The calculation of conception: how it is done

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Catherine Le Nevez
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How the day of conception is calculated

There are many tools on the internet and applications that can be downloaded on smartphones that, by entering the date of the last menstruation, allow you to calculate what week of pregnancy you are in and when the birth will presumably take place.

Also on you can calculate at what week of pregnancy you are and the expected date of birth


From conception to the first minutes of life (PHOTO)

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From the encounter between that single sperm and an egg up to nine months later. The journey of life taken in pictures. Between growth and small, big progress.

To be more precise, however, for calculate the date of conception it is not enough just to refer to amenorrhea, but it is also necessary to know how long a woman's cycle lasts on average. "Ovulation occurs exactly 14 days before the next menstruation" explains Anna Franca Cavaliere, gynecologist at the Gemelli Hospital in the city. "This means that if the woman has a regular cycle of 28 days, ovulation - and therefore conception - will have occurred in the middle of the cycle; if, on the other hand, the cycle is 21 days, conception will have occurred about 7 days after the last one. menstruation, as well as if the cycles are long, of 40-45 days, the date of conception will be approximately one month after the last menstruation ".

Confirmation of the date of conception occurs with the first ultrasound

For this reason obstetric calculators only provide a calculation of the epoch of amenorrhea and not of pregnancy. Confirmation of dating can only be obtained with the first ultrasound - especially if it is performed between 10 and 14 weeks - during which the cranio-caudal length of the fetus is measured and, based on standard reference measurements available to the gynecologist , it will be possible to say with much more accuracy when the baby was conceived, at what gestational period the future mother is and when the term of pregnancy is expected.

(Read all about the first ultrasound)


This is how life is born - PHOTO

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Conception really has something magical about it. It is a complex process, in which everything must take place in precise sequences and with perfect mechanisms. It seems incredible that all this could ...

The calculation can be more accurate if you have targeted reports

Apart from the ultrasound, an accurate calculation can be made even if the couple has performed a ovulation monitoring and had targeted relationships in the days of ovulation: in this case you will know with certainty which were the fertile days and when the baby was conceived.

Consult the services of MyModernParents to cope well with pregnancy:

  • Calculate your pregnancy week 
  • Calculate the estimated date of delivery online
  • Calculate the length of the fetus
  • Mammenellarete blog: here you can read many stories about pregnancy

Pregnancy, all that happens in 40 weeks

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How does a baby develop inside his mother's body week after week? Being able to observe the miracle of life that is born and grows is an experience ...

Watch the pregnancy video series A look into the baby bump

  • conception calculation
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  • weeks 1-13
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