Ovulation is the release of an egg during menstruation in females. Part of the ovary called the ovarian follicle discharges an egg. The egg, also called ovum, oocyte, or female gamete. It is only released after it matures.
After the egg is released, it travels down the fallopian tube where it may be met by a sperm for fertilization to occur.
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A part of the brain called the hypothalamus controls ovulation and hormonal release during the menstrual cycle. It sends signals instructing the anterior lobe and pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Women trying to get pregnant should know when they are most likely to ovulate.
Phases of Ovulation
The ovulation process is defined by a period of elevated hormones during the menstrual cycle. It can be divided into 3 phases:
- The periovulatory or follicular phase: A layer of cells around the ovum starts to become more like mucus, and expand. The uterus lining then starts to thicken.
- The ovulatory phase: In this phase, enzymes are secreted and form a hole, or stigma. The ovum and its network of cells use the stigma to move into the fallopian tube. This is the period of fertility and usually lasts from 24 to 48 hours.
- The postovulatory or luteal phase: In the phase, LH is secreted. A fertilized egg will be implanted into the womb, while an unfertilized egg slowly stops producing hormones and liquefies within 24 hours.
The lining of the uterus also begins to break down and prepares to exit the body during menstruation.
When does ovulation occur?
A woman’s menstrual cycle lasts on average between 28 and 32 days.
The commencement of each cycle is considered to be the first day of the menses. Release of the egg generally occurs 12 to 16 days before the next period is due.
Most women begin to menstruate between the ages of 10 to 15 years. At the same time, they begin to ovulate and become able to get pregnant. This is a time referred to as the menarche.
Ovulation typically stops after menopause, between the ages of around 50 to 51 years on average, but it still occurs in the time leading up to menopause. This is referred to as perimenopause.
How to detect ovulation
There are several indications that a woman is ovulating.
During ovulation, the cervical mucus increases in volume and becomes thicker due to increased levels of estrogen. The cervical mucus is sometimes likened to egg whites at a woman’s most fertile point.
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There may also be a slight increase in the temperature of the body. This is driven by the hormone progesterone, which is secreted when an egg is released. Women are generally most fertile for 2 to 3 days before the temperature reaches its maximum.
A basal thermometer can be used to track the slight temperature increase. Some women feel a mild ache or pang of pain in the lower abdomen, a condition called Mittelschmerz pain. It may last between a few minutes and a few hours.
Finally, ovulation predictor kits, available from drug stores, can detect the increase in luteinizing hormone (LH) in the urine just before ovulation.
The ovulation calendar is designed to help a woman predict when she will be most fertile to achieve pregnancy. It is generally useful for women to record or chart menstrual information for entry into the calendar. Keeping track of the menstrual cycle can also vital for highlighting any abnormalities.
Disorders linked to ovulation
Issues with the ovulation process can lead to infertility.
Polycystic ovarian syndrome
A woman with polycystic ovarian syndrome (PCOS) has enlarged ovaries, often with small, fluid-filled cysts on them. It can lead to a hormone imbalance that can disrupt ovulation. Other symptoms can include obesity, abnormal hair growth, insulin resistance, and acne.
This happens when the production of the FSH and LH hormones is interrupted. These are the hormones that stimulate ovulation. This can affect the menstrual cycle. Irregular menstrual cycles are common.
Causes of hypothalamic dysfunction may include excessive physical or emotional stress, very high or low body weight, or substantial weight gains or losses.
Excessive exercise, low body weight, and tumors of the hypothalamus can also lead to hypothalamic dysfunction.
Premature ovarian insufficiency
This condition occurs when egg production stops prematurely, due to a drop in estrogen levels. It can be due to an autoimmune disease, genetic abnormalities, or environmental toxins. It affects women before the age of 40 years.
Hyperprolactinemia, or excess prolactin
In certain situations, such as the use of medication or an abnormality in the pituitary gland, which produces hormones, women can produce excessive amounts of prolactin.
This, in turn, can cause a reduction in estrogen production.
Excess prolactin is a less common cause of ovulatory dysfunction.
Ovulation can be induced by fertility drugs.
These medications are known to regulate or trigger ovulation. Doctors may prescribe the following to treat anovulation, or the cessation of ovulation.
Brand names are included in brackets.
- Clomiphene citrate (Clomid):This oral medication increases pituitary secretion of FSH and LH, stimulating ovarian follicles.
- Letrozole (Femara):This works by temporarily lowering a woman’s level of the hormone progesterone to stimulate ovum production.
- Human menopausal gonadotropin or hMG (Repronex, Menopur, Pergonal) and FSH (Gonal-F, Follistim):These injectable medications are known as gonadotropins and stimulate the ovary to produce several eggs for ovulation.
- Human chorionic gonadotropin or hCG (Profasi, Pregnyl):This matures eggs and subsequently triggers their release during ovulation.
- Metformin (Glucophage):This medication is typically used in women with PCOS to treat insulin resistance and increase the chances of ovulation.
- Bromocriptine (Parlodel) and Cabergoline (Dostinex):These medications are used in cases of hyperprolactinemia.
Be aware that taking fertility drugs can increase your chances of having twins or triplets. The above may trigger side effects, including:
- abdominal pain
- hot flushes
- mood swings
- vaginal dryness
- heavy menstrual flow
- tenderness in the breasts
- increased urination
If these become severe, a doctor may be able to suggest other options.
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