3 Weeks Pregnant: Fertilisation, Implantation & Early Signs

3 Weeks Pregnant: Fertilisation, Implantation & Early Signs

At 3 weeks pregnant, fertilisation has usually just happened. The fertilised egg is dividing into a tiny ball of cells as it travels down the fallopian tube to your uterus, where it starts to implant. Most people don't notice anything yet, and it's still too early for a pregnancy test.

Baby's size
Smaller than a grain of salt
What's happening
Fertilisation and the start of implantation
Can I test yet?
Not yet. Wait until your period is due, around the end of week 4
Keep taking
Folic acid and iodine

What's happening this week

This week, a single fertilised egg makes its way to your uterus and starts to settle in. Days are counted from fertilisation.

  1. FertilisationAround ovulation

    Sperm meets the egg in the fallopian tube. Your baby's genetic make-up, including their sex, is set at this moment.

  2. Cell divisionDays 1 to 3

    The fertilised egg divides again and again as it moves slowly along the fallopian tube.

  3. Arriving in the uterusDays 4 to 5

    It's now a hollow ball of cells called a blastocyst, only about 0.1 to 0.2 millimetres across.

  4. Implantation beginsAround days 6 to 10

    The blastocyst burrows into the lining of your uterus and starts making hCG, the hormone pregnancy tests look for. This often carries on into week 4.

The outer cells of the blastocyst will go on to form the placenta. Until the placenta takes over at around weeks 10 to 12, hormones from your ovary, including progesterone, keep the lining of your uterus thick and supportive.

Early signs at 3 weeks pregnant

Most people don't notice any signs this early, and many of the ones that do appear feel a lot like PMS. You might notice:

  • Light spotting. Implantation bleeding is usually pink or brown, lasts a day or two and is much lighter than a period.
  • Mild cramping. A light pulling or pressure low in your tummy.
  • Bloating. Rising progesterone slows digestion, which can leave you feeling puffy.
  • Tender breasts. Hormone changes can make them feel sore or full.
  • A stronger sense of smell. Everyday smells may suddenly seem much stronger.

See your GP or go to your nearest emergency department if you have heavy bleeding, strong pain on one side of your tummy, shoulder tip pain, or feel faint.

When can I take a pregnancy test?

Home pregnancy tests detect hCG, which your body only starts making once implantation begins. Levels are too low to show up this week for most people. For the most reliable result, test from the day your period is due, around the end of week 4. If your test is negative and your period still doesn't come, test again in a few days. A blood test from your GP can pick up a pregnancy a little earlier.

Work out your due date

Looking after yourself this week

Keep up folic acid and iodine

These early weeks are when folic acid matters most for your baby's developing brain and spine. Keep taking 400 micrograms of folic acid and 150 micrograms of iodine a day, unless your GP has recommended a different dose.

Cut back on caffeine

Australian guidance is to keep caffeine under 200 milligrams a day, which is about two cups of instant coffee. Tea, cola and chocolate count too, and energy drinks aren't recommended in pregnancy. It's also safest not to drink any alcohol.

Food safety in early pregnancy

The main things to watch are listeria, a bacteria that can be harmful in pregnancy, and mercury in some fish.

Enjoy

  • Hard cheeses like cheddar and parmesan
  • Pasteurised milk and yoghurt
  • Freshly cooked meat, chicken and fish
  • Eggs cooked until firm
  • Well-washed fruit and vegetables
  • Seafood cooked and eaten hot

Avoid or limit

  • Soft cheeses like brie, camembert, ricotta and feta, unless cooked until steaming hot
  • Deli meats, pâté and pre-cooked chilled chicken
  • Raw or undercooked eggs, meat and seafood, including oysters and sushi
  • Cold cooked prawns and smoked salmon
  • Pre-packaged salads, sprouts and soft-serve ice cream
  • High-mercury fish like shark (flake), swordfish and marlin

Easy snack ideas

  • Apple slices with cheddar or peanut butter
  • Wholegrain toast with a firm-cooked egg
  • Pasteurised Greek yoghurt with fruit
  • Hummus with veggie sticks
  • Mashed avocado on crackers
  • A handful of trail mix

Avoid overheating

A high body temperature in early pregnancy has been linked to a higher risk of neural tube defects. Skip hot tubs, spas and saunas for now. Warm showers and baths are fine.

Hand over the kitty litter

Cat poo and garden soil can carry toxoplasmosis, an infection that can harm a developing baby. Ask someone else to change the litter, or wear gloves and wash your hands afterwards. Wear gloves when gardening too.

Medicines, X-rays and cleaning

Check any medicines or supplements with your GP or pharmacist, and tell your dentist or radiographer you might be pregnant before an X-ray. When cleaning, keep the room well ventilated, wear gloves and never mix products like bleach and ammonia.

Your to-do list for week 3

Helpful for this stage

Pregnancy and birth booksReading for the months aheadShop books MaternityComfort essentials for pregnancyShop maternity

Week 3 FAQs

Can I take a pregnancy test at 3 weeks?

It's usually too early. Your body only starts making hCG, the hormone pregnancy tests detect, once implantation begins. For the most reliable result, wait until the day your period is due, around the end of week 4.

What does implantation bleeding look like?

Implantation bleeding is light spotting that's usually pink or brown and lasts a day or two. It's much lighter than a period, and not everyone has it. See your GP if you have heavy bleeding or strong pain.

Can you have symptoms at 3 weeks pregnant?

Some people notice light spotting, mild cramping, bloating or tender breasts. Most don't notice anything until after they've missed a period, and that's completely normal.

What foods should I avoid in early pregnancy?

Avoid foods with a higher risk of listeria, such as soft cheeses, deli meats, pâté, pre-packaged salads and raw or cold seafood. Limit fish that are high in mercury, such as shark (flake), swordfish and marlin, and avoid alcohol.

How much coffee is safe in pregnancy?

Australian guidance is to keep caffeine under 200 milligrams a day. That's about two cups of instant coffee. Remember tea, cola and chocolate contain caffeine too, and energy drinks aren't recommended.

This article is general information and isn't a substitute for advice from your doctor or midwife.

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