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Understanding Ovulation and Fertile Period

What is Ovulation ?

Understanding the Ovulation cycle, fertile period and most fertile days in a menstrual cycle greatly improves the chances of getting pregnant. Ovulation is the name of the process that happens usually once in every menstrual cycle when hormone changes trigger an ovary to release an egg. After release, the egg travels down the fallopian tube, where it may be met by a sperm and become fertilized. It is useful to know when ovulation is likely to occur, as a woman is most fertile during this period, and more likely to conceive.

What happens during Menstrual Cycle ? Ovulation Calculator Ovulation Calendar

In the first half of the cycle, levels of estrogen start to rise, and makes the lining of the uterus (womb) grow and thicken. At the same time an egg, or ovum, in one of the ovaries starts to mature. At about day 14 of an average 28-day cycle, the egg leaves the ovary. This is called ovulation.
After the egg has left the ovary, it travels through the fallopian tube to the uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the 3 days before or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate before or after day 14.
A woman becomes pregnant if the egg is fertilized by a man’s sperm cell and attaches to the uterine wall. If the egg is not fertilized, it will break apart. Then, hormone levels drop, and the thickened lining of the uterus is shed during the menstrual period.

What happens during 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 begins to mucify, or become more like mucus, and expand. The uterus lining begins to thicken.
  • The ovulatory phase: Enzymes are secreted and form a hole, or stigma on the ovary. 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: LH is secreted. A fertilized egg will be implanted into the womb, while an unfertilized egg slowly stops producing hormones and dissolves within 24 hours.

How do I calculate when I am ovulating ?

  • 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 conceive. 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 peri-menopause.
  • A menstrual cycle is defined from the first day of menstrual bleeding (called day 1) of one menstrual period to the first day of menstrual bleeding of the next.
  • A woman’s cycle lasts on average between 28 and 32 days. Some women may have much shorter or much longer cycles.
  • Release of the egg generally occurs 12 to 16 days before the next period is due.
  • Ovulation can be calculated by starting with the first day of the last menstrual period (LMP) or by calculating 12-16 days from the next expected period.
  • Most women ovulate anywhere between Day 11 – Day 21 of their cycle, counting from the first day of the LMP.
    This is what many refer to as the “fertile period” of a woman’s cycle because sexual intercourse during this time increases the chance of pregnancy.
  • For most women ovulation is likely to happen around the middle of the cycle. However there is lot of variability in length of menstrual cycle among women, and with in cycles in same individual. Even in women with fairly regular cycles the day of ovulation can vary by +- 3 days.
  • It is important to track your cycle and you may use Ovulation Calculator to help identify peak fertile days.
  • Ovulation Calculator on this web site uses the results from multiple studies and precisely calculates the chances of ovulation on each day of the cycle. It gives you range of days in which you are most likely to ovulate. The chances of ovulation are high in the middle of this range and low near start and end days of this range.

Don’t women ovulate on the 14th day after their period starts ?

Unfortunately, this is a myth that many, including healthcare professionals, still believe. The “14th-day” thinking appears to come from either taking the average of when all women ovulate or from just dividing the 28-day cycle in half. This is not an accurate way to calculate ovulation because many women do NOT ovulate on the 14th day of their cycle.
The day of ovulation differs from woman to woman and can even be different from month to month for an individual woman. For a woman with a 28-day cycle, the window of ovulation is day 11 through day 21 of your cycle. Ovulation could occur on any one day during this window.

Do you know…

That most of the online ovulation calculators and fertility apps are often wrong or misleading?

Internet is littered with many ovulation tracker or fertility applications. But will you believe that most of these are often wrong or misleading. Here is a simple litmus test. We know that WHO (World Health Organization), recommends the Standard Days Method or SDM as a viable method of contraception having effectiveness of 95% when used correctly. Standard days method is recommended for women who have cycle length between 26 to 32 days. SDM recommends days 8 to 19 of a women’s mensural cycle as fertile period.

Most of the fertility apps determine a woman’s fertile window based on the assumption that ovulation happens on 14th day of the cycle and most fertile days are the ovulation date and the five preceding days. So out of total 12 potentially fertile days many couples could be missing critical opportunities for conception each month. For some, the added stress and frustration of months of unsuccessful attempts could be due in part to these false assumptions.

Now if you try our Advanced Ovulation Calculator with cycle length of 28 days, it will identify a fertile period of 10 days from day 9 to day 18 of the cycle. To be more accurate there are chances of conception on day 8 and 19 also, which we have intentionally excluded, because on these days the chances of conception are very low about less than 2%. This clearly indicates that our application is much more precise and accurate.

Women who want to use our calculator for getting pregnant can follow the fertility period identified in the results. However, women who want to use it as contraception tool may also add one day on each side in the days to avoid intercourse.

How can ovulation be detected ? Best Ovulation Calculator Ovulation Calendar

There are several indications that a woman is ovulating.

  • During ovulation, the cervical mucus increases in volume and becomes thicker due to increased estrogen levels. The cervical mucus is sometimes likened to egg whites at a woman’s most fertile point.
  • There may also be a slight increase in body temperature. 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 subtle temperature increase. These can be purchased online or at most drug stores.
  • Some women feel a mild ache or pang of pain in the lower abdomen. This is 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.

What are most fertile days in menstrual cycle ?

An egg can survive in the Fallopian tube for about 24 hours after ovulation. A man’s sperm can survive inside a woman’s body for about 3 days (and sometimes up to 5 days) after sexual intercourse. You can become pregnant if you have sex anywhere from 5 days before ovulation until 1 day after ovulation. Your chance of pregnancy is highest when live sperm are present in the fallopian tubes when ovulation occurs.

Can I have a period and still not have ovulated ?

Having a period does not necessarily mean that ovulation has taken place. Some women may have what is called an anovulatory cycle, (meaning ovulation has not occurred). During an anovulatory cycle, women may experience some bleeding which may appear to be a period, although this is actually not a true period.
This bleeding is caused by either a buildup in the uterine lining that can no longer sustain itself or by a drop in estrogen. The main way to decipher if ovulation is, in fact, taking place is by tracking your basal body temperature, and by transvaginal ultrasound.


Dr Sobia Mohyuddin

MCPS, FCPS, MRCOG, Consultant Obstetrics & Gynaecology

Doctor Sobia Mohyuddin is a highly skilled and experienced Obstetrician and Gynecologist, with 25 years of training and experience in renowned, large institutions. She holds the position of Associate Professor and Fellow at the College of Physicians and Surgeons Pakistan. She is also a member of the Royal College of Obstetricians and Gynecologists (UK).

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