How many weeks pregnancy lasts in women: obstetric calculations and the correct timing. How many weeks does a pregnancy normally last? How many weeks is the pregnancy from the day of conception

How long does pregnancy last? Pregnancy lasts 6500 hours, or 280 days, nine months, or 10 obstetric months.

The determination of gestational age and due date is based on the assumption that a woman has a 28-day menstrual cycle with ovulation on days 14–15 of the cycle. Pregnancy lasts an average of 280 days (40 weeks) from the start of the last menstrual period. There are 4 weeks or 28 days in the obstetric month. Therefore, the duration of a normal pregnancy is 10 obstetric months. However, 280 days is the conventional number of days of pregnancy. Determining the true gestational age is difficult due to the fact that it is difficult to establish the exact period of ovulation, the time of movement of spermatozoa and fertilization, it is difficult to take into account all the characteristics of a woman’s body and predict the time when a baby is “ready” for birth. Therefore, a baby is considered full-term if it is born between 266 and 294 days (38-42 weeks) of pregnancy.

Video: Calculate the gestational age in weeks

For example:

Pregnancy in cats lasts from 58 to 72 days.

Pregnancy in dogs lasts from 56 to 72 days.

Pregnancy in elephants lasts 22-23 months.

After learning about her pregnancy, every woman begins to calculate the days and weeks to determine the possible date of delivery. The doctor who leads the pregnancy also helps her in this.

Of course, no one can guarantee that a child will be born on a particular day, because even if you know with absolute certainty the time of conception of your baby, it is completely unknown how and how much he will grow and develop in his mother's belly before deciding to appear into the world.

(PDR) depends on many different factors, and in each case its calculation is very individual.

How many weeks does pregnancy last from the day of conception: why is there a difference in timing?

Pregnancy is known to last nine months. However, if we compare this period with the calculation of the DA in weeks, it becomes quite obvious that they differ, because nine months is only thirty-six weeks, and not forty or forty-two, as doctors believe. How can such a difference be explained?

There is the concept of "gold obstetric standard" or obstetric gestational age. It is determined based on the duration of the menstrual cycle and ovulation.

The average cycle duration is taken into account - twenty-eight days with egg maturation or ovulation in the middle (by the way, the obstetric month also lasts twenty-eight days, unlike the calendar one, lasting thirty or thirty-one days).

The conditional number of days from conception to childbirth, according to this method of calculation, will be two hundred and eighty, that is, forty full weeks.

Doctors talk about the conventions of these numbers, because it is almost impossible to predict, even with the exact time of ovulation, how soon the spermatozoa reached the goal, and when exactly the fertilization of the egg occurred. Do not forget that the speed of advancement of an already fertilized egg through the fallopian tubes before implantation in the uterine wall can also be different.

How can I calculate the gestational age: the main methods for determining

There are several ways to help calculate the duration of pregnancy and set the expected date of birth.

• obstetric method.

The most common is obstetric.

The main number from which the countdown is based is the date your last period started. For this, the Negele formula is used, according to which, nine full months and one week are added to the date of the last menstruation.

An even simpler calculation can be made if three full months are subtracted from the same date and one week is also added.

This is how the age of pregnancy is calculated, but not conception, since there was no pregnancy at the time of the start of menstruation, that is, with a 40-week calendar, actual conception occurs only in the third week (after all, ovulation can occur on average on the fourteenth to fifteenth day after menstruation has ended), which means that the gestational age of the child will be approximately two to three weeks less.

• embryonic method.

If you know exactly not only the day and time of conception, but also the day and time of egg maturation, then you can use the embryonic method of calculating the date of birth and determining the duration of pregnancy.

Usually, average figure will be about two hundred and sixty-six days or thirty-eight weeks. But this method has almost no application, because few future mothers will be able to tell the doctor this data.

When calculating the obstetric gestational age, they usually take into account only the average duration of the menstrual cycle with ovulation in the middle (on the fourteenth to fifteenth day).

Therefore, if you suffer from irregular periods, cycle failures, or if it lasts more or less than twenty-eight days, you will have to take into account all these nuances (if your cycle is longer, then add the required number of days to the proposed calculation, and if less, subtract) .

In addition, at a later date, the expected date of birth is also determined by:

• is a highly inaccurate and unreliable method.

It is believed that if a woman is carrying her first child, then five months (full obstetric) must be added to the date when she felt his first stirring in her stomach, and if the pregnancy is not the first, then five and a half, because the first movements can usually be felt in the twentieth to twenty-second week, and for the second - somewhere in the eighteenth.

This will give you the approximate duration of your pregnancy and the date of your future birth. However, these numbers will be very relative, because many women do not immediately recognize the baby's movements, confuse them with contractions or intestinal motility, moreover, everything is very individual.

• From the second trimester (fourteen to sixteen weeks) onwards, the doctor will be able to give approximate dates, based on a routine examination, and (there are special fixed norms for each specific period of pregnancy).
• It also helps in the calculations and - based on clear parameters, such as CTE, head and tummy circumference, bone length and others, the doctor can determine not only the gestational age, but also the gestational age of the baby with an accuracy of three days.

