The female reproductive cycle

When couples want to conceive, the first and most fundamental question is usually about what days the woman (or person with female organs) is fertile.

Like so many bodily processes, the menstrual cycle ⁠— also known as the female reproductive cycle ⁠— is controlled by hormones, predominantly follicle-stimulating hormones (FSH) and luteinising hormones (LH).

The basis of human conception

First half of the cycle (days 1 to 14)

When FSH is increased, one to three eggs (ova) start maturing.

Each of these eggs is located in a follicle in the ovary. These follicules are responsible for producing the main female sex hormone, oestrogen. This hormone causes the uterine lining (endometrium) to form and the neck of the womb (the cervix) to open slightly.

It also promotes the production of thin, watery discharge (cervical secretion). This, and all of the other physiological occurances during this stage, take place to better facilitate penetration of the sperm into the uterine cavity.

Middle of the cycle (approx. days 14 to 16)

The follicles are fully matured and are producing the maximum amount of oestrogen. This kick-starts the pituitary gland to increase secretion of LH, which ensures that the follicle breaks apart, allowing the egg to be released from the ovary ⁠— this is ovulation.

Progesterone, a hormone, is produced by so-called yellow bodies, which are formed by the follicle's remains. The egg is caught by the fallopian tubes which direct it towards the uterus, which should be full wiht endometrium and ready to support any fertilised egg. The fertilisation must take place within 24 hours.

Second half of the cycle (approx. days 17 to 28)

The egg can be fertilised while it is in the fallopian tube or in the uterus. If sperm reaches the egg while it is still in the fallopian tube and succeeds in penetrating it, the egg will divide several times before it has even reached the uterus.

After another four to five days, the embryo should implant in the uterus, which will immediately start releasing human chorionic gonadotrophin (hCG), also called 'the pregnancy hormone'.

If this hormone is not released, then the ovary recognises that fertilisation has not taken place.

The yellow bodies perish in 10-14 days, which causes a drop in progesterone that results in the endometrium to disolve and bleed out of the uterus. This is what causes a woman's period, and marks the first day of the new cycle.

What is the best time for fertilisation?

The egg is capable of being fertilised for around 24 hours once ovulation has occurred. Sperm can actually survive for 48 hours, sometimes more, in a woman's body, during which time, fertilisation can occur.

The optimum window for fertilisation is therefore two days before ovulation and a day after. But, since ovulation does not always take place on the same day of the cycle and if often hard to predict, it's generally considered that (for women with regular cycles) the 9th to the 16th days of the cycle are the best for trying to conceive.

If you have any questions about this or other issues, please contact us at any time.

How the female cycle is controlled

The hypothalamus: the midbrain or interbrain, responsible for the vegetative bodily functions
The pituitary gland: the hypophysis, plays a decisive role in the control of the hormonal system
Gonadotrophin-releasing hormone (GnRH): sends signals from the hypothalamus to the pituitary gland and stimulates the production of sex hormones
Follicle-stimulating hormone (FSH): a female sex hormone that is produced in the pituitary gland, it stimulates the growth and development of the eggs
Luteinising hormone (LH): a female sex hormone that is produced in the pituitary gland, it ends the maturing process of the egg
Oetrogesn: a female sex hormone that is formed in the ovary, it causes the formation of the endometrium
Progesterone: yellow body hormone that is formed in the yellow body and is responsible for sustaining the pregnancy in the early stages
hCG: human chorionic gonadotropin, the so-called pregnancy hormone

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