While you may want it to be regular, the menstrual cycle is not always regular. Your menstrual cycle length might be different month-to-month. But some women’s periods are so regular that they can predict the day and time that they will start.
Your periods are said to be “regular” if they usually come every 24 to 38 days. The duration from the first day of your last period to the start of your next period should be at least 24 days but not more than 38 days.
Ovulation: What Is It?
There are about six days during each menstrual cycle when you can get pregnant. This is called your fertile window. You are most likely to get pregnant if you have sex without birth control in the three days before and up to the day of ovulation.
Ovulation is when the ovary releases an egg so it can be fertilized by a sperm in order to make a baby. A man’s sperm can live for three to five days in a woman’s reproductive organs. However, a woman’s egg lives for just 12 to 24 hours after ovulation. The time between ovulation and when the next period begins can be anywhere from one week (seven days) to more than two weeks (19 days).
Each woman’s cycle length is different. The typical cycle has three phases:
- Follicular (before release of the egg)
- Ovulatory (egg release)
- Luteal (after egg release)
Anovulation means a lack of ovulation or absent ovulation. When ovulation is irregular — but not completely absent — it is known as oligo-ovulation. Both anovulation and oligo-ovulation are types of ovulatory dysfunction. Late ovulation does not produce the best quality eggs, which can also reduce the likelihood of pregnancy.
During different times in your life, ovulation may or may not happen:
- Women who are pregnant do not ovulate.
- Women who are breastfeeding may or may not ovulate.
- During the transition to menopause (perimenopause), you may not ovulate every month.
After menopause, you do not ovulate.
What Causes Late Ovulation?
Luteinizing hormone (LH) is a hormone released by your brain that tells the ovary to release an egg. LH levels begin to increase about 36 hours and peak about 12 hours before ovulation, so your doctor may test for LH levels. When this happens later than the expected time, you experience late or delayed ovulation.
Reproduction is controlled by a system that includes the hypothalamus (an area of the brain), pituitary gland, ovaries, and other glands. When you have problems with ovulation, it is most likely due to any of the following malfunctions:
- Your hypothalamus may not secrete gonadotropin-releasing hormone, which stimulates the pituitary gland to produce the hormones that stimulate the ovaries and ovulation.
- Your pituitary gland may produce too little luteinizing hormone or follicle-stimulating hormone.
- Your ovaries may produce too little estrogen.
- Your pituitary gland may produce too much prolactin, a hormone that stimulates milk production. High levels of prolactin (hyperprolactinemia) may result in low levels of the hormones that stimulate ovulation.
- Other glands may malfunction. For instance, your adrenal glands may overproduce male hormones (such as testosterone), or the thyroid glands can overproduce or underproduce thyroid hormones.
Although late ovulation may be due to many disorders, the most common cause is polycystic ovary syndrome. It’s usually characterized by excess weight and the overproduction of male hormones by the ovaries. Your doctor may measure testosterone levels in the blood to check for polycystic ovary syndrome.
Other causes of late ovulation include:
- Excessive exercise
- Certain drugs (such as estrogens and progestins and antidepressants)
- Weight loss
- Psychological stress
Treating Late Ovulation
Medication. Your doctor may prescribe drugs, such as clomiphene or letrozole. Clomiphene is not effective for all causes of ovulation problems. It's most effective when the cause is polycystic ovary syndrome. Letrozole has fewer side effects than clomiphene. Your doctor may also prescribe metformin (a drug used to treat people with diabetes) usually with clomiphene, to stimulate ovulation.
Hormone therapy. Human gonadotropins contain follicle-stimulating hormone and sometimes luteinizing hormone. Your doctor will inject it into a muscle or under the skin.
If the cause of infertility is early menopause, neither clomiphene nor human gonadotropins can stimulate ovulation.
How to Know When You’re Ovulating
Knowing when you ovulate helps you plan for sex at the right time, thus improving your chance of getting pregnant. You can keep track of your menstrual cycles on a chart, in a diary, or on a free period-tracker app.
To determine if or when ovulation is occurring, your doctor may ask you to take your temperature before getting out of bed (basal body temperature) each day. Use a basal body temperature thermometer designed for women who are trying to become pregnant or a mercury thermometer. An increase of more than 0.9° F (0.5° C) in temperature usually indicates that ovulation has just occurred.
More accurate methods include an ovulation predictor kit, ultrasonography, and measurement of the level of progesterone in the blood or one of its by-products in the urine. An increase in levels of progesterone or its by-products indicates that ovulation has occurred.