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Pregnancy Week 4

Fetal Development at week 4

Congratulations! You (well, your body) have finally officially met your developing baby. The two of you are now intimately joined, and your body begins to mobilize to support your baby’s growth. You don’t realize it yet, but you’ve been pregnant for a whole week!

Your Baby

By now the embryo has actually sunk beneath the surface of your uterus. The amniotic sac (the water-tight bag of waters) and the amniotic cavity (the area within the womb that contains the amniotic sac, amniotic fluid, and developing child) have begun to form. The yolk sac, which eventually gives rise to the baby’s digestive tract, and a primitive version of the umbilical cord called the umbilical stalk appear. The amniotic sac, amniotic cavity, and yolk sac form over the next six days to create an environment in which your baby can grow and develop.

Your embryonic baby grows rapidly. The amniotic sac, amniotic cavity, primitive umbilical cord, and yolk sac continue to develop.

The divided cell mass now looks like two hollow balls opposing each other suspended from a thick, short umbilical stalk and encased by a fluid-filled bubble. Your embryonic baby measures only 0.2–0.3mm in length, or about the size of a poppy seed.


The hormone level within your body rises dramatically during pregnancy. 50-90% of women experience nausea as their bodies adjust to the increase in pregnancy-supporting hormones (estrogen, progesterone, and hCG) and changes in carbohydrate metabolism. Much of the time, nausea is provoked by sharp odors, especially cooking smells. Open a window or turn on a fan to help circulate the air.

It is from this point forward that a pregnancy testing kit will definitely register a positive or negative result, so if you’re still reading up about early pregnancy symptoms then a trip to the pharmacy will soon give you a definitive answer!

Things to do when four weeks pregnant

  • Take a pregnancy test if you’ve missed your period.
  • Tell your partner the news, if you haven’t done so already!
  • Consider whether taking pregnancy supplements would be beneficial for you – Folic acid should be a minimum.
  • If you’re working, quietly check what your employer’s maternity leave policy is so that you’re prepared when you reveal the big news.
  • Contact your doctor – some will ask you to come in for a blood test with a nurse to confirm your pregnancy, before scheduling you for your first ultrasound scan at around 12 weeks.