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Week 4 of Pregnancy

Written by Amina Hatia RM
Medically reviewed by Marley Hall BA RM Diphe
November 25, 2021

Congratulations! You are pregnant and if you’ve just arrived here, it’s most likely you’ve only just found out!  How exciting and daunting and overwhelming at the same time.  If you’ve been following us from week 1, then you know that your baby – although absolutely tiny, is developing and growing.

What happens in week 4 of pregnancy

You may have had an official confirmation of your pregnancy – even if you had an inkling before. It’s probably now in week four where you have carried out a pregnancy test and got a positive result!

Pregnancy tests are often used from the day when you think your period should’ve begun, although nowadays there are very sensitive early pregnancy tests that you can buy to use before you miss a period, in some cases they can detect a pregnancy from as early as 8 days after you’ve conceived.

Pregnancy tests work by detecting a hormone in your urine called human chorionic gonadotrophin (hCG) that is produced about 6 days after fertilisation has happened.  

You’ve probably already carried the test out by peeing on a pregnancy stick and then that arduous wait for the result to appear – feels like forever doesn’t it, even though it’s only a few minutes!  

Whilst it may feel strange to be testing at home and this being your only confirmation of pregnancy, remember that home pregnancy tests have evolved a lot and are very reliable and accurate so long as you follow the instructions!  Similarly, a positive test result means exactly that – you are pregnant, it is very rare to get a false positive result.

Week 4 pregnancy symptoms

You may now start to feel some of those early pregnancy symptoms – or not at all.  It can be hard to have had a positive pregnancy test and not have any symptoms at all but try not to worry – some people don’t get any at all and a lack of pregnancy symptoms is not an indication of anything being wrong at this stage.


Some of the symptoms like bloating may be going unnoticed or have been there from week 3 – bloating is caused by pregnancy hormones so it’s a common symptom.  

Light Bleeding (Spotting)

You may also experience some very light bleeding or what is often called spotting – exactly that – spots of blood from the vagina. If this happens, it can be worrying but often at this stage is caused by your baby implanting (think burrowing) into the uterus which is referred to as implantation bleeding. If this happens to you, do let your GP know and update them if the bleeding becomes heavier or is accompanied by pain.

Sore Breasts

Sore breasts are another common sign – and often the first indication of pregnancy. Despite it being very early in your pregnancy and your baby being tiny, your breasts are already getting ready for the important job of breastfeeding. The soreness happens because as your pregnancy hormones increase, your milk ducts begin to swell too.


Tiredness is something that almost everyone talks about in early pregnancy – it’s a tiredness like no other and leaves you feeling completely exhausted.  For the next few weeks your body is working super hard at building a whole new human being and this means you are left feeling so tired.

Need for supplements

You’re also probably now wondering what you need to do and who to tell you are pregnant! Well start off by taking (if you haven’t already been) supplements of folic acid – for most pregnant women this will be 400mcgs a day, but some of you may need a higher dose that only your GP can prescribe. 

Check with your GP if you need a higher dose – and at the same time let them know you are pregnant and would like to be referred for antenatal care. 

You may also be able to do this yourself – many hospitals have the option to self-refer online – so check if that is possible.

It is also important to take vitamin D alongside your folic acid – this should be 10 mcg a day and you can buy it from your local chemist or even supermarket.

Also have a check of our blog page on advice of what food to avoid now you are pregnant and what to be cautious about – it’s not many things, but important you are aware to avoid the foods and drinks that may have an impact on your pregnancy or baby’s development.

The same applies for alcohol and smoking – giving up both in pregnancy is the best way of protecting your baby’s health and supporting their development.’

How big is my baby?

Still tiny – but growing and doing amazing things! Your baby measures around 2mm, so around the size of a poppy seed – yes, babies are almost always described in food size details for some reason!

Despite being miniscule – things are changing fast.  By now your baby (called an embryo at this stage) has comfortably embedded into your uterus, and the baby’s heart and nervous system are starting to develop. At the moment, your baby is getting their nourishment and energy from what is called a yolk sac, however, soon the placenta will take over this role. 

Week 4 pregnancy tips

What can I do this week?

  • Take it easy – if you are feeling tired, rest as much as you can
  • Make sure you are taking the right dose of folic acid by checking with your GP
  • Let your maternity unit in your local hospital know you are pregnant – either by self-referring online or asking your GP to start taking vitamin D
  • Breathe – it’s the beginning of a wonderful new journey