The egg has been fertilized, moved into the uterine cavity and the germ of the baby is not older than seven days. It was described in the 3rd part of “pregnancy week by week” series . What happens inside your belly in the week 4 will be describe now.
4 weeks pregnant
You should start regular menstruation this week. However, nothing happens so far or the bleeding is just weak. You are entering the second lunar month of pregnancy.
Although fertilization may not always turn out well because a number of the pregnancies ceases in this critical period due to the developmental disorder or wrong implantation of the egg in the womb. A dead egg leaves the body with menstruation.
Most women are still unaware of their pregnancy at this point. Some begin to be annoyed with various odours, nausea can appear, need to urinate is much frequent.
What happens in the week 4?
The embryo has implanted into the uterine lining which completely surrounds it now. It grows bigger every day. The ovaries produce progesterone which enriches the lining of the womb so it was strong enough.
At the beginning of the 4th week of pregnancy there are created two cellular layers called endoderm, the internal embryonic layer and ectoderm, the external embryonic layer. Cells multiply rapidly and some reach the arteries of the uterine lining. After the penetration of the arteries the maternal blood flows into the cavities of the cover.
Maternal blood provides nutrition of the fetus and supply of oxygen from this moment throughout the entire pregnancy.
If the fetus is successfully implanted, it produces hCG hormone (human chorionic gonadotropin). At this moment, a doctor can confirm pregnancy based on the blood test or ultrasound exam.
For your first assurance that you are pregnant, just use a pregnancy test from the drug store, which proves the presence of the of hCG in the urine. It is highly sensitive.
The embryo is entirely burrowed in the womb. The fetus is tiny, measuring just 0.1 – 0.2 mm and is getting surrounded by an amniotic cavity. Oxygenated blood travels through the uterine artery, deoxynated blood leaves through veins. At the end of this week, the fetus is surrounded by a thin mucous membrane, which completely separates it from the uterine cavity.