Cycle biology

  • How long is a normal cycle?
  • How broad is the variation?
  • Why is my cycle different?
  • When is my fertile period?

Questions in the field of cycle knowledge become relevant as soon as girls reach puberty or women (have to) deal with family planning.

Thus, until 90 years ago, the female cycle and its connection to conception and pregnancy gave people quite a lot of puzzles. And, by the way, still does so today. Even in the Western world, not every woman or man knows what parameters determine women getting pregnant at a very specific time. Doctors Knaus & Ogino laid the foundation for this. It is precisely these findings that cycleduc® is based on. 

Female cycle

During the fertile years, the female body prepares for the fertilization of an egg and its implantation in the uterus in a monthly recurring rhythm.

A finely regulated interaction of hormones causes their concentrations in the blood to increase and decrease in a monthly rhythm, similar to a wave movement.
The hormones stimulate the growth of a follicle, which forms more and more estrogen with increasing growth. After ovulation, the follicle becomes the corpus luteum, which forms the corpus luteum hormone. Due to the estrogen, the mucous membrane of the uterine cavity has grown, the progesterone now causes a further preparation of the uterine mucosa for the implantation of the fertilized egg.

The main hormonal changes in the female cycle take place in the ovary in three phases:

Follicle phase: The follicle-stimulating hormone (FSH) stimulates the growth of 20 to 25 follicles in the ovaries. They produce estrogens (estradiol), which they release into the blood. One follicle in one of the two ovaries becomes particularly large (average up to 20 mm) and reaches full maturity, the others die and are absorbed.

Ovulation: The large amounts of estrogen stimulate the pituitary gland to release the luteinizing hormone LH. The high LH level causes the surviving follicle to release the mature egg into the oviduct. Ovulation takes place. The egg can now be fertilized for about 24 hours.

Luteal phase: The follicle converts into the corpus luteum, which produces the hormones progesterone (yellow body hormone) and – in small amounts – estrogen. Progesterone and estrogen together inhibit the release of FSH and LH by the pituitary gland. If there is no pregnancy, the corpus luteum perishes after 10 to 12 days, causing the concentrations of progesterone and estrogen in the blood to drop sharply. This triggers menstrual bleeding. Due to the sharp decline of the ovarian hormones estrogen and progesterone, the release of FSH and LH is no longer suppressed – a new cycle begins.