Human reproduction is a result of the union of the sperm with the egg, their union will result in the embryo that will develop in the uterus in order for a child to be born.

During the menstrual cycle, ovulation occurs at about day 14 of a 28-day menstrual cycle. Specifically, ovulation is the release of the egg from a woman’s ovary. The egg begins its five-day trip through the fallopian tube to the uterus. As the egg travels through the fallopian tube, the level of progesterone hormone, rises, which helps prepare the uterine lining for pregnancy.

The egg lives 24 hours only. If there is sexual intercourse on fertile days, the semen is deposited in the vagina and lives about 3 days. Conception occurs when a spermatozoon from a fertile man swims up through the vagina and uterus and meet the egg in the fallopian tubes. So, although the fertile day in the strict sense of the term, is only one, owing to the long life of the sperm and the relative instability of ovulation, days 6-7 days around ovulation, are the ones considered as fertile (-dangerous-).

In the fallopian tube the egg will be fertilized by a single sperm. As the fertilized egg continues to move down the fallopian tube, it begins to divide into two cells, then four cells, then more cells as the division continues. About a week after the sperm has fertilized the egg, the fertilized egg travels to the uterus and becomes a growing cluster of about 100 cells called a blastocyst. Then, on the 5th day, the blastocyst migrates to the uterine cavity, attaches itself to the lining of the uterus (the endometrium) implants into the endometrium and continues its growth.

Eleni Katsiani
Biologist MSc, PhD