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5 Weeks Pregnant: Baby's Nervous System Forms & Your First Symptoms Appear

Medically reviewed by

Maryum Sohail, MD Jul 24, 2026

Your baby is the size of a

Sesame seed

Weight difficult to asses

~2 mm / ~0.08 in

Key Takeaways

Your baby is about 2mm long — the size of a sesame seed — and the nervous system, brain and spinal cord are beginning to form, according to the NHS.

A missed period, tender breasts, tiredness and nausea are common early signs — the SOGC lists fatigue, breast changes and nausea among the most common pregnancy symptoms. The NHS notes many women realise they're pregnant around week 5.

Start or continue 400mcg of folic acid every day and book your first prenatal visit — the Public Health Agency of Canada advises continuing folic acid throughout your pregnancy, while the neural tube is forming.

Your Baby at 5 Weeks: Development & Growth

At 5 weeks pregnant, your baby is around 2mm long — about the size of a sesame seed, according to the NHS.

That 2mm is measured crown to rump, which is how fetal length is taken in early pregnancy. Tiny, yes. But this is the week the groundwork is laid — the embryo has folded into a recognisable shape, and the earliest body systems are switching on.

The nervous system is developing first. The NHS states your baby's brain and spinal cord are taking shape this week, forming from the neural tube. That's precisely why folic acid matters so much right now — it helps this structure close properly, offering protection against neural tube defects such as spina bifida. The Society of Obstetricians and Gynaecologists of Canada notes most neural tube defects happen in the first four weeks of pregnancy, often before a woman even knows she's pregnant.

The heart is close behind. The NHS says the tiny heart is starting to form and will beat for the first time around now. The face is also beginning to appear, with a tiny nose and little eyes that stay closed until around 28 weeks. Your baby already has some of its own blood vessels, and a string of them is forming the umbilical cord — while the placenta, being created now, gets ready to deliver oxygen and nutrients.

Your Body at 5 Weeks: Symptoms & Changes

At 5 weeks pregnant, common early signs include a missed period, plus the extreme tiredness, sore breasts and nausea that the Society of Obstetricians and Gynaecologists of Canada lists among the most common symptoms of pregnancy.

Tiredness can hit hard in the first trimester — the Society of Obstetricians and Gynaecologists of Canada lists fatigue among the most common symptoms of pregnancy. Sore breasts and a metallic taste in the mouth are common too. Nausea, often called morning sickness, can start around now, though the Society of Obstetricians and Gynaecologists of Canada notes that even though it's called "morning" sickness, you may feel nauseous at any time of day.

If nausea is arriving, here's the science behind why it varies so much. A 2024 study published in Nature identified GDF15 — a hormone produced largely by the developing placenta — as a key driver of how severe pregnancy nausea and vomiting feel. Higher levels are linked to worse symptoms. That's part of why no two pregnancies feel the same.

Other changes are quieter. The Society of Obstetricians and Gynaecologists of Canada also lists more frequent urination among the common symptoms of pregnancy. The NHS adds a heightened sense of smell, new food likes and dislikes, cravings driven by hormonal changes to taste and smell, a milky white discharge, mild cramping like period pains, and light spotting. Some women feel almost nothing at 5 weeks — and the NHS confirms many won't yet know they're pregnant.

Then there's how you feel emotionally. Finding out you're pregnant can stir up a lot at once, but it's normal to have worries too — the NHS points out that around 1 in 5 mothers feel anxious or stressed during pregnancy. You're not alone in that. If you've been up reading everything at 2am, this calendar is who My Organic Formula made it for — sourced answers, not reassurance that floats. Talk to your doctor or midwife, your partner, or someone you trust rather than carrying it quietly.

What to Do at 5 Weeks Pregnant

NUTRITION AT 5 WEEKS PREGNANT

Fill your plate with folate-rich foods — leafy greens, broccoli, lentils, beans and oranges. The Public Health Agency of Canada notes diet alone isn’t enough to protect against neural tube defects, so these support your supplement rather than replace it.
Avoid liver, liver products and any supplement containing vitamin A (retinol) — the NHS warns too much vitamin A can harm your baby’s development.
If nausea is building, the Society of Obstetricians and Gynaecologists of Canada suggests eating small meals or snacks often so your stomach doesn’t get empty, and trying a few dry crackers.

