Pregnancy Week 5: Your Baby's Heart Begins to Beat

8 min read

Quick answer: At week 5 your baby is about the size of a sesame seed, around 2mm long, and the heart is beginning to form and may already be starting to beat, though it is far too early to detect on a scan. Contact your GP to confirm your pregnancy, take 400mcg of folic acid daily until 12 weeks, and stop drinking alcohol.

What parents need to know

Welcome to week 5 of your pregnancy. If you've just confirmed the news with a positive test, you may be feeling a wonderful mix of excitement and nerves, and perhaps the first stirrings of nausea. This week is a pivotal one: tiny but extraordinary things are happening inside you.

Baby's size	About a sesame seed, around 2mm long
Folic acid	400mcg daily until 12 weeks pregnant
Vitamin D	10mcg daily from October to March (all year for some)
Caffeine limit	No more than 200mg per day
Booking appointment	Usually between 8 and 10 weeks

How big is your baby at 5 weeks?

Your baby is about the size of a sesame seed, around 2mm long. At this stage, your baby is called an embryo. Small as that sounds, this tiny cluster of cells is already hard at work laying the foundations for an entire human being.

What's happening with your baby?

Week 5 is one of the most significant weeks in early development. The three primary layers of the embryo are forming, and each will eventually become different parts of your baby's body. The outer layer (ectoderm) will become the skin, hair, brain, and nervous system. The middle layer (mesoderm) will form the heart, muscles, and skeleton. The inner layer (endoderm) will eventually develop into the digestive system and lungs.

Perhaps the most exciting development this week is that your baby's heart is beginning to form and may already be starting to beat — though it's far too early to detect on a scan. The neural tube, which will become your baby's brain and spinal cord, is also starting to close. This is precisely why folic acid is so important right now, as it helps prevent neural tube defects such as spina bifida.

Close-up of baby feet on a textured white blanket, evoking warmth and innocence.

What's happening in your body?

By week 5, your period is late, and a pregnancy test will show a clear positive result. The hormone human chorionic gonadotropin (hCG) is being produced in increasing quantities by the developing placenta: this is what causes the test line to appear and what drives many of your early pregnancy symptoms.

Common symptoms at week 5 include breast tenderness (your breasts may feel heavier or more sensitive than usual), unusual fatigue as your body works hard to nurture your growing baby, and the beginnings of nausea or morning sickness, which often peaks between weeks 8 and 10. Some women also notice they need to wee more frequently, and mood changes are common thanks to shifting hormone levels. Not everyone experiences noticeable symptoms this early, and that's perfectly normal too: every pregnancy is different.

Important steps to take this week

Contact your GP

In the UK, your first step is to contact your GP surgery to confirm your pregnancy. Your GP will then refer you to a midwife for your booking appointment, which usually takes place between 8 and 10 weeks. Don't delay getting in touch: antenatal appointment slots can fill up, and you'll want plenty of time to register.

Start or continue folic acid

The NHS recommends taking 400 micrograms (mcg) of folic acid every day until you are 12 weeks pregnant. Folic acid significantly reduces the risk of neural tube defects. If you have conditions such as diabetes or epilepsy, or if there's a family history of neural tube defects, your GP may recommend a higher dose of 5mg daily — so do check with them. Vitamin D (10mcg daily) is also recommended between early October and late March, and all year if you usually cover most of your skin outside or spend a lot of time indoors. Consider taking it all year if you have black or brown skin.

Stop drinking alcohol

The NHS advises that no amount of alcohol is considered safe during pregnancy. Now is the time to stop completely if you haven't already. You should also reduce your caffeine intake to no more than 200mg per day — for example, a cup of instant coffee has about 100mg and a cup of tea about 75mg (filter coffee and coffee from coffee shops can contain more).

Eat well and listen to your body

If nausea is starting, eating little and often can help enormously. Plain crackers, ginger biscuits, or bland foods are often easier to manage. Cold foods are sometimes better tolerated than hot ones. Staying hydrated is important: try sipping water steadily throughout the day rather than drinking large amounts at once. If you're struggling to keep anything down, speak to your midwife or GP.

When to get help

Some symptoms in pregnancy can be a sign of something serious and need checking quickly. This is who to contact, and how soon.

Call 999 if:

you're bleeding from your vagina and the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe pain in your tummy, pain in your shoulder, or feel sick, faint, dizzy or lose consciousness
you have a sharp, sudden and intense pain in your tummy together with feeling very dizzy or fainting, feeling sick or looking very pale, as this could mean an ectopic pregnancy has ruptured (you can also go straight to A&E)
you have severe difficulty breathing (you're gasping, choking or not able to get words out) or your chest feels tight or heavy
you have pain and swelling in one leg and you also feel short of breath or have chest pain. A blood clot in the leg can travel to your lungs, which can be life-threatening
you have possible signs of sepsis, such as breathing very fast, being confused or having slurred speech, blue, pale or blotchy skin, a rash that does not fade when you press it, or a very high or very low temperature. Being pregnant makes sepsis more likely
you do not feel you can keep yourself safe (a mental health emergency is as serious as a physical one)

Always call 999 if you think it's a life-threatening emergency, no matter what stage of pregnancy you are.

Contact your GP or early pregnancy unit right away if:

you have light bleeding or spotting, even if you have no pain or only mild tummy pain
you have vaginal discharge that's unusual for you, or fluid leaking from your vagina
you have tummy pain low down on one side, or pain in the tip of your shoulder (where your shoulder ends and your arm begins). Symptoms of an ectopic pregnancy usually start between 4 and 12 weeks, so get advice right away, even if you have not had a positive pregnancy test yet
you have stomach pain that is severe or does not go away after you've rested for 30 to 60 minutes, or stomach pain with regular cramping or tightenings, lower back pain, or pain when you pee
your breathlessness comes on suddenly, you're out of breath when you're lying down, or you're breathless and also have chest pain or feel dizzy
you have pain or swelling in one leg, usually in the calf or thigh. This could be a blood clot (deep vein thrombosis, or DVT), which is more likely when you're pregnant
you have a high temperature (38C or above), or you feel hotter than usual or shivery. A high temperature can be a sign of an infection, so it's important to get it checked

Also contact your GP or early pregnancy unit right away if you have tummy pain and you need to pee suddenly or more often than usual, or your pee looks cloudy, pink, red or brown. Pain when you pee, pain or pressure in your bottom when you poo, or diarrhoea can also be signs of an ectopic pregnancy, so get medical advice if you have any of these.

If you cannot reach them, or you're not sure what to do, call NHS 111.

Speak to your GP or midwife if:

you're worried about your mental health, or stress, anxiety or low mood are affecting your day-to-day life. If you need urgent help for your mental health, call 111 and select the mental health option, or ask for an urgent GP appointment

Your week 5 checklist

Simple steps for week 5 of your pregnancy

This week, aim to:

Contact your GP surgery to confirm your pregnancy.
Start or continue taking 400mcg of folic acid and 10mcg of vitamin D daily.
Stop drinking alcohol and reduce caffeine to under 200mg per day.
Eat small, regular meals and stay hydrated.
Make a note of any symptoms to discuss at your booking appointment.

Sources: NHS, Tommy's, NCT. General information, not medical advice.

Sources & further reading

General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.