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Pregnancy weeks:

3 weeks pregnant: Baby’s development, symptoms and tips

Three weeks into your pregnancy and this is where the magic really begins. As pregnancy is dated from the first day of your last period, the first two weeks of pregnancy are odd in that you’re not technically growing a baby just yet – only preparing the ground.

Conception typically happens in the third or fourth week, so at three weeks pregnant, your tiny egg could meet an equally tiny sperm and fertilization will take place. Congratulations!

Implantation during week 3

In this week, the fertilised egg will burrow into the lining of the uterus (womb) in a process called implantation. This usually occurs about 5 – 6 days after ovulation, so it may fall into the fourth week of your pregnancy depending on your cycle.

Implantation can come with some symptoms, including light bleeding and abdominal cramps. For some people, this can be really noticeable, but other people will not feel anything at all as their baby gets comfy in its new home.

Baby’s development at 3 weeks – how big is my baby?

There is not yet a foetus at 3 weeks, as the cells that make up your growing baby are still so small and in such an early stage of development that they are not even quite an embryo yet. If you were to try a regular ultrasound scan at this point, there would be nothing much to see and no heartbeat to detect. However, there is lots going on during this point of the first trimester, as the main structures of the body and organs begin to form.

Positive pregnancy test – week 3

It is possible to test positive in the third week of pregnancy, as your body starts producing the hormone Human Chorionic Gonadotrophin (HCG), which stops you from having a period and shows in your urine – this is what home pregnancy testing kits can detect when you miss your first period.

However, if you have arrived at this page after doing a pregnancy test that tells you you’re 3 weeks pregnant, you might be further along than you think. Those tests date from the point of conception, so you can probably add two weeks or even more . Check the individual brands’ instructions.

You can check our due date calculator to work out when your baby is due.

Pregnancy symptoms at 3 weeks

The most likely symptoms this week will relate to ovulation and implantation. All the dramatic body changes are happening on a very small scale inside your fallopian tubes and womb. You can expect your usual symptoms of ovulation, alongside possible light bleeding from the implantation and cramps. Implantation bleeding is usually brown or pink spots on wiping, not fresh, bright red blood.

As the HCG hormone starts to be produced, you may also get some more typical pregnancy symptoms, like tiredness and nausea – but most likely this won’t start for another few weeks.

How you can help your body at the beginning of your pregnancy

A balanced diet is crucial in order for the egg to grow as it should. Make sure you get plenty of vitamins – and remember that some vitamins are fat-soluble, which means that fats are required for their absorption and processing within the body. 

We don’t just get fats from meat: cheese, milk, butter and other dairy products contain fats, as do oils. Fats don’t necessarily have to come from animals either. Vegetable fatty acids are unsaturated, making them more digestible for our metabolism (plus there are lots of creative ways to use them when cooking!). 

Eat fresh food as much as possible and enjoy everything nature has to offer. Try to avoid processed food and make raw fruit and vegetables a frequent part of your diet, as these are good sources of vitamins which will help your body cope with pregnancy. Fruit and vegetables also contain high amounts of fibre, which will become increasingly important as your pregnancy progresses.

Midwife’s advice

‘In the early stage of pregnancy, many women want to eat big, hearty meals. Don’t worry, your little Peanut will survive. This stage will pass, and then you can start to eat more healthily again.’ Dorothee Kutz, midwife

Food containing plenty of iron and folic acid (a vitamin which plays a major role in blood formation and cell growth) is particularly recommended. Pregnant women need a lot of folic acid, as it also helps avoid developmental disorders in their unborn baby.

However, folic acid is extremely sensitive, so getting enough of it in your diet during pregnancy is almost impossible. As a result, we recommend that you start taking special dietary supplements (usually in combination with iodine) from the moment you decide you want to try for a baby. Speak to your doctor or midwife about the supplement that’s right for you!

Iron transports the all-important oxygen in our blood. As pregnant women are feeding both themselves and their unborn baby, they need large amounts of iron and have regular check-ups where their blood is taken to measure its iron levels.

What you should definitely avoid

If you’re pregnant, there are certain things you should avoid as they will impair your child’s healthy development and your personal wellbeing.

  • Alcohol:

Alcohol weakens your body, particularly if you consume it regularly. It has also been shown to impede a baby’s development. Each mouthful of alcohol will reach your baby, as it passes straight through the placenta.

  • Nicotine:

Nicotine increases your heart rate and makes your body stressed. It can quickly lead to an addiction, which is not compatible with a healthy pregnancy. It enters the bloodstream, so it reaches the developing uterus lining (which receives a rich supply of blood and can therefore contain all kinds of toxins). Nicotine can result in insufficient intrauterine blood flow, which will impair your child’s development.

  • Stress:

If you know for sure that you’re pregnant, you should avoid stress as much as possible. Even working in day and night shifts can disrupt your body’s natural rhythm in a small way, which can have a damaging effect on your baby’s development.

Midwife’s advice

‘Some women don’t know that they’re pregnant right at the start, and they might drink alcohol or smoke. Don’t feel guilty about it. The “all or nothing” principle still applies: either the pregnancy will last, or unfortunately it won’t. However, this may then be due to other reasons. As soon as you know that you’re pregnant, you should, of course, stop smoking and avoid alcohol.’ Dorothee Kutz, midwife

Top tips

  • Keep calm if you think you might be pregnant.
  • Buy a reliable pregnancy test.
  • Make an appointment with your gynaecologist.
  • Talk to someone you trust about how you’re feeling.


Questions you may want to ask your doctor or midwife

Getting sufficient vitamins and minerals

Particularly at the beginning of pregnancy, there is a risk of your baby developing deformities as a result of deficiencies.  One example is neural tube defects, which are caused by the expectant mother not getting enough folic acid, a substance which is crucial for generating fresh cells. For this reason, supplements containing folic acid are recommended if you’re trying for a baby or are pregnant. Early on in your pregnancy, you’ll need 400 micrograms a day, considerably more than the 300 micrograms needed by a woman who is not pregnant. From week 12, your daily folic acid requirements will increase to up to 800 micrograms.

Many supplements that contain folic acid also contain iodine. If you have thyroid disease or a hormonal imbalance in your thyroid gland, iodine is not recommended and you should take a supplement that does not contain iodine.

The best thing to do is to discuss your personal circumstances with your doctor or midwife. 

Information about the reviewer:

Marley Hall is a UK-registered, award-winning midwife, educator and author from Surrey. Qualified in 2009, Marley now works as a private independent midwife and is one of the founding members of NowBaby Live. She is a mother of 5 and is passionate about ensuring women and their partners are given informed choices. Find out more here.