yolk sac, which will later be incorporated into your baby’s developing digestive tract.

The embryo now has three distinct layers of cells that will grow into specialized parts of your baby’s body. The inner layer, known as the endoderm, will develop into your baby’s digestive system, liver and lungs. The middle layer, called the mesoderm, will soon be your baby’s heart, sex organs, bones, kidneys and muscles. And the outer layer, or ectoderm, will eventually form your baby’s nervous system, hair, eyes and outer layer of skin.

Your Body at Week 4

baby size at 4 weeks pregnant

No symptoms yet?

Just a week after fertilization, baby-making is still in its infancy, so to speak. At 4 weeks pregnant, your body is gearing up, big-time — transforming from a tried-and-true buddy to a weird and wacky science experiment.

Chances are you’re oblivious to all the hubbub. While some women experience those pesky, PMS-like early pregnancy symptoms, including mood swings, bloating and cramping, others don’t feel a thing.

Whatever you’re feeling or not feeling, it may be too early to see a reliable result on your pregnancy test.

The egg implants

Though you may not feel pregnant quite yet, here’s what’s going on behind the scenes.

The fertilized egg and your uterus are making contact this week in a process called implantation, as the blastocyst you’ll one day call your baby begins to attach itself to the uterine lining.

Up to 25 percent of the time, implantation bleeding will occur as that bundle of cells burrows its way into the uterine wall. Implantation bleeding, which is usually very scant and either light pink, light red or light brown, occurs earlier than your expected period. 

Don’t mistake it for your period and don’t worry about the bleeding — it’s not a sign that something is wrong. You might feel a little pressure in your abdomen (nothing to worry about!) and your breasts may feel a little tender and become even bigger (but get ready for more growth spurts!).

Pregnancy hormones will soon make an appearance

Within six to 12 days after fertilization, the egg starts to release hCG, or human chorionic gonadotropin — the pregnancy hormone that will very soon turn that line on your pregnancy test pink or blue and your world upside down.

HCG alerts the corpus luteum (the once-follicle this egg was released from) that it needs to stick around and produce progesterone and estrogen to nourish the pregnancy until the placenta takes over about eight weeks from now.

Pregnancy Symptoms Week 4

Implantation bleeding

PMS-like symptoms

Tips for You This Week

Don’t forget vitamin D

Most of your vitamin D supply comes from the sun or fortified milk. If you don’t drink the white stuff, you’ll need to find your D from other sources.

That’s because vitamin D is essential for maintaining healthy teeth and bones, and helps your body absorb calcium (and you already know why you need to absorb plenty of that).

You can find vitamin D in many prenatal vitamins as well as from fortified milk, fortified orange juice and egg yolks. Talk to your doctor about how much you need (600 IU is the standard recommendation among the expectant set, but some may need 1,000 IU or more).Find your due date

Think you need a Ph.D. in quantum physics to figure out your due date? Doing the math is actually a lot easier than you think — even if you slept through high school algebra. Your estimated due date is 40 weeks from the first day of your last period.

Here’s the slightly confusing part: If you do give birth on that day, your baby will have clocked in only 38 weeks in utero, not 40. That’s because the pregnancy countdown begins two weeks before your baby is even conceived — making you about four weeks pregnant before you see a positive pregnancy test.

Regardless, you shouldn’t plan your schedule around your estimated due date. After all, it is just an estimate. Most babies are born between 38 and 42 weeks, and babies of first-time moms are more likely to arrive on the later side. Only a handful of babies actually make their debuts right on schedule.

Learn more about how to calculate your due date.Healthy fats are good fats

Your baby needs some fat — especially essential fats like omega-3 fatty acids. DHA, one of those omega-3s, is a major component of the human brain and retina and it’s important for your baby’s developing brain and eyes.

You can get DHA from pregnancy-safe fish such as trout and wild salmon and from DHA-fortified eggs. If you can’t stomach fish, you can also find DHA in prenatal vitamins and supplements, including a vegetarian DHA made from flaxseed.Avoid secondhand smoke

You may not smoke, but if those around you do, there could still be risks to baby. Recent research has found that exposure to secondhand smoke may increase your risk of miscarriage, low birth weight, ectopic pregnancy and other complications. So try to steer clear as much as possible.Try a new comfort food

Often, what starts out as a comfort food (meaning one of the few things you can stomach) later becomes associated with nausea — and actually starts to trigger another round of the queasies because you’ve eaten so much of it.

If you’re so sick of saltine crackers that they’re actually beginning to make you sick, for example, switch to another comforting carb instead.Make a prenatal appointment

If you haven’t already, now’s the time to make your first doctor’s appointment! Some OB/GYNs ask that you wait until you’re at least 6 to 8 weeks pregnant before a visit, but since early prenatal care is so important, it’s best to get something on the calendar as soon as you have a positive pregnancy test.

Make sure to research the kind of doctor or midwife you really want first.Stave off food poisoning

You may be eating for two (or, more accurately, one and a fraction) these days, but your menu just got a whole lot smaller. The reason for cutting out sushi, runny eggs and raw cookie dough batter? To safeguard against foodborne illnesses like listeria and salmonella.

Some of the most common food poisoning culprits are undercooked proteins like poultry, eggs, meat or fish, and raw dairy or juices.

On the off chance that you are sickened by food poisoning from salmonella, the bug will likely have to run its (unpleasant) course. But don’t worry, because it’s unlikely that your baby will be in any danger.

Four Weeks Pregnant Symptoms

In week 4 of pregnancy, your body is beginning to form the placenta and amniotic sac.

Symptoms like abdominal pressure and tender breasts may appear this week, and as the cluster of cells that will soon become your baby burrows into your uterine lining, you may also spot some implantation bleeding. (But if you don’t notice any symptoms at all yet, that’s completely normal too.)

This week is full of important developments that ensure your future baby’s healthy growth. Your baby’s heart is beating steadily and you may be feeling abdominal pressure and tender breasts from this growing cluster of cells that will soon become your baby; some women may experience implantation bleeding this week.

You’ve entered the fourth week of your pregnancy, and with it a whole new set of symptoms and side effects. As the embryo burrows into your uterine lining, you may notice some slight spotting that looks like light menstrual flow. It’s often referred to as implantation bleeding. Today marks the last day you can have unprotected sex freely, as any further sexual activity could put you at risk. Luckily, you can still get tested for STIs without harming your baby during this time period.

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.1

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

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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.2

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.3

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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, fatiguemood changestender breasts, and even mild cramps are common signs of early pregnancy.4 

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.5

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.2 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.6

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.7The 6 Best Pregnancy Tests of 2022

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.8 

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.9 So, get ready for the official big news!

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