Pregnancy week 3 - baby's development and your body

Week 3 is the first week after fertilization. Immediately after fertilization, the cells begin to divide and increase in number, and the fertilized egg now moves down from the fallopian tube to the uterus. After about 3-4 days, it reaches the uterus, and after about 6-8 days, it will have embedded itself in the uterine lining.

Size:

The embryo is about 0.1–0.2 cm or 0.039–0.079 inches in size, from head to rump.

Weight:

Too small to estimate.

Embryo development:

At fertilization, the sperm and egg form a single-celled unit called a zygote. The zygote normally has 46 chromosomes — 23 from the biological mother and 23 from the biological father.

The zygote moves down the fallopian tube toward the uterus. The cell divides rapidly and soon starts to resemble a mulberry, called a morula.

Toward the end of this week (or the beginning of the next), the rapidly growing little ball of cells may attach itself to the uterus. It does this by embedding into the uterine lining.

Your body:

Since fertilization has just occurred, it’s unusual to experience pregnancy symptoms during this early stage. However, some may notice subtle changes in the symptoms they typically feel after ovulation.

Toward the end of this week (or the beginning of the next), some may sense implantation occurring. This can feel like a brief, sharp pain at a specific point in the uterus or a mild, dull ache.

With implantation, a small amount of bleeding may also occur, known as implantation bleeding.