First trimester
5 weeks pregnant
Your baby is about the size of a sesame seed
By Clever Mum Parenting · Parenting guides
How big is the baby at 5 weeks pregnant?
At 5 weeks pregnant, your baby is about the size of a sesame seed. The neural tube — which becomes the brain and spinal cord — is forming, and a very early heart is beginning to beat. This is a critical developmental window, which is why folic acid matters most now. These are typical averages — your midwife's measurements are the ones that matter for your pregnancy.
What might you feel at 5 weeks?
Most people at 5 weeks notice some mix of the symptoms below — and plenty notice none of them. Pregnancy hormones (hCG) are rising fast, and this is when morning sickness, sore breasts and fatigue often begin. Some people feel completely normal, which is also fine. None of this is a diagnosis; contact your midwife if something worries you.
Common symptoms this week
- Nausea beginning (any time of day)
- Sore breasts
- Needing to wee more often
- Fatigue and mood swings
Symptom lists are typical, never exhaustive — and having none of them is normal too.
What should you do at 5 weeks pregnant?
The useful job this week is practical, not medical. Check any regular medicines with a pharmacist or GP, and avoid alcohol and smoking. There's no safe known level of alcohol in pregnancy. Pair it with the NHS week-by-week guide if you want a second description of the same stage.
Week 5 checklist
- Check any regular medicines with a pharmacist or GP
- Stop alcohol and smoking completely
- Note the first day of your last period — every appointment will ask for it
What else is useful at 5 weeks?
Use the week page for size and symptoms; use the guides below for the decisions that actually sit in this window — pay, packing, car seats, labour signs.
5 weeks pregnant: common questions
Is it normal to have no symptoms at 5 weeks pregnant?
Completely normal. Symptom timing and intensity vary enormously — some people feel very sick from week 5, others feel nothing until week 7 or 8, and a lucky few sail through with almost no sickness at all. Absence of symptoms says nothing about how the pregnancy is progressing.
How big is my baby at 5 weeks pregnant?
At 5 weeks, your baby is approximately the size of a sesame seed. These are approximate averages — every baby grows at its own pace.
What's happening at 5 weeks pregnant?
The neural tube — which becomes the brain and spinal cord — is forming, and a very early heart is beginning to beat. This is a critical developmental window, which is why folic acid matters most now. For you: pregnancy hormones (hcg) are rising fast, and this is when morning sickness, sore breasts and fatigue often begin. some people feel completely normal, which is also fine.
Which trimester is 5 weeks?
5 weeks pregnant is in the first trimester. The first trimester runs to the end of week 12, the second from weeks 13 to 26, and the third from week 27 to birth.
Sources & further reading
This is general information, not medical advice — every pregnancy is different. For anything that worries you, and for all your antenatal care, speak to your midwife or GP. If your baby's movements ever slow down or change, contact your maternity unit immediately, day or night. Reviewed August 2026.