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Fertility guides

The female fertility cycle

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You have probably already become intimately familiar with the details of your cycle. When couples want to conceive, the first and most fundamental question is usually about fertile days.

Like many other processes in our body, the menstrual cycle is controlled by hormones – more precisely, by the hypothalamus. From here, hormonal signals are sent to the pituitary gland, which triggers the production of follicle-stimulating hormones (FSH) and luteinising hormones (LH).

The basis for the development of new life

First half of the cycle (days 1 to 14)

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

Each of these eggs is located in a follicle, which is responsible for production of the female sex hormone (oestrogen). This hormone causes the uterine lining (endometrium) to be formed and the neck of the womb (the cervix) to open slightly.

It also promotes the production of cervical secretion, which facilitates penetration of the sperm into the uterine cavity.

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

Mid-cycle, the follicles are fully matured and produce maximum amounts of oestrogen. This increase in oestrogen causes an increased secretion of LH by the pituitary gland. The sex hormone ensures that the follicle breaks and the egg is released from the ovary – this is ovulation.

Yellow bodies, which produce the hormone progesterone, are formed from the remains of the follicle. In the event of fertilisation, progesterone helps to sustain pregnancy. The mature eggs are caught by the fallopian tubes and transported in the direction of the uterus. They are capable of surviving and being fertilised for 24 hours. 

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

The egg can be fertilised while it is in the fallopian tube. If a sperm reaches the egg and succeeds in penetrating the embryonic membrane, the egg divides several times before it has even reached the uterus.

After another four to five days, the embryo is implanted in the lining of the uterus. The uterus immediately starts sending out human chorionic gonadotrophin (hCG), also called the pregnancy hormone, to sustain the pregnancy.

If the egg is not fertilised in the fallopian tube, the ovary recognizes this, since the hCG signals were not sent out from the uterus. The yellow body perishes in 10-14 days, causing the progesterone levels in the woman’s blood to drop and the lining of the uterus to bleed out. This signals the start of the first day of the new cycle.

What is the best time for fertilisation?


The egg is capable of being fertilised for approximately 24 hours after ovulation. Male sperm can survive for 48 hours or more in the woman’s body. The optimum window for fertilisation, therefore, starts two days before ovulation and ends a day after ovulation. Since ovulation does not always take place on the same day of the cycle and cannot be clearly determined, the 9th to 16th days are the ideal time for conception.


If you have any questions about this or other issues, please contact us at any time – our experts will gladly help you.

How the female cycle is controlled


  • The hypothalamus: a.k.a. the midbrain or interbrain, responsible for the vegetative bodily functions

  • The pituitary gland: a.k.a. 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 sex hormone that is produced in the pituitary gland. It stimulates the growth and development of the eggs.

  • Human chorionic gonadotropin (hCG): a.k.a. the pregnancy hormone

  • Luteinising hormone (LH): a female sex hormone that is produced in the pituitary gland. It ends the maturing process of the egg.

  • Oestrogen: a female sex hormone that is formed in the ovary. It causes the formation of endometrium.

  • Progesterone: yellow body hormone that is responsible for sustaining the pregnancy in the early stages

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