Even if we talk about the first embryonic week of pregnancy, the formation of the embryo has not yet begun. At this time, the egg meets the sperm in the ampulla of the fallopian tubes and their fusion. The cell begins to actively divide and becomes like a blackberry. Its size is no more than the tip of a ballpoint pen. In the early days, it begins to move through the fallopian tubes to the uterus, where it should gain a foothold. This promotion takes approximately 5 days. After fixing in the uterus, the umbilical cord and placenta begin to develop. The organs of the fetus are subsequently formed from the internal cells. The uterus itself becomes soft. Her neck thickens, and a mucous plug forms in it, which is designed to protect the fetus from infections.
On ultrasound, it will not be possible to detect the embryo in the first week. The doctor will only be able to determine the dominant follicle and the thickness of its walls. Some sensitive tests can detect pregnancy as early as 7-10 days after conception. But, as a rule, a woman is unaware of pregnancy until the delay of menstruation.