Quick answer: At week 5 your baby is about the size of a sesame seed, roughly 4mm long, and the heart is beginning to form and may already be starting to beat, though it is far too early to detect on a scan. Contact your GP to confirm your pregnancy, take 400mcg of folic acid daily until 12 weeks, and stop drinking alcohol.
What parents need to know
Welcome to week 5 of your pregnancy! If you've just confirmed the news with a positive test, you may be feeling a wonderful mix of excitement and nerves — and perhaps the first stirrings of nausea. This week is a pivotal one: tiny but extraordinary things are happening inside you.
| Baby's size | About a sesame seed, roughly 4mm long |
|---|---|
| Folic acid | 400mcg daily until 12 weeks pregnant |
| Vitamin D | 10mcg daily throughout pregnancy |
| Caffeine limit | No more than 200mg per day |
| Booking appointment | Usually between 8 and 10 weeks |
How big is your baby at 5 weeks?
Your baby is about the size of a sesame seed — roughly 4mm long. At this stage, your baby is called an embryo. Small as that sounds, this tiny cluster of cells is already hard at work laying the foundations for an entire human being.
What's happening with your baby?
Week 5 is one of the most significant weeks in early development. The three primary layers of the embryo are forming, and each will eventually become different parts of your baby's body. The outer layer (ectoderm) will become the skin, hair, brain, and nervous system. The middle layer (mesoderm) will form the heart, muscles, and skeleton. The inner layer (endoderm) will eventually develop into the digestive system and lungs.
Perhaps the most exciting development this week is that your baby's heart is beginning to form and may already be starting to beat — though it's far too early to detect on a scan. The neural tube, which will become your baby's brain and spinal cord, is also starting to close. This is precisely why folic acid is so important right now, as it helps prevent neural tube defects such as spina bifida.
What's happening in your body?
By week 5, your period is late, and a pregnancy test will show a clear positive result. The hormone human chorionic gonadotropin (hCG) is being produced in increasing quantities by the developing placenta — this is what causes the test line to appear and what drives many of your early pregnancy symptoms.
Common symptoms at week 5 include breast tenderness (your breasts may feel heavier or more sensitive than usual), unusual fatigue as your body works hard to nurture your growing baby, and the beginnings of nausea or morning sickness, which often peaks between weeks 8 and 10. Some women also notice they need to wee more frequently, and mood changes are common thanks to shifting hormone levels. Not everyone experiences noticeable symptoms this early, and that is perfectly normal too — every pregnancy is different.
Important steps to take this week
Contact your GP
In the UK, your first step is to contact your GP surgery to confirm your pregnancy. Your GP will then refer you to a midwife for your booking appointment, which usually takes place between 8 and 10 weeks. Don't delay getting in touch — antenatal appointment slots can fill up, and you'll want plenty of time to register.
Start or continue folic acid
The NHS recommends taking 400 micrograms (mcg) of folic acid every day until you are 12 weeks pregnant. Folic acid significantly reduces the risk of neural tube defects. If you have conditions such as diabetes or epilepsy, or if there's a family history of neural tube defects, your GP may recommend a higher dose of 5mg daily — so do check with them. Vitamin D (10mcg daily) is also recommended throughout pregnancy.
Stop drinking alcohol
The NHS advises that no amount of alcohol is considered safe during pregnancy. Now is the time to stop completely if you haven't already. You should also reduce your caffeine intake to no more than 200mg per day — roughly one to two mugs of coffee or two to three cups of tea.
Eat well and listen to your body
If nausea is starting, eating little and often can help enormously. Plain crackers, ginger biscuits, or bland foods are often easier to manage. Cold foods are sometimes better tolerated than hot ones. Staying hydrated is important — try sipping water steadily throughout the day rather than drinking large amounts at once. If you're struggling to keep anything down, speak to your midwife or GP.
When to seek help
Light spotting around this time can occasionally occur and often isn't a cause for concern, but always mention it to your GP or midwife. If you experience heavy bleeding or severe cramping, contact your GP, midwife, or call NHS 111 for advice. If you have sharp or persistent pain on one side of your abdomen, seek medical attention promptly as this can occasionally be a sign of an ectopic pregnancy (a pregnancy implanted outside the womb), which requires urgent treatment.
Your week 5 checklist
- This week, aim to: contact your GP surgery to confirm your pregnancy.
- Start or continue taking 400mcg of folic acid and 10mcg of vitamin D daily.
- Stop drinking alcohol and reduce caffeine to under 200mg per day.
- Eat small, regular meals and stay hydrated.
- Make a note of any symptoms to discuss at your booking appointment.
Sources & further reading
- NHS — You and Your Baby at 5 Weeks Pregnant
- NHS — Folic Acid in Pregnancy
- Tommy's — Week 5 of Pregnancy
- NCT — Week 5 of Pregnancy
General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.
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