By Iván Ferrer Durbà BSc (biologist & science teacher).
Last Update: 03/16/2015

Ovulation usually happens during the days that coincide with half of the menstrual cycle. It doesn’t always have to be like this, though. During a very short menstrual cycle, ovulation and menstruation can happen almost at the same time, confusing thus the woman.

Some women tend to confuse an early bleeding with a regular period as well. An early bleeding happens when blood stains appear between periods. This early bleeding may occur at the same time as the moment of ovulation, which may lead to confusion.

If a woman thinks she’s menstruating, that is to say, she’s in the less fertile period of her cycle, the chances of pregnancy increase. In such cases, it is said that a woman got pregnant during her period when she was actually ovulating and not menstruating.

Calculating the ovulation date

Natural methods of menstrual cycle control are not often effective because ovulation does not always happen at the same time in every cycle. These methods are based on the idea that ovulation can be predicted. Apparently, measuring hormones in the blood is not enough to predict the female reproductive system status.

Theoretically, ovulation happens on the 14th day of the cycle. The first day of menstruation is considered the first day of the cycle. However, some women ovulate either before of after the 14th day so we cannot talk about a general method of calculating ovulation. This method would have to take into account every woman’s cycle’s length, external variations that can affect ovulation, the number of ovulations per cycle, etc.

Furthermore, an article published by the Fertility and Sterility magazine has announced that, sometimes, women ovulate several times in a month. One of those ovulations might coincide with menstruation, altering the fertility calendar and leading thus to a pregnancy.

This might explain the birth of twins conceived in different days.

Ovulation and menstruation are not the same

According to traditional medical science, women have cycles of about 28 days. During the cycle, ovarian follicles grow and develop but only one is able to burst and release a mature egg during ovulation. Once the egg is released, it falls inside the Fallopian tubes, where it will remain alive for 24 hours while waiting to be fertilized.

If, during those 24 hours, no spermatozoid is able to reach the Fallopian tubes and fertilize the oocyte, it will be discarded during menstruation, which is the endometrial shedding in the form of bleeding.

It is clear that, although hormonally related to each other, ovulation and menstruation are not the same:

  • Uterus: it grows during the cycle, waiting for the embryo implantation. If there’s no implantation, it sheds in the form of a bleeding called menstruation.
  • Ovary: follicles grow in the ovary and one of them will either be fertilized or discarded. If fertilized, the follicle receives the name of corpus luteum and releases hormones that maintain the endometrium, so the embryo can implant itself. If the egg is not fertilized, the corpus luteum doesn’t release hormones and the endometrium starts shedding. This leads to egg shedding.
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Authors and contributors

 Iván Ferrer Durbà
BSc
Biologist & Science Teacher
Bachelor's Degree in Biology by the University of Valencia (UV). Postgraduate Course in Secondary Education and Teaching by the University of Portsmouth. Teacher of Sciences at multiple British schools and high schools. More information
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