Fertilization is the union of male sperm and female egg.
Fertilization is the union of male sperm and female egg.

Fertilization is the union of male sperm and female egg. In other words, fertilization is an event that occurs when a single sperm enters a mature egg, releasing its genetic material into that egg. This triggers two sets of deoxyribonucleic acid (DNA) to combine forming a potential baby (human zygote). It is more of a chain of events than a single, isolated phenomenon:

  • Fertilization generally occurs in a fallopian tube (uterine tubes).
  • When sperms enter the vagina during sexual intercourse, they swim through the female’s womb and into a fallopian tube.
  • Although millions of sperm are present, only a few hundred are likely to reach the egg, and only a single sperm will enter the ovum.
  • When a sperm finally breaks through the egg’s cell membrane, it sets off a reaction that prevents other sperms from entering.
  • After the sperm penetrates the egg, the tail falls off and its nucleus fuses with the nucleus of the egg.
  • The resulting zygote contains all the chromosomes needed for a new individual. 
  • Half the chromosomes are from the egg, and half are from the sperm.
  • Indeed, interruption of any step in the chain may cause fertilization failure.
  • Successful fertilization requires not only that a sperm and egg fuse but also that not more than one sperm fuses with the egg.
  • The process of human fertilization is very complicated and comprises many steps and components necessary to achieve the ultimate result of human life.

How long after a positive ovulation test are you fertile?

It should not take less than 60 to 65 hours to conceive. A woman may only have about 60 hours or less than 2½ days during the cycle when conception is possible. Once the egg dies, women may no longer be fertile, and their period will come to start the next cycle. Eggs are only viable for about 24 hours once released. If combined with the 36 hours between a positive ovulation test and ovulation, which comes down to less than 60 hours. This is because sperm can survive inside the cervix for up to 5 days; if the fertile cervical mucus is present, having intercourse before ovulation occurs can ensure sperm is waiting for the egg, giving the egg a higher chance of fertilization.

Why should women calendar their most fertile days?

Calculating and calendaring the most fertile days may help in the best fertilization chances. Ovulation calculators and calendars are tools that attempt to predict when women might ovulate. These tools are based on the typical length of their menstrual cycle and the expected window for ovulation. These tools will guide a woman when they are releasing an egg each month (also known as ovulating), and when they are the most fertile for the best chances of getting pregnant. Likewise, if they are taking any fertility medications, these tools can be used to suggest when they may be the most fertile for sexual intercourse. 

To use an ovulation calculator, a woman should know the following:

  • Their first day of the last menstrual cycle
  • Number of days they have a menstrual cycle
  • The number of days in their luteal phase: This is the latter phase of the menstrual cycle starting from ovulation and ending on the first day of your next cycle. While the amount of time before ovulation can vary widely each month, the time after ovulation to the end of your cycle is usually fairly constant, and unless you have a health problem that affects your periods, this phase is 14-16 days. If a woman is not sure about the length of the luteal phase, they can assume it is 14 days (the average length for most women).

Charting in ovulation and calendaring may not be perfect, but they may be accurate. In addition, the results may not be right if a woman is not sure about their last menstrual period, or if they have irregular cycles. The calculators can give an idea about likely ovulation time. Combining the two may be beneficial. These tools are based on averages, and even if women may be charting periods accurately, cycle length and ovulation date may vary from cycle to cycle. These tools are the most beneficial to women having regular periods by calculating average cycle length and allowing them a wider fertility window to conceive.


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Medically Reviewed on 3/12/2021
Fertilization: https://www.ncbi.nlm.nih.gov/books/NBK26843/

Ovulation Calculator: https://www.webmd.com/baby/healthtool-ovulation-calculator