• Nutrition

3rd Week of Pregnancy

embryo developing

A Little Zygote Forms

Baby's Growth and Development at 3 Weeks: Fertilisation and Implantation

Although you don't know it yet, you might have conceived already! Fertilisation occurs when an egg and sperm connect and form a single cell, called a zygote.

Here’s what’s going on during your 3rd week of pregnancy:

  • By the 3rd week of pregnancy, the microscopic-sized zygote divides again and again, growing at an astounding pace in your baby.
  • At 3 weeks pregnant, your baby already has all of the genetic material she needs for life — half of the 23 pairs of chromosomes from you and half from your partner.
  • Your baby's sex already is determined.

The Great Divide

Approximately 12 hours after fertilisation, your baby — right now only a one-celled zygote — divides into two identical cells. These two cells each split, creating four cells, which then split to become eight. This continues as the total number of cells in your baby doubles every 12 hours.

If a single zygote splits into two identical zygotes, each with the same genetic makeup, identical twins occur.

During your 3rd week of pregnancy, your zygote is moving down the fallopian tube to your uterus.

Your Changing Body at 3 Weeks Pregnant: Fertilisation and Implantation

A pregnancy test kit

You’re 3 weeks pregnant now, but it's too early for you to have missed your period or to experience any symptoms.

Here’s what’s happening inside during your 3rd week of pregnancy:

  • At 3 weeks pregnant, your baby is in the blastocyst stage. Your developing placenta begins producing hCG (human chorionic gonadotropin), the hormone that’s detected in your blood or urine to tell you that you’re pregnant.
  • A home pregnancy test can detect this hormone about six to 12 days after fertilisation.
  • Only two weeks after your cycle, your uterus is thick with a rich blood supply — ready to accept and nourish your fertilised egg.
  • In the 3rd week of pregnancy, your baby implants in the lining of your uterus and you might notice spotting. You even could mistake this for the start of your period. This spotting might be the first real sign that you're pregnant! It usually only lasts one to two days and is lighter than your normal period.

Wellness and Nutrition at 3 Weeks Pregnant: Fertilisation and Implantation

A lady doing stretches on an exercise mat


If you’re already in good condition and regularly exercising, pregnancy doesn’t prohibit you from continuing with a safe exercise routine.

At 3 weeks pregnant, just remember:

  • Drink plenty of fluids.
  • Respond right away if your body indicates that you should slow down or even stop.
  • Avoid smoking, alcohol, medication, or exposure to chemicals.

Nutrition for Two

Even earlier than the 3rd week of pregnancy, how well you eat and care for yourself makes a big difference in the quality of nutrition your unborn baby receives.

What Do the Nutrients in Your Food Do?

  • Calories help nourish your growing baby.
  • Iron and folic acid help make the extra blood needed during pregnancy.
  • Protein helps produce blood and builds your unborn baby's tissues and muscles.
  • Calcium builds your unborn baby's bones and teeth.

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