Conception is a series of processes that follow after fertilization, as a result of which a new organism is born and continues to develop in the female body, that is, pregnancy occurs. Several factors precede the onset of pregnancy:
• Sexual intercourse between a man and a woman (without protective equipment).
• Fertilization.
After sexual contact, male sex cells (sperm) penetrate into the uterine cavity, from where they continue their way to the fallopian tubes. Fertilization occurs directly in the fallopian tube (one or both at once), where the sperm must meet the egg. For a successful meeting of the female germ cell and sperm, full ovulation is necessary. During ovulation, the main follicle ruptures in the ovary, from which a physiologically normal egg is released, ready for fertilization. Her path also lies in the direction of the fallopian tube. When several hundred million spermatozoa collide with an egg in the cavity of the tube, only one merges with it. A fertilized egg is called a zygote, which continues to move towards the uterus, at the same time splitting up, as a result of which more and more new cells of the future embryo appear.
This process is not yet a pregnancy, since a fertilized egg may die before reaching the uterine cavity, or, on the contrary, once it enters the uterus and fails to implant for any reason, it is expelled from the fetus along with menstrual flow. A similar phenomenon is called spontaneous interruption of biochemical pregnancy.
• Implantation.
As soon as a fertilized egg (now a blastocyst) enters the uterus, it begins to intensively penetrate into the thickness of the endometrium - to be implanted. At the same time, the uterine mucosa, under the influence of progesterone, continues to thicken and envelops the blastocyst around the entire circumference. A chemical and physical relationship is formed between the future embryo and the endometrium, the blastocyst trophoblast begins to synthesize chorionic gonadotropin, which causes the ovarian corpus luteum to continue to secrete progesterone, which is necessary for further prolongation of pregnancy. As a result, menstruation does not occur, and we can talk about the onset of pregnancy.
The time interval from the moment of sexual contact to implantation takes 7-12 days, so it is premature to talk about the first signs of pregnancy in the early stages of 1 week after intercourse.