Here we shall see how the natural pregnancy takes place. For natural pregnancy to occur- four factors are needed. These factors are Egg / Oocyte, Sperm, Uterus and Fallopian tube. Once all these factors work in synchrony, natural pregnancy takes place.
When the bleeding of menses / periods starts it is considered as the first day of the menstrual cycle. From this day the menstrual cycle, the creation of eggs takes place; this is also called follicular-genesis. In a normal cycle around, 13th to 15th day, the size of the follicle grows up to the size of a lemon: about 18-20mm. Then it ruptures- called OVULATION. And the egg / oocyte is released. The human oocyte is very small. In common terms it is as small as one fourth the size of a dot that one can make with a pen. Hence eggs can’t be seen on sonography or with the naked eye. This egg comes in the fallopian tube.
While the egg is developing under the hormonal stimulus. Uterine lining / Endometrium grows. It creates a healthy environment for embryo implantation and growth. The thickness of this endometrium should be at least 7mm. endometrium of 10mm or more has best chance of pregnancy.
During the sexual intercourse the sperms get released at the opening of the uterus the Cervix. Important fact here is that almost 50% to 60% semen comes out of the vagina after intercourse. This happens with everybody. Weary of this some women try to do some futile exercises like remaining in a lying position, crossing legs, taking a pillow under the waist and so on….. which is not necessary.
Sperms go to the fallopian tube through the uterus. Here the fertilization takes place. For fertilization to occur. There are two obstacles for the sperms. First is the 2-3 layers of cells called cumulus and the second layer is called ZONA. Sperm has to go through these two layers to enter the egg. The cumulus cells are bound together by hyaluronic acid. Head of the sperm (Acrosome) contains the Chemicals (Hyaluronidase), which dissolve this hyaluronic acid and separate these cells away. Number of sperms required are a lot many as one sperm head has a very small amount of this chemical. Hence good sperm count is a very important factor. After separating these cells there is a layer of zona. Sperm has to penetrate this layer and get inside the egg. This required strength or force for penetration of zona, which comes from the speed of sperm. Therefore, it is necessary to check the motility of the sperms. This explains how count and motility are two important factors for the sperm.
Now the embryo is formed in the fallopian tube it is round in shape like a ball. Embryo does not have its own transport system. Therefore, the embryo is dependent on the fallopian tube for being transported to the uterus. Fallopian tubes have this responsibility to carry the embryo to the uterus. Fallopian tubes have tiny hair like stucture, which transport the embryo. Hence it is important to have functioning tubes and not just open. This is how normal pregnancy happens.