The menstrual cycle can be divided into three different phases – the follicular phase, ovulation and the luteal phase. Each phase of the menstrual cycle has a different function and are regulated by several hormones, which can explain the variations in cycle length.
The follicular phase lasts from the first day of your period to the day of ovulation. During this phase, your body begins to prepare itself to accept and support a pregnancy. The endometrium (lining of the uterus) grows and thickens, and the vaginal environment also changes in order to become more sperm friendly. In the ovaries, several ovarian follicles (small sacs in which the egg matures) develop, of which one becomes dominant before ovulation. This phase is called the follicular phase because growth and maturation of the egg/ovule occurs inside a follicle, and the two hormones dominating the follicular phase are follicle-stimulating hormone (FSH) and estradiol (a form of oestrogen).
Ovulation is the key event of the menstrual cycle. Each cycle, only one egg is released from the dominant ovarian follicle in response to a surge in luteinising hormone (LH), and can only be fertilized for up to 24 hours after ovulation. It is important to accurately identify when you are ovulating if you are trying for a baby in order to maximize your chances of getting pregnant.
The luteal phase is the final phase of the menstrual cycle and lasts from your day of ovulation to the last day before your next period. Glands in the endometrium (lining of the uterus) secrete proteins in preparation for the implantation of the fertilized egg (embryo). If you get pregnant, the embryo will implant itself in the endometrium during this phase. If implantation does not occur, the endometrium starts to break down and is eventually sloughed off: this is menstruation. The luteal phase is named after the corpus luteum (Latin for “yellow body”), a structure that grows in the ovary. The luteal phase is dominated by progesterone, which is also the hormone responsible for the rise in body basal temperature (BBT).
Precise identification of your ovulation day allows you to time your baby-making intercourse for the most fertile days of your menstrual cycle to increase your chances of getting pregnant.
Confirmation of ovulation in the home environment is only possible through measuring body basal temperature (BBT). The exact determination of your day of ovulation also allows investigation of the length of your luteal phase, which will help you know when to expect your period or a positive pregnancy test result.