- 22nd to 28th day of embryonic development
- Length of embryo: 4 to 6 mm
Four weeks after fertilization, the changes caused by pregnancy can be clearly felt and seen. Through the influence of pregnancy hormones, the cervix and uterus are loosened, the mucous membrane of the cervix and vagina attains a bluish tint, and the uterus enlarges. Blood circulation in this area increases.
You can probably now feel the first unpleasant side effects of pregnancy: nausea, fatigue, loss of appetite, constipation, frequent urinary urges, sleeping problems and more. Look at it from a positive perspective: these are all signs of normal hormonal changes in your body and thus of a healthy pregnancy. On the other hand, if you have no symptoms at all, this is also not a problem; you may just belong to that group of women who have no trouble with this stage of pregnancy.
At the beginning of the 6th week, the embryo has a clearly elongated form. Buds grow, from which the arms and legs develop. The heart is a clear protrusion and has primitive vestibules and chambers with a partition, and the very basic blood circulation connects to the chorion (the outer layer of the placenta). In the umbilical cord, which leads to the placenta, the blood vessels connect with the mother. Now the blood vessels contain blood cells, not just liquid. The digestive tract consists of a front, centre and rear part. The lungs, liver, pancreas and thyroid gland also develop.
Tiny invaginations on the head mark the places where the ears are developing, and the inner ear has already developed. On the face, eyes are developing, and the hint of the mouth opening is already visible. Additionally, the lower jaw and vocal chord begin to take shape.
Your baby has more than doubled in size this week and is now the size of a blueberry!