Menstrual cycle
The menstrual cycle begins on the day on which the bleeding begins properly. Small spotting is not yet considered the beginning of a new cycle.
How is the menstrual cycle determined?
The menstrual cycle begins on the day on which the bleeding begins properly. Small spotting is not yet considered the beginning of a new cycle. If the bleeding starts at night or in the evening after 6 pm, the first day of the menstrual cycle is the next day.
The menstrual cycle continues until the start of the next bleeding. Therefore, each cycle includes one menstruation. The average cycle length is 28 days, but there is a lot of variation between individuals. Cycles of 23–35 days are still considered normal.
Learn more about studying the menstrual cycle
Getting pregnant during ovulation
The onset of pregnancy is possible when the egg is released at the time of ovulation. The exact time of ovulation depends on the length of the menstrual cycle. Ovulation always occurs 12–14 days before the start of the next bleeding. Therefore, ovulation in a regular menstrual cycle of 26–29 days is approximately on the 12th–15th day of the cycle. If the cycle is very short or long, ovulation can occur around the 10th day or the 18th day of the cycle. The egg is fertile for only about 24 hours after ovulation. High-quality sperm can remain fertile for two to three days in the fallopian tube.
Previously, the exact time of ovulation has been determined by measuring the basic temperature. However, this is not useful as the temperature only rises after ovulation when the fertile period is already over. An ovulation test is the only option for determining the time of ovulation. Digital tests are the easiest to interpret.
Menstrual cycle
The menstrual cycle is regulated by pituitary hormones. At the beginning of the cycle, FSH secreted by the pituitary gland causes the ovarian follicle to mature. The oestrogen produced by the ovarian follicle thickens the endometrium.
The mature follicle bursts and the egg is released. This is called ovulation. It begins as a result of the rapid release of high levels of luteinising hormone (LH) from the pituitary gland.
A corpus luteum develops in the place of the follicle. The luteinising hormone supports the function of the corpus luteum and the secretion of progesterone, which in turn matures the endometrium for pregnancy.
However, if the egg is not fertilised and implanted, the corpus luteum atrophies and the menstrual cycle begins again. Thus, the endometrium is renewed every month in order to stay in the best possible condition.
