From bottom to top, the open- accessible fertilisation “path” is defined by
- Clean and balanced vaginal environment
- Anatomic cervix with satisfactory production of sperm-friendly mucus
- Anatomic and sterile intrauterine cavity and
- Permeable fallopian tubes
After ejaculation, the man’s sperm is deposited in the posterior vaginal dome. The sperm at this moment has a gelatinous form but quickly liquefies. It is obvious that once liquefied a large part of it will come out of the vagina. This is a completely normal procedure and therefore it is pointless to sit in bed hours after intercourse or to be disappointed if sperm excess is noticed after intercourse.
The first obstacle that the sperm encounters on its journey to the fallopian tubes is the cervical mucus which is largely affected by the woman’s hormonal condition but also by the presence or absence of germs in the vagina. The cervical mucus before ovulation is rich in quantity, watery, thin and easily permeable by sperm while a few hours later it becomes thick and practically impermeable.
This increased production of mucus can allow sperm to penetrate several days (up to 3) before ovulation. Provided that the interested couple comes into frequent contact (at least 2-3 per week) there is a minimal chance that they will not succeed the ovulation window.
Having overcome this obstruction of the cervical mucus, the sperm must pass through the endometrial cavity and reach the fallopian tubes. Although practically sperm only needs a few minutes to reach the fallopian tubes from the vagina, our body structure is such that eventually allows waves of sperm continuously to reach the fallopian tubes even many hours after intercourse. This seems to be nature’s prediction to avoid synchronization mismatch between intercourse and ovulation, and therefore, it is estimated that at least 15% of the sperm released will reach the fallopian tubes.
As long as the fallopian tubes are permeable, they allow the sperm to meet the egg and fertilization to follow. Accordingly if the path for the embryo is open towards the uterus, it will be able to move to the endometrial cavity and give the much wanted implantation. On the other hand, if the tubes are blocked the embryo gets trapped and leads to ectopic extra uterine pregnancy.
