5 Weeks Pregnant: Baby Development
Five weeks is often when pregnancy starts to feel real — you've likely just had a positive test, and although there's nothing to see on the outside yet, a huge amount of early development is already underway. Here's what's happening with your baby and your body this week, and what to do next.
Baby's Development at 5 Weeks
At 5 weeks, your baby (still officially called an embryo at this stage) is roughly the size of a sesame seed. Despite the tiny size, this is one of the busiest weeks of development in the entire pregnancy:
- The neural tube is forming and starting to close — this will become the brain and spinal cord, which is exactly why folic acid is so important in these early weeks.
- The heart is beginning to take shape and will start its first faint beats very soon, often detectable on a scan from around 6 weeks.
- The placenta and umbilical cord are developing, building the connection that will nourish your baby for the rest of the pregnancy.
- Three distinct layers of cells are forming, which will eventually give rise to every organ and tissue in your baby's body.
Your Body at 5 Weeks
Even though you won't be showing yet, your body is working hard behind the scenes as hormone levels rise quickly. Common experiences at this stage include:
- Fatigue that can feel sudden and overwhelming, even if you were sleeping well before
- Breast tenderness or sensitivity, similar to premenstrual symptoms but often more pronounced
- Early nausea or "morning sickness," which can start any time from around now and, despite the name, can strike at any point in the day
- Needing the toilet more often, as hormone changes affect your bladder
- A heightened sense of smell, which can make certain foods or scents suddenly unbearable
Everyone's experience is different — some people notice several of these symptoms strongly, while others have very few at 5 weeks, and that's entirely normal too.
What to Do This Week
- Book your booking appointment with your GP or local midwifery service — you don't need to wait for a scan to do this.
- Keep taking a 400 microgram folic acid supplement every day until at least week 12.
- Take a 10 microgram vitamin D supplement daily, as recommended for all pregnant women in the UK.
- Avoid alcohol and smoking, and limit caffeine to around 200mg a day (roughly one mug of coffee).
- Rest when you need to — fatigue in early pregnancy is real, even if it doesn't show yet.
Frequently Asked Questions
What size is my baby at 5 weeks?
At 5 weeks, your baby is about the size of a sesame seed, typically measuring a few millimetres in length. It's far too early to see this on a standard ultrasound, and an early scan won't usually be booked this soon unless there's a specific medical reason.
When does the baby's heart start beating?
The heart begins forming during week 5 and typically starts its earliest, rapid beats from around week 6, though this can vary slightly. It's usually not reliably visible on an ultrasound until closer to 6-7 weeks, so don't worry if nothing was detected on a very early scan taken around now.
Is it normal to have no symptoms at 5 weeks?
Yes, completely normal. Symptom timing and intensity vary enormously between people and even between different pregnancies for the same person. Some feel fatigue and nausea strongly from very early on, while others notice very little until later — the absence of symptoms this early is not, on its own, a cause for concern.
This article is for informational purposes only and does not constitute medical advice.
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