How many weeks does pregnancy last?

How many weeks does pregnancy last?
Fonte: shutterstock

How many weeks does pregnancy last

Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period. But why is it commonly said that pregnancy lasts 9 months? And how is the expected date of birth calculated by counting the corresponding weeks and months? Here's everything you need to know and how many weeks does the pregnancy last.

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How many weeks are 9 months?

Precise 9 months correspond to just over 39 settimane. But pregnancy is not calculated in months, but in weeks: on average a gestation it lasts 280 days, that is 40 weeks. 

Read also: Pregnancy, duration

Week of pregnancy calculation table

To calculate the weeks of pregnancy and the expected date of delivery, doctors use a tool called a ruler (starting from the day of the last menstruation) or apply Naegele's rule: add seven days and subtract three months from this date.

Here is a table quite accurate of the weeks of pregnancy.

  • First week of pregnancy
  • Second week of pregnancy
  • Third week of pregnancy
  • Fourth week of pregnancy
  • Fifth week of pregnancy
  • Sixth week of pregnancy
  • Seventh week of pregnancy
  • Eighth week of pregnancy
  • Ninth week of pregnancy
  • XNUMXth week of pregnancy
  • Eleventh week of pregnancy
  • Twelfth 12th week of pregnancy
  • Thirteenth week of pregnancy
  • Fourteenth week of pregnancy
  • Fifteenth week of pregnancy
  • 16th XNUMXth week of pregnancy
  • Seventeenth week of pregnancy
  • Eighteenth week of pregnancy
  • Nineteenth week of pregnancy
  • Twentieth week of pregnancy
  • Twenty-first week of pregnancy
  • Twenty-second week of pregnancy
  • Twenty-third week of pregnancy
  • Twenty-fourth week of pregnancy
  • Twenty-fifth week of pregnancy
  • Twenty-sixth week of pregnancy
  • Twenty-seventh week of pregnancy
  • Twenty-eighth week of pregnancy
  • Twenty-ninth week of pregnancy
  • Thirtieth week of pregnancy
  • Thirty-first week of pregnancy
  • Thirty-second week of pregnancy
  • Thirty-third week of pregnancy
  • Thirty-fourth week of pregnancy
  • Thirty-fifth week of pregnancy
  • Thirty-sixth week of pregnancy
  • Thirty-seventh week of pregnancy
  • Thirty-eighth week of pregnancy
  • Thirty-ninth week of pregnancy
  • Forty week of pregnancy

If you want to do a pregnancy week calculation and if you don't remember what week you are, use our calculator to find out where you are in your pregnancy and when your baby is born: just enter the date of your last menstruation and the average length of your cycle to get the information you need.

Calculation date of birth and weeks of pregnancy

The pregnancy lasts an average of 40 weeks, i.e. 280 days, that is about 9 months. However, sometimes it is not thought that, to count the weeks of pregnancy, one starts from the date of last menstruation (i.e. the first day of the last cycle). This count is called gestational age and its reason is obvious: the date of the last menstruation, except for sudden amnesia, is easily remembered and, consequently, the accounts are more precise.

But if we wanted to look at the exact age of the fetus, then we would have to start the account from the date of conception (i.e. the moment when the egg cell is fertilized by a sperm). In this case, we would speak of conception age, which is the true age of the child. In practice, however, this method cannot be used, due to the obvious difficulty in reconstructing the exact day of conception (which depends on both the date of intercourse and the date of ovulation, which is difficult to determine).

So summarizing:

  • Gestational age: it is calculated starting from the first day of the last menstruation had before discovering that you are pregnant. It is based on a precise calculation but it is not the true age of the baby, but only the conventional "duration" of the pregnancy. However, it is the gestational age that is used by all professionals, ie gynecologists and obstetricians
  • Conception age: it is calculated from the moment of conception and therefore materially it is an impossible or in any case imprecise calculation, but it would allow us to know the true age of our child. So the pregnancy really lasts 40 weeks, with a possible fluctuation of more or less two weeks, perfectly normal.

Months of pregnancy | PHOTO

Photos of pregnancy month by month. Images of the belly and fetus from the first month to the ninth month of pregnancy

At how many weeks can you give birth without risk to the baby?

Il premature birth it is classified in various ways according to the gestational age in which it is found. We talk about:

  • late premature birth if the baby is born between the 34th and 37th week of pregnancy,
  • severe preterm labor if the birth occurs between the 25th and the 33rd week of pregnancy,
  • extreme premature birth if the baby is born before the 25th week of gestation.

The closer you get to the estimated date of delivery, the more likely your baby will be without problems or complications and may even be left out of the incubator. Of course, babies born very premature are not ready for extrauterine life and will require neonatal intensive care. 

Calculation of weeks of pregnancy and months correspondence

This is how the pregnancy month by month.

  • first month of pregnancy
  • second month of pregnancy
  • third month of pregnancy
  • fourth month of pregnancy
  • fifth month of pregnancy
  • sixth month of pregnancy
  • seventh month of pregnancy
  • eighth month of pregnancy
  • ninth month of pregnancy

Table of months of pregnancy and corresponding weeks

1st month: from the 1st day of the last menstruation to 4 weeks + 3 days
2nd month: from 4 weeks + 4 days to 8 weeks + 5 days
3rd month: from 8 weeks + 6 days to 13 weeks + 1 day
4nd month: from 13 weeks + 2 days to 17 weeks + 4 days
5nd month: from 17 weeks + 5 days to 21 weeks + 6 days
6nd month: from 22 weeks + 0 days to 26 weeks + 2 days
7nd month: from 26 weeks + 3 days to 30 weeks + 4 days
8nd month: from 30 weeks + 5 days to 35 weeks + 0 days
9th month: from 35 weeks + 1 day to 40 weeks + 0 days

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