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Female reproduction - The menstrual cycle

The menstrual cycle - The basis for the development of life

You have most likely been very focused on your menstrual cycle, because when a couple are trying for a baby, one of the first and most important questions relates to ovulation. As with many other processes in the body, the menstrual cycle is also controlled hormonally and precisely by the midbrain (the hypothalamus). Hormone signals are sent from here to the pituitary gland (a hormone-producing gland at the base of the brain), which stimulates production of the sex hormones FSH (follicle-stimulating hormone) and LH (luteinising hormone). 

The first half of the menstrual cycle (days 1–14)

With the increased production of FSH, one–three eggs start to ripen in the ovaries. Each of these eggs is located in a follicle, which is responsible for the formation of the female sex hormones (oestrogens). These hormones build up the lining of the womb (endometrium) and open the neck of the womb (the cervix) ever so slightly. They also promote the production of cervical mucous making it easier for the sperm cells to enter the womb.

The middle of the menstrual cycle (around days 14–16)

During the middle of the menstrual cycle, the follicles are fully ripe and produce maximum amounts of oestrogen. Due to the increased levels of oestrogen, the pituitary gland excretes large amounts of LH. This sex hormone causes the follicle to burst so that the egg is released from the ovary—a process called ovulation. The remainder of the follicle forms the yellow body (corpus luteum), which produces the hormone progesterone. If fertilisation takes place, progesterone helps to preserve the pregnancy. The ripe eggs will be taken up by the fallopian tube and transported towards the womb. The eggs are viable and can be fertilised for about 24 hours. 

The second half of the menstrual cycle (around days 17–28)

The egg can be fertilised while it is in the fallopian tube. If a sperm cell reaches the egg and is successful in penetrating the shell, the egg divides several times even before it reaches the womb. Four to five days later, the fertilised egg implants in the endometrium. This immediately begins to emit the neurotransmitter hCG (human chorionic gonadotropin, the so-called pregnancy hormone) to preserve the pregnancy.

If the egg in the fallopian tube is not fertilised, this is registered by the ovary as hCG signals from the womb stop. The corpus luteum that was formed by the remainder of the follicle degenerates after days 10–14. This means that the level of progesterone in the woman’s blood falls and the endometrium is shed. Thus the first day of a new menstrual cycle begins. 

Female reproduction: When is the optimal time for fertilisation?

After ovulation, an egg can be fertilised for about 24 hours. Sperm cells can survive in the woman’s body for 48 hours or longer. Therefore, the optimal time for fertilisation starts two days before ovulation and ends one day after ovulation. As ovulation does not always occur on the same day of the menstrual cycle and cannot be determined unequivocally, days 9–16 in the menstrual cycle are considered to be the optimal time for fertilisation. 

You are welcome to contact us if you have any questions about this or other subjects: Our experts would be delighted to help you based on your individual situation. 

Female reproduction: The menstrual cycle is controlled as follows:

Hypothalamus: The hypothalamus is responsible for vegetative body functions

The pituitary gland: A gland at the base of the brain that plays a crucial role in controlling hormones 

Gonadotropin-releasing-hormone (GnRH): A releasing hormone, which sends signals from the hypothalamus to the pituitary gland and stimulates the formation of sex hormones

Follicle-stimulating hormone (FSH): Female sex hormone that is produced in the pituitary gland and stimulates the growth and development of the eggs

Luteinising hormone (LH): A female sex hormone that is produced in the pituitary gland and concludes the egg maturation process

Oestrogen: A female sex hormone that is produced in the ovary and contributes to the development of the endometrium

Progesterone: The corpus luteal hormone. Is produced by the corpus luteum and is responsible for preservation of the pregnancy in the early stages

hCG: Human chorionic gonadotropin, the pregnancy hormone

We are here for you!

Please feel free to contact us!

Our opening times:

Mon and Thu: 08:00 - 18:00
Tue, Wed and Fri: 08:00 - 16:00
Sat, Sun and holiday: 08:30 - 15:00

Schedule an appointment:

Fill out the contact form

✉ info[at]storkklinik.dk
+45 32 57 33 16

We look forward to hearing from you!