People can get pregnant at any time during their menstrual cycle, though it is much less likely during their period.

A person is most likely to get pregnant in the middle of their menstrual cycle. This phase is the fertile window.

The chances of becoming pregnant are much lower before and after the fertile window, but it is still possible, and there are several factors to consider.

In this article, we look at the chances of becoming pregnant during the period and at other times of the menstrual cycle.

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A person can become pregnant at any time. However, it is most likely around the time of ovulation.

The average menstrual cycle is 28 days. The menstrual cycle is the time between the first day of one period and the first day of the next period. Ovulation usually occurs 12-14 days after a person’s period ends.

During ovulation, the egg leaves the ovary and travels down the fallopian tube, where sperm can fertilize it. The egg can only survive for 24 hours after ovulation. For this reason, it must meet a sperm cell during this time for pregnancy to occur. The egg then travels to the uterus.

According to a 2018 study, a person is most likely to get pregnant between the 8th and 13th day of the menstrual cycle. This means that the likelihood of a person becoming pregnant during their period is low.

However, it is not quite as simple as this due to three main factors:

  • a person’s menstrual cycle length
  • monthly differences in the timing of ovulation
  • how long sperm stay alive inside the body

Cycle length

Menstrual cycles are still “normal” if the period comes every 21–35 days, so cycle length varies significantly between people. People with shorter menstrual cycles may ovulate closer to their period than people with longer cycles.

Ovulation timing

The wide variation in menstrual cycle length and the timing of ovulation makes it difficult to tell when a person is in their fertile period.

Some research suggests that having sexual intercourse on the day before ovulation will carry the same chances of getting pregnant as having sexual intercourse multiple random times throughout the menstrual cycle.

The role of sperm

On top of this, sperm can live for 3–5 days inside a body, which means that a person can get pregnant even if they have sexual intercourse 5 days before ovulating.

So, although it is possible to become pregnant during the period, it is unlikely.

The fertile window usually occurs in the middle of a person’s cycle. This window lasts a few days before ovulation and ends a day after ovulation. People are most likely to become pregnant during this time.

Due to this, people are less likely to get pregnant in the days leading up to their period. This is especially true if their periods are regular and they have a 28-day menstrual cycle.

It is, however, possible for a person to get pregnant immediately after their period. This is because sperm can still fertilize eggs for up to 7 days after sexual intercourse.

If a person with a short cycle has sexual intercourse right after their period and ovulates early, they may ovulate quickly enough for the egg to connect with sperm cells.

While many people ovulate regularly from the time they start their period until menopause, this is not always the case. A person’s menstrual cycle may vary in length and regularity throughout their lifetime, and ovulation wihin their cycle may also change. It is also common for ovulation to become irregular in perimenopause. This is the period before menopause.

The following factors can contribute to irregular ovulation timings and periods:

People can keep track of their ovulation days using the following tools:

  • making use of free fertility charts
  • taking their body temperature at rest every day and looking for slight upticks that could indicate ovulation
  • using fertility monitors to check for luteinizing hormone surges
  • using smartphone apps, which may or may not have faced scientific evaluation

Given the fluid nature of the fertile window, people who do not want to become pregnant should still use contraception at this time. Combination control pills stop ovulation and, therefore, the ability to get pregnant.

Some contraceptive medications can alter the regularity of a person’s period or stop it altogether.

Although a person can get pregnant during their period, it is unlikely.

The chances of becoming pregnant on or just after the period end depend on when a person has sexual intercourse, the length of their menstrual cycle, and the exact day they ovulate during that menstrual cycle.

These factors make it hard to predict the precise timing and extent of the fertile window.

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