Fertility is the reproductive ability of a woman, meaning her ability to conceive and get through a pregnancy successfully. There appear to be many factors that affect fertility, but age is the most important independent factor.
Oocytes
In comparison to men, who can produce sperm throughout their life, a woman is born with the whole of her genetic material that is reduced year by year.
Women are born with more than 3.000.000 immature oocytes. During adolescence, the number of oocytes is reduced in 400.000 and out of these only 400 are going to mature and become capable of fertilisation.
Usually, a fertile woman produces a mature oocyte (egg) during each menstrual cycle. As a result, 400 mature oocytes correspond to 400 normal cycles that a woman is expected to have during her lifetime.
Ovulation
Ovulation is the process of the release of an oocyte that can be fertilised.
For the maturation of the ovarian follicle and the release of an oocyte, two weeks are usually required. In the first stage of the menstrual cycle, the hypophysis excretes the hormone FSH that later on triggers the ovary for the production and the maturity of one or more follicles. The follicles during their development produce oestrogens. The increase of oestrogens causes a negative control in the FSH production and as a result its production is decreased. That decrease in FSH permits in only one of the ovarian follicles to continue its growth until the final stages. The continuous increase of oestrogens leads to the production of the LH hormone from the hypophysis. In a menstrual cycle of 28 days, the sudden increase of LH on the 12th day of the cycle helps the follicle to mature and to release the mature oocyte (ovulation).
Ovulation occurs 36 hours after the increase of LH. Right after its release, the oocyte is transferred into the fallopian tubes where it can be fertilised.
After the ovulation, the empty follicle is transformed into a cyst “the corpus luteum cyst”. That cyst is important as it produces hormones like progesterone, which in cooperation with the oestrogens matures the endometrium i.e. the lining of the uterus, for the implantation of the embryo.
If the egg is not fertilised, progesterone decreases gradually and 14 days later the menstrual cycle starts.
When are you most fertile?
The fertile window is the period within a month when you have higher chances of conceiving.
Ovulation is usually conducted 14 days before the menses, so in a woman with a cycle of 26 days, we estimate that she is ovulating on the day 12 of her cycle. In a cycle of 28 days, ovulation is conducted on the 14th day.
Evidence shows that a woman has the strongest possibility to conceive if she has unprotected sex within a time range of 4 days before and 2 days after her ovulation.
For a woman with a cycle of 28 days, who ovulates the 14th day, the best time to try to conceive is from the 10th day till the 16th day of her menstrual cycle.
How often do you need to have sexual intercourse?
Ideally, day after day since the sperm survives into the fallopian tube for two days or more.