How many weeks does pregnancy last and how can you calculate your due date?

How many weeks does pregnancy last? The answer to this question, simple in theory, is not that obvious!

Of course, it is assumed that pregnancy lasts 9 months, i.e., 40 weeks or 280 days. The due date can be easily calculated on a basis of the first day of the last menstruation in a pregnancy application or in an online calculator. However, only between 4 to 5% of mothers gives birth precisely at that time.

See how pregnancy progresses and learn while it is good to know the predicted due date!

Why does pregnancy last from the first day of the last period?

Are you at the very beginning of pregnancy and are only about to calculate your due date? If you plan to use a calculator available online or in a pregnancy application, you will quickly learn that everywhere you will have to provide the first day of your last period.

It is important because it is precisely the date assumed to be the beginning of pregnancy.

Are you wondering why then, if the actual conception occurs a few - several days later...? This is due to the fact that ovulation in women occurs at different times - depending on individual characteristics and/or the cycle length. Furthermore, not many of future Mums are able to precisely determine the date of baby’s conception. The date of the last period, on the other hand, is easy to provide and it is on this basis that it is assumed that the due date will occur after 40 weeks of pregnancy.

The due date based on an ultrasound scan and on the last menstruation - can they differ?

Did you know that during each obstetrics ultrasound scan a doctor will determine the pregnancy age on a basis of your baby’s parameters? It is also a basis for calculating the foreseen due date. Very rarely the due date based on the ultrasound scan and on the last period fall on the same day. Is it something bad?

As we have already said, the due date is calculated on a basis of the first day of the last period, and not the actual conception. For this reason, differences of a few or even (in decisively more rare cases) several days between foreseen due dates are nothing worrying.

The actual length of pregnancy is completely individual. In the case of multiple pregnancies and/or those ending with the caesarean section, the due date also frequently set at an earlier date. Then it is usually earlier than the foreseen due date, and the actual pregnancy duration is e.g., 38 or 39 weeks.

How can you calculate your due date yourself? The Naegele's formula

Did you know that there is a special formula for calculating your due date? According to the Naegele's formula, you deduce three months from the first day of your last period, and add one year and seven days.

What is important, this calculation only works for women having regular menstruation cycles of 28 days. When your cycles are longer, to the obtained result add the number of days by which your cycles differ from 28 days. If your cycles are shorter than 28 days, then deduce the difference between 28 and the length of your cycle from the result.

How long does pregnancy last?

The pregnancy lasts 280 days. Is this long or short? This is possibly associated with women’s metabolism. A body of a mother expecting a baby has a strength to generate enough energy to maintain pregnancy for about nine months. For this reason, pregnancy lasts 40 weeks, and the delivery between 38 and 42 pregnancy week is considered to be “correct” or “on time”.

In some sources, you can also find information that pregnancy actually lasts 38 weeks, i.e., about 267 days. What is a cause of these differences? Some studies simply calculate the pregnancy duration from the moment of the actual conception.

The number of weeks that a given pregnancy lasts depend on various factors. The most important are, of course, the health of the mum and her baby.

Pregnancy breaking up into trimesters

As we have already mentioned, pregnancy lasts 40 weeks, that are broken into three trimesters.

The first pregnancy trimesters lasts until the end of the 13th pregnancy week. The second pregnancy trimester begins with the beginning of the 14th pregnancy week and lasts until the end of the 27th pregnancy week. The last, third trimester begins with the beginning of the 28th pregnancy week and lasts until labour.

The first trimester is the time of rapid changes in the woman’s body and of initial phases of the baby’s development. Already at this stage, many serious genetic diseases can be ruled out. In this period, women also experience first signs of pregnancy.

The second trimester is a time of the intense baby’s development and the best time for the majority of women. Then future mums have the greatest energy and strength. At that time also women start go get ready for labour at antenatal classes.

The third trimester is the best time for future mums for last preparations for “zero hour”. Then they complete the layette, pack their hospital bag, and visit their gynaecologist more frequently than before.

Pregnancy breaking up into weeks

The normal length of pregnancy is 40 weeks, but actually women learn that they are pregnant in 4th or 5th week. This results from the fact that then most “sensitive” tests can determine pregnancy.

The end of pregnancy is usually independent of a due date. When pregnancy ends naturally, and progresses in a physiological way, without a need to initiate labour, then it will occur when your baby is ready for it. It is never fully known how much time will pass between the moment of conception and the baby’s arrival.

Install a pregnancy application and follow your pregnancy week by week!

How does pregnancy look like, week by week? If you like to know precisely what happens to your baby, you should install a pregnancy application on your phone!

Applications, such as HiMommy, have numerous functionality. They include:

calculation of the pregnancy age;

a base of knowledge on subjects related to the mother and the baby (e.g., which tests and examinations should be performed in which week, measurements and weight of your baby at different stages of its development, etc.),

a counter of contractions and kicks,

nutrition and layette lists.

See the options offered by the HiMommy application, which will provide you with a wealth of knowledge about your baby!