Cervix or cervix uteri is the lower part of the uterus that can be felt in the vagina. The cyclic changes of the cervix, like the cervical mucus, are another sign to observe the menstrual cycle.

The calendar method is one of the first natural family planning methods. Here the ovulation is calculated based on the cycle length.

Luteinizing hormone. It is controlled by the pituitary gland and is responsible for the formation of the corpus luteum.

Menstruation, also known as bleeding or a period: Every cycle, a layer of mucous membrane is built up in the uterus, a nest for the fertilized egg cell. If pregnancy does not occur, this layer of mucous membrane is expelled with menstruation.

NFP stands for natural family planning and is the generic term for all methods of natural family planning.

The Pearl Index assesses the safety of contraceptives. The smaller the Pearl Index, the safer the contraceptive.

PMS stands for premenstrual syndrome. It refers to the emotional and physical discomfort associated with the menstrual cycle.

The vagina is a muscular tube that connects the uterus to the vulva.

Testosterone is a sex hormone found in both men and women, but in different concentrations.

Cervical mucus is produced in the glands of the cervix. It is influenced by the hormones estrogen and progesterone and changes its appearance and consistency during the menstrual cycle.

The cycle begins on the first day of menstruation and ends on the last day before the next bleeding.

Conception or fertilization is the moment when the egg and sperm fuse and a new human being is created.

Corpus Luteum or yellow body is formed in the ovary after ovulation. The hormone progesterone is formed in the corpus luteum.

Implantation or nidation refers to the implantation of the fertilized egg in the lining of the uterus.

The egg cell or oocyte is the female germ cell, the carrier of the female genetic material.

The follicle or egg membrane is the covering of the maturing egg.

The fertility window or fertile period is the period in the cycle when you can get pregnant. This period begins four days before ovulation and ends two days after ovulation.

The uterus or womb is one of the female reproductive organs. The fertilised egg nests in the uterus after conception and grows here until birth.

Corpus Luteum or yellow body is formed in the ovary after ovulation. The hormone progesterone is formed in the corpus luteum.

Core body temperature is the temperature measured in the body. Core body temperature rises due to the influence of the hormone progesterone after ovulation.

The luteal phase is a phase of the menstrual cycle. It begins the day after ovulation and ends on the last day of the cycle.

Mittelschmerz is a short cramping pain in the left or right lower abdomen triggered by ovulation. It is one of the secondary signs of fertility and can only provide additional clues about the fertile period.

Estrogen is a sex hormone. It is produced in the maturing egg cell. Among other things, estrogen causes the cervical mucus to change. The more estrogen is produced, the clearer and more spinnable the cervical mucus becomes.

Menstruation, bleeding or also called period: Every cycle, a layer of mucous membrane is built up in the uterus, a nest for the fertilized egg. If pregnancy does not occur, this layer of mucous membrane is expelled with menstruation.

Progesterone is a sex hormone. It is produced by the corpus luteum. Among other things, progesterone causes the body's core temperature to rise.

Temperature method is a method of natural family planning. The hormone progesterone causes the temperature to rise after ovulation. This temperature rise is observed and used to determine ovulation.

Contraception refers to the prevention of conception. There are three main types of contraception: hormonal, mechanical or natural.

Vaginal bleeding is bleeding associated with ovulation. It is a secondary sign of fertility and can only provide additional clues about the fertile period.