6 Weeks Pregnant: Baby Development

By six weeks pregnant, your baby has grown from a microscopic cluster of cells into a recognisable embryo with a beating heart and the earliest beginnings of a face, a brain, and limbs. It is an extraordinary week of development. Here is a detailed look at what is happening and what you might expect at this stage.

Baby Size at 6 Weeks
The Heartbeat
Development Milestones
The Brain and Nervous System
What You Might Be Feeling
Scans at 6 Weeks
When to Seek Help
Frequently Asked Questions

Baby Size at 6 Weeks

Your embryo is now roughly the size of a lentil — around 4 to 5 mm from crown to rump. That is still very small, but it represents a dramatic increase from just two weeks ago when the embryo was barely visible. Growth at this stage is extraordinarily rapid, with the embryo almost doubling in size week on week throughout the first trimester.

The Heartbeat

One of the most significant milestones at six weeks is the beginning of cardiac activity. The primitive heart — at this stage essentially a tube of muscle — begins contracting and can produce a flickering movement visible on transvaginal ultrasound. This is sometimes described as a "heartbeat," though at this stage it is not yet the fully formed four-chambered heart that will develop over the coming weeks.

The heart rate at six weeks is typically faster than you might expect — often between 90 and 110 beats per minute, rising to around 160 to 180 beats per minute by the end of the first trimester. This rapid rate is entirely normal for an embryo at this stage of development.

It is worth knowing that cardiac activity is not always detectable at exactly six weeks. The visibility of a heartbeat at this stage depends on the precision of your gestational age, the equipment used, and individual variation. If you have an early scan and cardiac activity is not seen at six weeks, this does not automatically indicate a problem — a follow-up scan is usually recommended a week or so later to check progress.

Development Milestones

Six weeks is a busy time developmentally. Alongside the heart, several other structures are taking shape:

Limb buds — small paddle-like protrusions are beginning to appear where your baby's arms and legs will develop. These are not yet recognisable as limbs, but the foundations are being laid.
Facial features — the optic vesicles (which become the eyes) and the otic pits (which become the ears) are forming. The face is beginning to take shape, though it will be many more weeks before it looks anything like a recognisable baby face.
The head — the head is disproportionately large at this stage relative to the body, reflecting how rapidly the brain is developing.
The tail — embryos at this stage have a small tail-like structure at the base of the spine. This is a normal part of development and disappears over the coming weeks.
The gut — the digestive tract is beginning to form, with the stomach and intestines taking their earliest shape.
The lungs — lung buds are present at six weeks, though the lungs will not be functional for many more months.

The Brain and Nervous System

The neural tube, which began closing in week four, has now sealed. From it, the three primary regions of the brain — the forebrain, midbrain, and hindbrain — are differentiating and growing rapidly. The nervous system is developing at a remarkable pace, with neurons beginning to form and connect. This is one of the reasons that adequate folic acid in early pregnancy is so important: it supports healthy neural tube closure and brain development.

By six weeks the embryo's brain is already sending signals, though these do not yet result in conscious movement or sensation. The foundations being laid now will support everything from your baby's ability to move in the womb to their learning and development after birth.

What You Might Be Feeling

By six weeks, pregnancy symptoms are typically becoming more noticeable if they haven't already. Many people find this is when nausea — commonly called morning sickness, though it can happen at any time of day — begins in earnest. Other common experiences include:

Significant tiredness and fatigue
Breast tenderness and fullness
Frequent urination as the uterus grows and presses on the bladder
Heightened sense of smell
Food aversions or cravings
Mild pelvic cramping or a feeling of heaviness
Bloating and constipation
Emotional sensitivity or mood changes

If you have not already contacted your GP, do so now to be referred for your midwife booking appointment, which usually takes place between eight and twelve weeks.

Scans at 6 Weeks

In the UK, routine NHS scans do not begin until around 8 to 12 weeks (the dating scan). A six-week scan is not part of standard NHS antenatal care, but some people have one arranged through their Early Pregnancy Unit (EPU) if they have experienced bleeding, pain, or a history of pregnancy loss.

At six weeks, a transvaginal ultrasound can usually show a gestational sac and yolk sac, and may show early cardiac activity. An abdominal scan at this stage is less likely to show clear detail. If you are offered or are considering a private early scan, be prepared for the possibility that the results may not be fully conclusive and a follow-up scan may be recommended.

Seeing the heartbeat at an early scan can be very reassuring, particularly if you have previously experienced pregnancy loss. However, it is important to understand that a heartbeat seen at six weeks does not guarantee the outcome of the pregnancy — it is a positive sign, but early pregnancy loss can still occur even after cardiac activity has been detected.

When to Seek Help

Most early pregnancy symptoms at six weeks are entirely normal. However, contact your GP, midwife, or Early Pregnancy Unit if you experience:

Bleeding that is heavier than light spotting, or bright red bleeding
Severe one-sided abdominal or pelvic pain
Shoulder tip pain, which can occasionally signal internal bleeding from an ectopic pregnancy
Vomiting so severe that you cannot keep any fluids down (this may indicate hyperemesis gravidarum, which can require treatment)
Feeling faint, very unwell, or any symptoms that worry you

If you are unsure whether your symptoms need assessment, call NHS 111 for guidance. For severe pain or heavy bleeding, call 999 or go to your nearest A&E.

Frequently Asked Questions

### How big is my baby at 6 weeks?

Your embryo is approximately the size of a lentil, around 4 to 5 mm from crown to rump. Growth is rapid at this stage and your baby will be noticeably larger by next week.

Can I see my baby on a scan at 6 weeks?

A transvaginal scan at six weeks can usually show the gestational sac and yolk sac, and may detect early cardiac activity (a flickering heartbeat). Not all pregnancies show a heartbeat at exactly six weeks — this depends on how accurately your gestational age has been calculated and individual variation. If no heartbeat is seen, a follow-up scan in one to two weeks is standard practice before any conclusions are drawn.

Is it normal not to have symptoms at 6 weeks?

Yes, symptom experiences vary widely between people and between pregnancies. Some feel significant nausea and fatigue by six weeks; others feel very little at all. The absence of symptoms does not indicate a problem with the pregnancy. If symptoms that were present suddenly disappear, it is worth mentioning to your GP or midwife, but even this is often a normal variation rather than a sign of concern.

Always speak to your midwife or GP for personalised advice about your pregnancy.