WHAT SUPPLEMENTS TO TAKE AT 5 WEEKS PREGNANT

Take 400mcg of folic acid every day, continuing throughout your pregnancy — the Public Health Agency of Canada recommends this to help reduce the risk of neural tube defects such as spina bifida. In high-risk women, folic acid reduced the recurrence of neural tube defects by 72%, according to the MRC Vitamin Study (The Lancet, 1991).
Consider a daily 10mcg vitamin D supplement between October and March, when the NHS advises most people cannot make enough from sunlight.

LIFESTYLE TIPS AT 5 WEEKS PREGNANT

Aim for at least 150 minutes of moderate activity that must be spread over at least 3 days a week, which the Society of Obstetricians and Gynaecologists of Canada recommends throughout pregnancy — good options include walking, swimming or gentle stretching.
Do your best to give up alcohol, stop smoking and go easy on caffeine. Once you see a positive test, the Society of Obstetricians and Gynaecologists of Canada (SOGC) advises you to eat well and avoid alcohol, drugs and tobacco — and your doctor or midwife can help you quit. The NHS adds keeping caffeine low from the start.
Book your first prenatal visit now. Once you see a positive test, the SOGC says it’s time to book an appointment with your health care provider, who will start your prenatal care and arrange your first tests.
Look after your emotional wellbeing. If you’re feeling anxious or low, the NHS encourages you to talk to your doctor or midwife — with 1 in 5 mothers affected, support is there for exactly this.

When to Contact Your Doctor or Midwife

Contact your doctor or midwife if you experience:

Any vaginal bleeding — the Society of Obstetricians and Gynaecologists of Canada says to take any vaginal bleeding seriously and contact your health care provider as soon as you notice it, even though about a third of pregnancies have some early bleeding and about half of these continue without further issues.
Nausea and vomiting so severe that you're missing meals, struggling with normal activities or losing weight — the Society of Obstetricians and Gynaecologists of Canada says to see your health care provider if this happens.
Very dark-coloured urine, or not peeing for more than 8 hours, which can signal dehydration from sickness (NHS).
Feeling very weak, dizzy or faint when standing up, tummy pain, a high temperature, or vomiting blood (NHS).
Cravings for non-food items like dirt — the NHS notes this can be pica, caused by a lack of iron, and is worth flagging.
Any concern that's worrying you — your doctor or midwife is there for exactly this.

Questions fréquemment posées

How big is my baby at 5 weeks pregnant?

At 5 weeks pregnant, your baby is around 2mm long — about the size of a sesame seed, according to the NHS. This is a crown-to-rump measurement, the standard way length is taken in early pregnancy. The embryo has taken a recognisable shape, and the nervous system is beginning to form.

What symptoms are normal at 5 weeks pregnant?

Normal symptoms at 5 weeks pregnant include a missed period, extreme tiredness, sore breasts and nausea — the Society of Obstetricians and Gynaecologists of Canada lists fatigue, breast changes and nausea among the most common symptoms of pregnancy. A metallic taste and a heightened sense of smell are also common (NHS). These are driven by early hormonal changes, and symptoms vary widely from woman to woman. Heavy bleeding or severe one-sided pain is not typical and warrants a call to your doctor or midwife.

Is it normal to have no symptoms at 5 weeks pregnant?

Yes, it’s completely normal to feel few or no symptoms at 5 weeks pregnant. The Society of Obstetricians and Gynaecologists of Canada notes that some women sail through pregnancy with very few symptoms, while others have multiple discomforts. The absence of symptoms doesn’t mean anything is wrong — hormone levels and sensitivity differ for everyone, and symptoms often appear over the following weeks.

When should I take a pregnancy test at 5 weeks pregnant?

Now is a good time to take a pregnancy test. The Society of Obstetricians and Gynaecologists of Canada (SOGC) advises that the easiest approach is to wait until you have missed a period and then test, because testing your urine too soon may give a negative result when you are actually pregnant. Week 5 is when many women notice a late period. If you get a positive result, it’s time to book an appointment with your doctor or midwife to start your prenatal care.

Is spotting normal at 5 weeks pregnant?

Light spotting is common at 5 weeks pregnant and can sometimes be implantation bleeding, which happens as the embryo attaches to the lining of the womb. However, because any early bleeding can also indicate a complication, it should always be reported to a doctor or midwife.

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