Mother and Baby

3 weeks pregnant: advice, symptoms and what to expect

Section: Week by Week
3 weeks pregnant

At three weeks pregnant, it is time for the sperm to meet the egg. As we mentioned in week two, your partner’s sperm goes on a very difficult journey to fertilise your egg, but if it’s made it and you’ve conceived, this is the week when your baby will first start to form.

At week three, you're in the first month of your pregnancy and you still have eight months to go until you can meet your little baby! 

Week three pregnancy

In this article:

How big is my baby at three weeks pregnant?

Right now, your baby is a ball of around 100 cells about the size of a pinhead. This is officially referred to as a blastocyst.

Baby the size of a pin head at three weeks

Common symptoms to look out for:

What symptoms do you need to look out for and what advice is helpful at this stage?

Expand Image

1) A heightened sense of smell

Changes to your sense of smell are a side effect of oestrogen.

If you find like every little fragrance around you has been magnified, this could be an early sign that your body is getting ready for a baby.

This may cause morning sickness in the next few weeks, so you might want to think about switching to unscented toiletries.
Expand Image

2) Abdominal pressure

Don’t worry, a feeling of pressure or even the feeling of period cramps without the bleeding is nothing to panic about.

You might be feeling the sensation of embryo implantation, an increased blood flow to this area or even the thickening of your uterus. If you’re worried, we recommend you book an appointment with your GP.
Expand Image

3) Metallic taste

A common side effect of pregnancy is a metallic taste, caused by the changing hormones in your body.

These side effects will usually settle in the second trimester, although this can feel a long way away right now, so try sipping lemonade and other citrus juices to try and help.
Expand Image

4) Nausea

As the pregnancy hormone hCG appears in your body you may feel queasy or nausea or even be sick. If you are suffering with morning sickness already, there's a chance you could be further a long than you thought.
Expand Image

5) Implantation bleeding

If your little soon-to-be-embryo has already made it to his or her new home, you may see a bit of spotting as the fertilized egg burrows into the wall of your uterus.

There are certain ways you can tell the difference between implantation bleeding and a period.
Expand Image

6) Missed period

If you often find your cycle is shorter than the standard 28 days, you may realise by the end of this week that you have missed a period. If this is the case, it's time to take a pregnancy test.
Expand Image

7) Positive home pregnancy test

Certain pregnancy tests are better suited to detecting early pregnancies so make sure to check the box. 

The amount of pregnancy hormone hCG in your body may not yet be high enough for a pregnancy test to detect it.

However, the hormone doubles every 48 hours and if you get a negative result you can always take a second a few days later.

What is my baby doing?

Within hours of being fertilised, your tiny egg will start to travel from your fallopian tube to your uterus, and the fertilised egg (now medically referred to as the zygote) will divide into 16 identical cells.

This journey can take up to six days, so implantation probably won’t happen until week four.

The inside of the cell mass will become the embryo itself and the amniotic sac. The outer cell mass will become the placenta.

What's happening in my body?

Body at three weeks pregnant From the outside, it probably won’t feel like much is happening right now, but if you’ve timed things right, that precious blastocyst is starting out on its journey and heading for your uterus.

Just after the egg is released from the follicle it came from, it will be replaced by a yellow group of cells called the corpus luteum.

This, in turn, produces enough of the pregnancy hormones progesterone and oestrogen, to support your future baby for the next ten weeks, until the placenta is ready to take over.

At this point, you still probably won’t get a positive pregnancy test, but in the next few weeks, once the blastocyst has made its way into the uterus, the cells of the developing placenta will make human chorionic gonadotropin (hCG).

This surges in your first trimester and tells your ovaries to stop producing eggs and start making more progesterone and oestrogen.

What should I be doing at this stage?

Healthy balanced diet at three weeks pregnantYou need to make sure you are eating healthily and getting the right nutrients and vitamins when trying to conceive or during the early stages of pregnancy.

Up the protein: Your baby will need extra protein to help it grow, so try and make sure you get three servings of protein a day in these first few weeks.

Make sure you’re getting enough calcium: It might seem obvious, but if you’re not getting enough calcium in your diet when you’re pregnant, your baby will start taking it from your bones!

Now’s the time to up the intake – foods like Greek or frozen yoghurt will help. If you’re still struggling, it might be worth looking for a calcium supplement

Read more: Your go-to guide to taking supplements while pregnant

Things to think about this week...

Happy mum at three weeks pregnant Work out your due date: If you're having trouble working it out on your fingers, try out our due date calculator.

All you need to know is the first day of your last period and how many days your menstrual cycle is!

Educate yourself! It's time to start reading all about what to expect in your first trimester. You'll find out what your body and your baby will be doing in the next 12 weeks!

Keep taking your vitamins: Taking prenatal vitamins will benefit your baby's development and nourish your pregnancy body and health. 

  • Did you notice any of these changes at three weeks pregnant? Let us know on Facebook or Twitter and make sure you're following Mother & Baby on Instagram for relatable memes, inspiring stories and parenting hacks!
  • Go forward to four weeks pregnant 
  • Go back to two weeks pregnant 
  • Have approx 60 seconds to spare? Why not join thousands of mums-to-be and start your very own Amazon baby wish list! They're absolutely free to create and perfect to send to the friends, aunties and your mum to make sure you're getting the baby products you really here!
  • Author: Lorna White Lorna White
  • Job Title: Digital Writer

Lorna is the digital executive and regular contributor for Mother&Baby. After running the Yours magazine website which specialises in content about caring for kids and grandchildren, she has now brought her expertise to the UK's #1 leading pregnancy and parenting magazine. Lorna specialises on a range of topics from potty training and nutrition, to everything and anything that will keep your tot occupied!