How many months is 4 weeks pregnant?

4 weeks pregnant puts you in month 1 of pregnancy. Week 4 is the last week of that month, and month 2 starts at week 5. Providers count in weeks; months are approximate.

How big is the baby at 4 weeks?

At 4 weeks, the baby is about the size of a poppy seed, roughly 0.2 cm long. That is an average; healthy babies vary.

What are normal hCG levels at 4 weeks pregnant?

Cleveland Clinic lists a typical range of 5 to 426 mIU/mL at 4 weeks from your last period. The range is very wide, and the embryo attaches on different days in different pregnancies, so two healthy pregnancies of the same age can have very different numbers. One result says little on its own. Providers look at how the level changes over two or three days. A lower-than-average number can still be a healthy pregnancy, so ask your provider what your own results mean.

Are you officially pregnant at 4 weeks?

Yes, by the way pregnancy is counted. Providers date it from the first day of your last period, so at 4 weeks you conceived about 2 weeks ago, and the embryo has usually just attached to the womb. A positive home test is almost always right. A negative one is less reliable this early. According to a US study, about 1 in 10 pregnancies were still too early to detect on the day the period was due, because the embryo hadn't attached yet. If your period still hasn't come, test again in a few days.

Can you feel a baby bump at 4 weeks?

No. At 4 weeks the embryo is about 2 mm long, and your womb is still small and tucked inside your pelvis, so there is nothing to see or feel from the outside. The NHS says that in a first pregnancy you may not start to show until at least week 12. In a later pregnancy it can be sooner, because your muscles may have been stretched before. A puffy or tight belly now is usually bloating, which is a common early symptom.

Is it normal to have no symptoms at 4 weeks pregnant?

Yes. The NHS says you may not have any symptoms at first, and that early signs typically begin somewhere between 4 and 6 weeks. Nausea often comes a little later: in a UK diary study of 363 women, it started about 39 days after the last period, on average. Feeling nothing is not a sign that something is wrong. How a pregnancy is going can only be checked with scans or blood tests, not by how you feel.

What should I be careful of at 4 weeks pregnant?

Keep taking 400 micrograms of folic acid every day until at least week 12. Stop drinking alcohol and stop smoking. If you take medicine for a long-term health problem, tell your doctor you're pregnant soon, but don't stop it without their advice. The NHS also suggests an STI check if you or your partner could have one, and 10 micrograms of vitamin D a day from October to early March. Staying active is good too: about 150 minutes of exercise a week is recommended.

4 Weeks Pregnant

At 4 weeks pregnant, your period is due or just late, and a missed period is often the first clue. The embryo has usually attached to the lining of your womb and is about 2 mm long, around the size of a poppy seed. It sits in a fluid-filled sac with a tiny yolk sac that feeds it, and its outer layer will go on to form the placenta. You may have sore breasts, tiredness or mild cramps, or no symptoms at all. This page covers why a 4-week ultrasound usually shows nothing yet, what hCG levels to expect, what bleeding or cramping can mean now, and what to be careful about.

What trimester is 4 weeks?

Week 4 is in the first trimester, which runs from week 1 to week 12. The second trimester starts at week 13, 9 weeks from now.

Week 4 — first trimester, month 1; 36 weeks to go until your due date.
Baby's size — about a poppy seed, ~0.2 cm.

Not sure it's 4 weeks? Try our due date calculator.

★ Implantation completes — a positive test is now possible.

How big is your baby at 4 weeks?

Size of a

poppy seed

Length, head to bottom

~0.2 cm

Weight

—

Baby development at week 4

The blastocyst implants into the uterine lining and becomes an embryo, with the beginnings of the placenta and amniotic sac. The pregnancy hormone hCG rises quickly now — usually enough that a sensitive home test taken around your missed period can pick it up. The embryo is about the size of a poppy seed.

What an ultrasound shows at 4 weeks

A scan at 4 weeks usually shows no pregnancy yet, even when your test is positive. The embryo is only about 2 mm long. On a vaginal scan, the first thing that can be seen is the gestational sac, a small dark circle inside the womb, and it usually becomes visible at around 5 weeks.

hCG explains why. A vaginal scan usually starts to show a pregnancy when hCG gets to somewhere between 1,500 and 2,000 mIU/mL. At 4 weeks, typical levels are far lower, usually no more than a few hundred. So an empty scan this early is expected and is not, by itself, a sign that something is wrong.

