By pregnancy week 4, your baby would have grown into a large ball of about a hundred cells. At this stage, this large ball of cells is known as a blastocyst. By the later half of pregnancy week 4 (about 12 days post fertilization), the blastocyst would have successfully implanted itself into your womb!

Before your body recognises the pregnancy, the blastocyst has to complete a series of steps.

  1. The blastocyst has to hatch from the outer covering of the original egg.
  2. After hatching, the blastocyst floats around the uterus for several days, searching for a suitable and welcoming location to burrow itself into the uterus. Usually, the chosen location is at the roof of the uterus (womb).
  3. Once implanted, the blastocyst gradually differentiates into 2 parts.
    • The first group of cells will eventually form the placenta while
    • The other part becomes the developing embryo.

Also, the blastocyst secretes a hormone called Human Chorionic Gonadotrophin (HCG) which tweaks your immune system and prevents your body from seeing it as a foreigner. Therefore, the blastocyst is preventing itself from being attacked.

The above processes are so important, and any failure of them successfully occurring may result in a miscarriage.

In a normal pregnancy, HCG levels double every second day (36-48 hours). Initially, HCG levels might be too low to detect in your urine with an over-the-counter pregnancy test kit. Therefore, you might have to wait roughly a week after intercourse to obtain a positive result.

The rising HCG levels are responsible for some of the symptoms that you may experience later in pregnancy.

On a side note, signals in the form of the hormone progesterone are being transmitted to your brain to tell it you are pregnant and to temporarily stop those monthly periods. This prevents your uterine lining from being shed.

Ref: N18