However, all these are rather auxiliary and additional options, in addition to the two main ones.

Duration of pregnancy and norms - no more and no less

Of course, the estimated date of birth is therefore called the estimated date, because the child cannot and should not be born exactly by the hour on the date you calculated.

Normal natural childbirth usually occurs between thirty-eight and forty-two weeks. It was at this time that pregnancy is considered full-term, because all the main organs and systems of the child have developed and matured, so that he becomes ready to be born. To date, however, the period has been extended from thirty-seven to forty-three weeks.

If gestation continues longer than these periods, then doctors will prepare you for artificial stimulation of labor, since we are talking about a post-term pregnancy.

This condition is no less dangerous than, because after forty-two weeks the placenta begins to age, which can lead to serious problems with the baby's nutrition and breathing, and other processes are also violated.

There are many reasons for this:

• sometimes hormones are the culprit;
• sometimes - heredity or metabolism;
• slow development of the child is also possible;
• certain diseases of a gynecological or endocrine nature in a woman;
• psychological unpreparedness for childbirth and other factors.

But being under the supervision of a doctor, you will be in control of the situation.

Much more difficult is the situation with premature birth or premature pregnancy. This is how the baby is born before thirty-seven weeks. As a rule, in premature babies, all parameters (height, weight, developmental norms) will be lower than required, so they need either special supervision and care, or emergency medical care, depending on the period.

Preterm birth can occur for various reasons:

• in case of hormonal disorders;
• with injuries, falls, physical damage;
• with emotional stress, severe nervous shock;
• or cervix;
• if the cervix is ​​weak and cannot hold the fetus, etc.

It is not without reason that wise nature determined the specific period necessary for the child to fully grow and develop in the mother's womb, and if the gestation was more or less than expected, then this will create certain risks and become a danger to both the baby and the mother.

What factors can affect the duration of pregnancy?

The duration of bearing a child will be influenced by many different factors and nuances.

• The number of pregnancies.

There is an opinion that the first pregnancy can be the longest, and subsequent ones are shorter than the previous ones. It is also believed that women who give birth to their first child are highly likely. Of course, this is possible with the psychological unpreparedness of the mother herself.

As for the relationship between the number of pregnancies and their duration, doctors refute this opinion, leaving the possibility of earlier second births only if the second pregnancy occurred immediately after the previous one (weather-aged children). After all, when several years pass, your body will again perceive pregnancy as the first.

• The number of fruits.

If you have (twins, triplets), then, as a rule, labor can begin one to two weeks earlier than in the case of a singleton pregnancy.

Most twins are born at the thirty-seventh week or prematurely, and the duration of pregnancies for triplets averages only thirty-four to thirty-five weeks.

• Gender of the child.

Another opinion that claims that the duration of gestation is influenced by who you expect - a boy or a girl. Someone believes that girls like to be late, while others, on the contrary, are sure that boys are in no hurry to be born. However, doctors assure that the sex of the child does not really affect the duration of your pregnancy.

• Complications.

In the presence of certain diseases or pathologies, both premature births and pregnancy prolongation are possible - among them are severe hormonal disruptions, and inflammatory, infectious or other diseases of an acute and chronic nature, and disorders in the main systems (CNS, cardiovascular, endocrine) , and , and , and many others.

• Menstrual cycle.

A kind of reference point for a reference point. As already described, with an average menstrual cycle of twenty-eight days, the duration of pregnancy should be about forty weeks.

And if your cycle is longer, for example, thirty-five days? Then ovulation will occur around the seventeenth to eighteenth day. If the cycle is shorter, then ovulation will be earlier (at twenty days - on the tenth). Therefore, to calculate the expected date of delivery, the doctor will, in the first case, add the difference in days to the reference date, and in the second, subtract it.

• Lifestyle.

Any bad habits (alcohol, smoking, drugs) have a very adverse effect on the intrauterine development of the child and the pregnancy itself. Can cause premature birth and excessive excitement, stress, anxiety, negative emotions. And a too amorphous lifestyle, on the contrary, will cause overwearing.

Malnutrition, deficiency of vitamins and useful elements, lack of physical activity, non-compliance with the regimen and many other factors - all this also has a certain effect on the duration of bearing a baby.

Conclusion

Statistics say that only five percent of women give birth to children on a precisely set date. In all other cases, the actual date of birth does not coincide with the calculated estimated one, that is, the babies themselves decide when it is better for them to be born.

See your doctor regularly, follow all his recommendations so that your pregnancy is an easy and pleasant period of time, and childbirth occurs exactly when you need it.

Getting registered for pregnancy, your time begins to be calculated in trimesters and weeks. How many weeks does a pregnancy last during its normal course, and how is the duration of pregnancy and the birth of a baby determined?

Determining the duration of pregnancy

First, I must say that the period is set from a specific date - the date of the beginning of the last menstruation. This is an obstetric period. How many weeks a woman's pregnancy lasts will be counted from this day. The actual term (from conception) is specified at the first screening (first ultrasound) at 11-12 weeks. On ultrasound, the doctor determines the period based on the development of the fetus. By the way, the set gestational age on the first ultrasound is considered more accurate than on the second ultrasound. All children in the womb then grow differently, just like people in general are different in their complexion, there are large babies, and there are small ones.