Most people don't need a scan this early. If you have pain or bleeding, your provider may compare two hCG blood tests taken two or three days apart. If hCG is above the level where a pregnancy should be seen but nothing shows in the womb, they may follow up closely to rule out an ectopic pregnancy, which grows outside the womb.

Your body at 4 weeks

A missed period (often the first clue)
Light implantation spotting for some
Tender, swollen breasts
Mild cramping and fatigue

Bleeding and cramping at 4 weeks

Mild cramps, a bit like period pain, are common at 4 weeks, and so is light spotting as the embryo settles into the womb lining. Implantation spotting is usually pink or brown, light enough for a panty liner, and stops within about two days. Because it often comes when your period is expected, it is easy to mistake for a light period.

Bleeding that is more like a period can have other causes. One is a very early miscarriage, sometimes called a chemical pregnancy. These are more common than many people think: in a US study that tested urine every day in women trying to conceive, 22% of pregnancies ended before they would have been noticed. Bleeding can also come from an ectopic pregnancy, which can cause watery, dark brown bleeding and pain low down on one side. Let your provider know about any bleeding at all. Heavy bleeding, severe pain, pain in the tip of your shoulder, or feeling faint needs urgent care.

Tips for week 4

Take a home pregnancy test from the first day of your missed period
Book your first prenatal appointment once you get a positive
Keep up folic acid and avoid alcohol, smoking, and raw/unpasteurised foods

4 Weeks Pregnant: your questions

What trimester is 4 weeks?: Week 4 is in the first trimester, which runs from week 1 to week 12. The second trimester starts at week 13, 9 weeks from now.
How many months is 4 weeks pregnant?: 4 weeks pregnant puts you in month 1 of pregnancy. Week 4 is the last week of that month, and month 2 starts at week 5. Providers count in weeks; months are approximate.
How big is the baby at 4 weeks?: At 4 weeks, the baby is about the size of a poppy seed, roughly 0.2 cm long. That is an average; healthy babies vary.
What are normal hCG levels at 4 weeks pregnant?: Cleveland Clinic lists a typical range of 5 to 426 mIU/mL at 4 weeks from your last period. The range is very wide, and the embryo attaches on different days in different pregnancies, so two healthy pregnancies of the same age can have very different numbers. One result says little on its own. Providers look at how the level changes over two or three days. A lower-than-average number can still be a healthy pregnancy, so ask your provider what your own results mean.
Are you officially pregnant at 4 weeks?: Yes, by the way pregnancy is counted. Providers date it from the first day of your last period, so at 4 weeks you conceived about 2 weeks ago, and the embryo has usually just attached to the womb. A positive home test is almost always right. A negative one is less reliable this early. According to a US study, about 1 in 10 pregnancies were still too early to detect on the day the period was due, because the embryo hadn't attached yet. If your period still hasn't come, test again in a few days.
Can you feel a baby bump at 4 weeks?: No. At 4 weeks the embryo is about 2 mm long, and your womb is still small and tucked inside your pelvis, so there is nothing to see or feel from the outside. The NHS says that in a first pregnancy you may not start to show until at least week 12. In a later pregnancy it can be sooner, because your muscles may have been stretched before. A puffy or tight belly now is usually bloating, which is a common early symptom.
Is it normal to have no symptoms at 4 weeks pregnant?: Yes. The NHS says you may not have any symptoms at first, and that early signs typically begin somewhere between 4 and 6 weeks. Nausea often comes a little later: in a UK diary study of 363 women, it started about 39 days after the last period, on average. Feeling nothing is not a sign that something is wrong. How a pregnancy is going can only be checked with scans or blood tests, not by how you feel.
What should I be careful of at 4 weeks pregnant?: Keep taking 400 micrograms of folic acid every day until at least week 12. Stop drinking alcohol and stop smoking. If you take medicine for a long-term health problem, tell your doctor you're pregnant soon, but don't stop it without their advice. The NHS also suggests an STI check if you or your partner could have one, and 10 micrograms of vitamin D a day from October to early March. Staying active is good too: about 150 minutes of exercise a week is recommended.

Useful at week 4

hCG levels by week — the full chart, from 3 weeks to birth
Pregnancy due date calculator — your due date from the first day of your last period
Chemical pregnancy — what a very early loss looks like and what comes next
Implantation bleeding — spotting versus a period at 4 weeks
Foods and activities to avoid — what to cut out now that your test is positive

← All weeks: the full pregnancy week-by-week guide

Sources

Checked against the following public guidance on October 2, 2026. Advice can differ between countries; your doctor, nurse or midwife can apply it to you.