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First trimester

4 weeks pregnant

At 4 weeks, the blastocyst is settling into the lining of your womb, and the structures that will become the placenta and amniotic sac are forming. Your period would usually be due around now, so this is often when a home pregnancy test first turns positive.

This page covers 4 weeks 0 days to 4 weeks 6 days (4+0 to 4+6), counted from the first day of the last period. Check how far along you are

Enter it to see the calendar dates of your week 4.

Botanical illustration of a poppy seed

About the size of a poppy seed

Early embryos are measured in millimetres; see below for what is forming now.

How your baby is developing

  • Implantation continues. The blastocyst buries itself in the thick, blood-rich lining of the womb, sticks tightly to it and starts to receive nourishment from your blood.1,2
  • The beginnings of the placenta form from the outer layer of cells. Later, the placenta will provide oxygen and nutrients.2,3
  • A fluid-filled amniotic sac forms to cushion and protect the developing embryo. A tiny yolk sac is attached to the embryo and provides its nourishment at this early stage.2,3
  • By the end of this week, the developing embryo is still tiny: about 2 millimeters long, according to the NHS and Cleveland Clinic.2,3

Changes you may notice

Everyone’s experience is different. You may notice some of these, or none.

  • A missed period is often one of the first signs of pregnancy. If your cycles are irregular, you may not notice that your period is late.3,4
  • You may not have any symptoms yet. Early symptoms usually start around 4 to 6 weeks and can include tiredness, sore breasts, nausea, needing to pee more often and a metallic taste. Not everyone has all of them.3,5
  • Some people have light spotting or a very light bleed around the time their period is due, known as implantation bleeding. Mild cramping a bit like period pain can also happen. Get advice from a healthcare professional if you have any bleeding.3,5,6
  • You probably don't look pregnant. In a first pregnancy, a bump usually doesn't show until at least week 12.3

Care around this week

  • Home pregnancy tests detect the hormone hCG. Most are reliable from the first day of a missed period, and a positive result is almost certainly correct. A negative result is less reliable. If you still think you're pregnant, test again in a few days.7,8
  • In the US, a first prenatal visit is usually scheduled soon after you learn you're pregnant. In the UK, you can contact a GP or refer yourself to a midwife, and the booking appointment usually takes place between 8 and 12 weeks.3,9,10
  • If you have a long-term health condition, tell your doctor or specialist that you're pregnant as soon as possible. Don't stop any regular medicine without discussing it first. If the pregnancy is unplanned or you're unsure, you can talk confidentially with a healthcare professional about your options.3,7

Questions to ask your provider

  • When should my first prenatal or booking appointment be?
  • Should I keep taking my current medicines now that I'm pregnant?
  • Is the folic acid dose I'm taking right for me?
  • What should I do if I have bleeding or cramping?
When to contact your provider straight away

Call 911 (US) or 999 (UK) in an emergency, such as heavy bleeding or bleeding with severe pain, a seizure, chest pain, or severe trouble breathing.12,13,14,15

These symptoms are not always serious, but each one needs prompt advice from your provider, midwife or maternity unit (or NHS 111 in the UK if you cannot reach them) rather than waiting for your next appointment, and it helps to tell them you are pregnant.

  • Vaginal bleeding or spotting at any stage of pregnancy. Call 911 or 999 if the bleeding is heavy or comes with severe belly pain, shoulder pain, or feeling faint or dizzy.6,14
  • Fluid leaking or gushing from your vagina, or discharge that is unusual for you. Get checked straight away if the fluid is greenish, colored or smells bad.14,15,16,17
  • Your baby moving less than usual, not moving, or a change in their usual pattern of movements. Call immediately, even in the middle of the night, and do not use a home Doppler to check yourself.14,18
  • A severe headache that does not go away with simple painkillers or gets worse, or sudden changes in your vision such as blurring or seeing flashing lights.12,14,15
  • Sudden swelling of your face, hands or feet, or swelling, redness or pain in a leg.12,14,15
  • Belly pain that is severe or does not go away after resting, or pain just below the ribs.12,14,19
  • Regular tightenings or contractions, period-type pains, or backache that is unusual for you before 37 weeks, which can be signs of preterm labor.17,19
  • A fever of 100.4°F (38°C) or higher, or feeling hot, cold or shivery.14,15,17
  • Shortness of breath that comes on suddenly or happens when you lie flat, chest pain, a racing or pounding heart, or dizziness or fainting.14,15
  • Very itchy skin, especially on the palms of your hands or soles of your feet, or itching that is worse at night.20
  • Being sick so often that you cannot keep food or drink down, or signs of dehydration such as dark urine, peeing very little, or feeling dizzy.14,21
  • Thoughts of harming yourself or your baby. Get help right away, and call 911 or 999 if you think you might act on them.14,22

Questions about 4 weeks

Will a pregnancy test be positive at 4 weeks?

Often, yes. Most home tests work from the first day of a missed period, which is around now for many people. If a test is negative and your period still doesn't come, wait a few days and test again.7,8

Is it normal to have no symptoms at 4 weeks?

Yes. Early symptoms usually start around 4 to 6 weeks, and not everyone has them. You can still be pregnant without noticing any changes.3,5

Is cramping normal at 4 weeks pregnant?

Mild cramping a bit like period pain is listed as a common early symptom. Get advice right away if you also have bleeding, pain low down on one side of your tummy, or pain in the tip of your shoulder.3,6,11

Sources

  1. Fetal developmentUS National Library of Medicine
  2. Fetal development: week-by-week stages of pregnancyCleveland Clinic
  3. 4 weeks pregnant guideNHS Best Start in Life
  4. 5 weeks pregnant guideNHS Best Start in Life
  5. Signs and symptoms that might mean you're pregnantNHS (England)
  6. Vaginal bleeding in pregnancyNHS (England)
  7. Doing a pregnancy testNHS (England)
  8. Pregnancy testUS National Library of Medicine
  9. Prenatal care in your first trimesterUS National Library of Medicine
  10. Your antenatal appointmentsNHS (England)
  11. Ectopic pregnancyNHS (England)
  12. Pre-eclampsiaNHS (England)
  13. Epilepsy and pregnancyNHS (England)
  14. Urgent Maternal Warning Signs and Symptoms (Hear Her campaign)US Centers for Disease Control and Prevention
  15. Pregnancy symptoms you need to get help forNHS (England)
  16. Signs of going into labourNHS Best Start in Life
  17. Premature labour and birthNHS (England)
  18. Your baby's movementsNHS (England)
  19. Stomach pain in pregnancyNHS (England)
  20. Itching in pregnancyNHS (England)
  21. Severe vomiting in pregnancyNHS (England)
  22. Depression in pregnancyNHS (England)

Links checked November 12, 2026. Citing a source does not mean it endorses this site.

Written from the sources above and checked against them on 2026-11-12. Not reviewed by a clinician. Our editorial policy