The time it takes to get pregnant is:

Obstetric months - there are 10 in total;

Simple (familiar to everyone) calendar months - 9 months;

Weeks - 40, that's how many weeks the pregnancy lasts;

Days - 280 days.

On average, any pregnancy lasts 280 days, which is equal to 40 weeks, but remember, this is just an average number. A full-term baby is considered to be between 266 - 294 days or 38 - 42 weeks. It is difficult to indicate the exact date due to the fact that it is difficult to accurately determine the day of ovulation, the date of fertilization of the egg by the sperm and the readiness of the child to be born. On average, labor activity begins at 38-42 weeks - the child is considered full-term and ready to be born.

Definition of EDD (estimated date of birth)

1. Negele method:

In order to calculate the day when one can presumably expect such important event, use the method of calculation according to the Negele formula. It determines the date of conception. It looks like this: 3 months are subtracted from the first day of the last menstruation and 7 days are added. This will be the PDR.

When calculating, it should be taken into account that ovulation does not necessarily occur in the middle of the cycle. If ovulation occurs on days 18-19, this will indicate that the due date will move towards the plus side by one more week.

2. According to the first signs of stirring:

• date of first movement + 5 months = EDD for primiparous;
• date of first movement + 5.5 months = PDR in multiparous.

This method is extremely unreliable, since all women feel the first movements of their baby at different times. On average, this time is 16-20 weeks. But thin, sensitive mothers can feel the movement as early as the 13th week. A plump women- even after the 20th week.

3. According to ultrasound: there are norms for certain indicators for different periods of pregnancy.

Now we know how many weeks a pregnancy lasts. And yet, according to statistics, 10% of pregnancies last more than 42 weeks, which is considered a post-term pregnancy. Usually these are primiparous mothers, whose age is above or below the average childbearing age, as well as women with 5 or more pregnancies. The reasons for the fact that labor activity did not come in due time can be heredity, one or another pathology of the health of the mother or fetus.

In the event that a pregnant woman is faced with the issue of determining the date of birth of a child, she must take into account that there are two stages of pregnancy - embryonic and obstetric.

The embryonic period starts from the date of conception and lasts 38 weeks. After maturation, the egg has two days to fertilize, and the sperm is active for four days, respectively, conception occurs most likely within four days. The moment of conception of the embryo gives rise to the first week of pregnancy.

But since not every woman can even approximately name the date of conception, it was customary for obstetricians to calculate the gestational age from the start date of the last menstrual period.

This gestation period was named obstetric. It has been known since ancient times, when nothing was known about yet, there were no ultrasound machines and the absence of menstruation was considered the main sign of pregnancy.

Another reason to use the obstetric period in practice was the fact that for each woman the duration of the menstrual cycle can vary from 21 to 35 days. In order not to waste time on the definition in each case, it was customary to conduct calculations starting from the 1st day of the last menstruation. In accordance with this, the obstetric period begins its report already from the moment when conception has not yet occurred, but the egg has successfully matured and left.

If a woman has a regular menstrual cycle of 28 days, then the obstetric period is 14 days longer than the embryonic one, since the days of ovulation fall in the middle of the cycle.

The average woman's pregnancy lasts 40 obstetric weeks. If according to the usual calendar it is about nine months, then according to the medical calendar it is about ten. These are the so-called lunar months, the duration of which is 28 days. Accordingly, if you count in days, the duration of pregnancy will be 280 days.

If in a woman's cycle there are shifts up or down, which is not uncommon, then the duration of pregnancy also increases or decreases. In this case the embryonic period may differ from the obstetric one by more than a month.

To obstetric term determine the due date, it is necessary to add nine months and seven days to the beginning of the last menstruation. But it’s easier to count according to the following formula: subtract three months from the start date of the last cycle and add seven days.

The calculation method described above applies only to those women whose cycle lasts 28 days. If it is shorter or longer, then it is necessary to count as follows: nine months and seven days are added to the first day of the last menstruation, and then those days by which the cycle differs from the 28-day one are subtracted or added.

With the help of ultrasound, it is possible to accurately determine the gestational age if the diagnosis is carried out in the first trimester. If more time has passed, then the constitutional features of the fetus may affect the accuracy of the determination. The term with the help of ultrasound is set according to, which is a rather conditional definition, since the fetus can be both large and small in size and this is due to many factors, including genetics.

Pregnancy is considered normal if obstetric term differs from the term according to ultrasound by no more than two weeks. A significant deviation from the norm indicates a pathology in the development of the fetus.

If we talk about what obstetric term is the norm, then this figure varies from 38 to 42 weeks. Deviations from the norm up or down can have unpleasant consequences.

A baby born before 38 completed weeks is considered premature. And the longer the period of prematurity, the higher the likelihood that the child will be born with serious health problems. Among the most common complications in this case the following may be mentioned: