Ovulation is a key part of the menstrual cycle in which a mature egg is released from the ovary, making it available for fertilisation by sperm.
Ovulation is a critical component of the reproductive cycle and is essential for natural conception. Understanding this process can help in planning or preventing pregnancy and in recognising potential reproductive health issues.
It typically occurs midway through the menstrual cycle and is essential for reproduction.
The ovulation process
Follicular phase
- Initiation – the menstrual cycle begins with the follicular phase, which starts on the first day of menstruation and lasts until ovulation. During this phase, the pituitary gland releases follicle-stimulating hormone (FSH)
- Follicle development – FSH stimulates the growth of several ovarian follicles (fluid-filled sacs in the ovaries that contain eggs). Each follicle produces estrogen, which helps prepare the uterine lining for a potential pregnancy
Hormonal changes
- Rising estrogen levels – as the follicles mature, they secrete increasing amounts of estrogen. This rising estrogen level signals the pituitary gland to release luteinising hormone (LH)
- LH surge – the surge in LH, known as the LH surge, triggers the final maturation of the dominant follicle and initiates ovulation
Ovulation
- Egg release – around 12 to 16 days before the start of the next menstrual period (in a typical 28-day cycle), the LH surge causes the mature follicle to rupture, releasing the egg into the Fallopian tube. This process is ovulation
- Egg journey – the released egg is then picked up by the fimbriae (finger-like projections) of the Fallopian tube and begins its journey toward the uterus. The egg is viable for fertilisation for about 12-24 hours after ovulation
Luteal phase
- Corpus luteum formation – after releasing the egg, the ruptured follicle transforms into the corpus luteum, which produces progesterone and some estrogen
- Uterine lining – progesterone helps to maintain the thickened uterine lining (endometrium) to support a potential implantation of a fertilised egg
If fertilisation occurs
- Implantation – if sperm fertilises the egg, the resulting embryo travels to the uterus and implants in the uterine lining. The corpus luteum continues to produce hormones to support early pregnancy.
If fertilisation does not occur
- Corpus luteum breakdown – if the egg is not fertilised, the corpus luteum degenerates, leading to a decrease in hormone levels
- Menstruation – the drop in progesterone triggers the shedding of the uterine lining, resulting in menstruation. The menstrual cycle then begins anew
Signs of ovulation
- Change in cervical mucus – the mucus becomes clearer, stretchier, and more slippery, resembling egg whites
- Basal body temperature – a slight increase in basal body temperature is observed after ovulation
- Ovulation pain – some women experience mild abdominal pain or discomfort known as Mittelschmerz during ovulation
- LH surge test – over-the-counter ovulation predictor kits detect the LH surge, indicating that ovulation is imminent
References
- Ovulation and conception. The Royal Women’s Hospital, Australia. Accessed 27 July 2024
- Ovulation and Fertility. Pregnancy, Birth and Baby, Australia. Accessed 27 July 2024
- Ovulation calculator. Office of Women’s Health, USA. Accessed 27 July 2024
- Right time for sex – when do you ovulate. Your Fertility, Australia. Accessed 27 July 2024
- The normal menstrual cycle and the control of ovulation. National Institutes of Health, USA. Accessed 27 July 2024
Last reviewed and updated: 27 July 2024
