At 6 weeks the embryo is about 4 mm — lentil-sized — and its heart is beating fast enough to be picked up on a transvaginal scan. This is also the week the neural tube finishes closing, and the week most women start to feel genuinely pregnant.
The short answer: cardiac activity is usually detectable from around 6 weeks at 100–120 beats per minute, though dating being a few days out is common and a repeat scan is the normal next step rather than a worry. Limb buds, eye spots and ear pits appear. Nausea, exhaustion and sore breasts typically arrive now. Avoid anything that raises your core temperature — hot tubs, saunas, very hot baths — while the neural tube completes.
Your baby this week
The heart has divided into chambers and is beating at roughly 100–120 beats per minute — it will climb over the next few weeks before settling into its normal range. Blood is circulating through a body that is still curved like a comma.
On the head, dark spots mark where the eyes are forming and small depressions mark the future ears. The jaw, chin and cheeks are taking shape. Along the sides of the body, limb buds appear — small paddles that will become arms and legs, with the arm buds slightly ahead of the legs.
Inside, the neural tube completes its closure, and the brain begins dividing into its three main regions. The first synapses — connections between nerve cells — start to form. The yolk sac is still doing the job of making blood cells, and will hand that over to the liver over the coming weeks.
Your body this week
The uterus is now about the size of a tennis ball, and increased blood flow to the pelvis can give a feeling of heaviness or fullness low down. Your kidneys and liver are already working harder, processing waste for two.
Nausea is usually well established by now, and despite the name it is not confined to mornings. It tends to be worst when your stomach is empty, which is why eating small amounts frequently works better than three meals — including something plain before you get out of bed. Our morning sickness guide covers the evidence for ginger, vitamin B6 and the point at which medication is appropriate.
Exhaustion in the first trimester is driven by progesterone and is often the symptom women find hardest to explain to other people. It is not laziness and it does not respond to willpower. It usually lifts noticeably in the second trimester.
Tests and appointments
If you have not booked your first antenatal appointment, do it now — it is normally held between 8 and 12 weeks. An early scan may be offered if you have had an ectopic pregnancy or recurrent miscarriage, conceived through IVF, or have pain or bleeding. It is also worth asking about a ferritin test: ferritin reflects your actual iron stores, and a normal haemoglobin can sit on top of depleted stores.
✅ Worth doing this week
- Skip hot tubs, saunas and very hot baths — raising core temperature in the first trimester is the specific concern, not warmth in general
- Eat 5–6 small meals rather than three; stable blood sugar reduces nausea measurably
- Keep something plain by the bed — dry crackers before you sit up help more than they should
- Ask about a ferritin test at your booking appointment rather than only a full blood count
- Treat a fever, do not wait it out — paracetamol is the usual choice, and NSAIDs are not
When to call your doctor
Call the same day if: you have bleeding heavier than spotting, severe or one-sided abdominal pain, shoulder-tip pain, dizziness or fainting, a temperature above 38°C, or you cannot keep fluids down for 24 hours. Severe one-sided pain between weeks 5 and 10 is the classic timing for an ectopic pregnancy and needs urgent assessment.
FAQ — 6 weeks pregnant
Can you see a heartbeat at 6 weeks?
Often, yes — a transvaginal scan can usually detect cardiac activity from around 6 weeks, at roughly 100–120 beats per minute at this stage. But dating is commonly a few days out, so not seeing one at 6 weeks is frequently just timing. The standard response is a repeat scan in 7–10 days rather than any conclusion drawn on the day.
How big is the baby at 6 weeks?
About 4 mm crown to rump — roughly a lentil. The embryo is curved, with dark spots where the eyes are forming, small pits for the ears, and paddle-like buds that will become arms and legs.
Why should I avoid hot baths and saunas at 6 weeks?
Raising your core body temperature in the first trimester — a hot tub, sauna, or a long very hot bath — has been associated with an increased risk of neural tube defects, and the neural tube is completing its closure right about now. A warm shower or a comfortably warm bath is fine; the concern is prolonged immersion hot enough to raise core temperature. A fever should also be treated rather than left, which is a reason to call your doctor rather than wait it out.
Is it normal to have no symptoms at 6 weeks?
Yes. Symptom intensity varies enormously and is not a measure of how a pregnancy is progressing — plenty of women feel almost nothing at 6 weeks and go on to have entirely uneventful pregnancies. It is also common for symptoms to come and go day to day. A sudden, complete disappearance of symptoms alongside bleeding or pain is worth mentioning to your doctor, but symptoms fluctuating on their own is not.
Week 6 at a glance
At 6 weeks the embryo is about 4 mm and the heart, now chambered, beats at roughly 100–120 beats per minute — usually visible on a transvaginal scan, though dating being a few days out is common enough that a repeat scan is routine rather than ominous. Limb buds, eye spots and ear pits appear, and the neural tube finishes closing. For you, nausea and exhaustion are typically at their most noticeable, the uterus has reached tennis-ball size, and the one specific thing to avoid is anything that raises core body temperature while the neural tube completes.
Inside Baby Novum: the symptom journal records nausea severity day by day, which turns "I have felt awful for weeks" into a chart a doctor can act on. The safe foods guide rates 240 foods by trimester, offline, for the weeks when nothing sounds edible.