The process of natural conception

Human reproduction is a result of the union of a sperm with an egg. Eggs are produced in the ovaries and sperm in the testes.

The union of the sperm with the egg, will result in the embryo that will grow in the uterus so that the child is born.

If there is intercourse during the "fertile days", the sperm will concentrate in the vagina wall. The sperm will pass through the external cervical os, which is the gateway between the vagina and the internal sex organs and is open during the "fertile days". The sperm will then go through the cervical canal towards the uterine cavity and through the proximal tubal ostium to reach the fallopian tubes.

The fallopian tube will then receive the egg that was recently released with ovulation, via its fimbria. Sperm and egg meet in the ampulla of the fallopian tube and this is where the egg will be fertilised by only one sperm. The fertilised egg (zygote) will remain in the fallopian tube for 5-6 days, where it divides into 2, 4, 8 cells and then becomes a morula and a blastocyst.

As a blastocyst (an embryo with around 6-120 cells) it will then migrate towards the uterine cavity and implant by invading the endometrium where it continues to develop.

Requirements for conception


  • The tubes to be open and functional in order to receive the egg from the corresponding ovary and allow the sperm to reach the egg.
  • Sperm with normal parameters, meaning that the spermatozoa should be in satisfactory numbers and have a good progressive motility so that some of them will manage to bypass any obstacles and reach the egg.
  • Ovulation to take place, so that the mature egg is released from the Graafian follicle.
  • Intercourse during the fertile days.


It is also known that:

  • Endometriosis can greatly reduce fertility.
  • In around 25-30% of all subfertility cases the cause is unexplained.