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First trimester

5 weeks pregnant

At 5 weeks, the embryonic period is getting underway, when the baby's major organs and body systems begin to form. The brain, spinal cord and heart are starting to develop, and many people find out they're pregnant around now after a missed period.

This page covers 5 weeks 0 days to 5 weeks 6 days (5+0 to 5+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 5.

Botanical illustration of a sesame seed

About the size of a sesame seed

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

How your baby is developing

  • This is around the start of the embryonic period, when all the major systems and structures begin to develop. Cells multiply and start to take on specific jobs, becoming blood cells, kidney cells and nerve cells.1
  • The neural tube is forming. It will become the brain, spinal cord and the rest of the central nervous system.1,2,3
  • The heart is starting to form. The cells that will make up the heart begin to cluster and can start to pulse around weeks 5 to 6.2,3
  • The embryo already has some of its own blood vessels, and a string of them will become the umbilical cord. The placenta is also forming, and it will later supply nutrients and oxygen and remove waste. The digestive tract is starting to form too.1,3
  • The embryo grows rapidly, but it's still tiny: the NHS describes it as around 2 millimeters long.1,3

Changes you may notice

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

  • A late period is often the first sign. If your cycles aren't regular you may not notice it. Some people have light bleeding that could be implantation bleeding, but it's worth getting advice about any bleeding in pregnancy.3,4
  • Many people feel very tired in the first trimester. Other common early signs include sore breasts, nausea, needing to pee more often, a heightened sense of smell, and new food likes and dislikes. Not everyone has them.3,5
  • Nausea and vomiting, often called morning sickness, is very common in early pregnancy. It can happen at any time of day or night.6
  • Some people get food cravings and some don't. If you crave things that aren't food, such as dirt, talk to your midwife or doctor.3

Care around this week

  • The early weeks are when the developing baby is most at risk from things that can cause birth defects, such as certain medicines, illegal drug use, heavy alcohol use and infections like rubella. The NHS advises avoiding alcohol altogether. Review any medicines with your provider rather than stopping them on your own.1,3
  • In the US, a first prenatal visit is usually scheduled soon after a positive test. It often includes blood tests and questions about your health, medicines and family history. In the UK, the booking appointment usually takes place between 8 and 12 weeks.3,7,8
  • Ectopic pregnancy symptoms, if they happen, tend to develop between weeks 4 and 12. Get advice right away if you have a combination of symptoms such as pain low down on one side, vaginal bleeding or brown watery discharge, or pain in the tip of your shoulder.9

Questions to ask your provider

  • When will my first prenatal appointment be, and what will happen at it?
  • Are my current medicines and supplements OK to keep taking?
  • What can I do about nausea, and when should I call you about it?
  • Who should I contact if I have bleeding or pain before my first appointment?
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.11,12,13,14

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.4,13
  • 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.13,14,15,16
  • 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.13,17
  • 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.11,13,14
  • Sudden swelling of your face, hands or feet, or swelling, redness or pain in a leg.11,13,14
  • Belly pain that is severe or does not go away after resting, or pain just below the ribs.11,13,18
  • Regular tightenings or contractions, period-type pains, or backache that is unusual for you before 37 weeks, which can be signs of preterm labor.16,18
  • A fever of 100.4°F (38°C) or higher, or feeling hot, cold or shivery.13,14,16
  • Shortness of breath that comes on suddenly or happens when you lie flat, chest pain, a racing or pounding heart, or dizziness or fainting.13,14
  • Very itchy skin, especially on the palms of your hands or soles of your feet, or itching that is worse at night.19
  • 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.13,20
  • Thoughts of harming yourself or your baby. Get help right away, and call 911 or 999 if you think you might act on them.13,21

Questions about 5 weeks

Can you see a heartbeat on an ultrasound at 5 weeks?

Usually not yet. The heart is just starting to form, and a heartbeat most often can't be heard or seen on ultrasound until at least 6 to 7 weeks.3,7

Is it too early to take a pregnancy test at 5 weeks?

No. By now your period is usually late, and most home tests are reliable from the first day of a missed period.3,10

When should I call about morning sickness?

Contact your midwife, doctor or an urgent advice line if you can't keep food or fluids down for 24 hours, haven't peed in more than 8 hours or have very dark urine, feel very weak or faint, or vomit blood.6

Sources

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