The duration of pregnancy is significant indicator. It is used to evaluate how the fetus is developing and to find out the expected date of birth. There are many ways in which a pregnant woman can determine her due date (for example, by the date of her last period, by ovulation).

Ultrasound diagnostics (USD) deserves special attention. It is prescribed during the gestation period for several reasons. First of all, ultrasound is necessary to confirm the development of intrauterine pregnancy. Reasons for performing a scan include determining the length of the gestation period.

Features of setting a deadline

By using ultrasound diagnostics the duration of the gestation period can be determined as accurately as possible in the first trimester. In the following trimesters, the information received is not entirely correct. Errors arise due to the constitutional characteristics of fetal development, as well as due to existing and progressive complications in some women during pregnancy.

How is the duration of gestation determined using ultrasound?

In the first 3 months, when it is impossible to see the embryo, specialists will determine the due date using ultrasound by the calculated SVD of the fetal egg - the average internal diameter. This parameter is determined using the algorithm below:

  • the anteroposterior and longitudinal dimensions of the fetal egg are measured during longitudinal scanning;
  • The width is measured during transverse scanning;
  • The arithmetic mean is calculated from the obtained numbers.

At 5.5 weeks. the average internal diameter is characterized by values ​​from 0.6 to 0.7 cm. Every day the embryo grows in a normally developing pregnancy:

  • at 6 weeks the indicator in question already becomes equal to 1.1 cm;
  • at 6.5 weeks - 1.4 cm;
  • at 7 weeks - 1.9 cm;
  • at 7.5 weeks - 2.3 cm;
  • at 8 weeks - 2.7 cm.

When the embryo begins to be visualized, the indicator that allows you to find out the duration of the gestation period becomes CTR - a size called the coccyx-parietal.

Determination of CTE by ultrasound

It is determined by sagittal scanning. This parameter means the maximum distance from the coccyx to the outer contour of the head end:

  • at 1 month and 3 weeks CTE is 0.81 cm;
  • at 2 months - 1.48 cm;
  • at 2 months and 1 week - 2.24 cm;
  • at 2 months and 2 weeks - 3.12 cm;
  • at 2 months and 3 weeks - 4.21 cm;
  • at 3 months - 5.11 cm;
  • at 3 months and 1 week - 6.32 cm;
  • at 3 months and 2 weeks - 7.67 cm.

In the second and next trimesters, the duration of pregnancy is determined by various fetometric indicators.

Specialists may take into account the circumference of the fetal head, biparietal size, average abdominal diameters and chest, abdominal size by circumference, femur by length.

What period does ultrasound show: obstetric or from the moment of conception?

Obstetricians-gynecologists use terms such as obstetric and gestational (embryonic) terms of pregnancy in their work. There is a slight difference between these concepts. By obstetric period we mean the number of weeks that have passed since the beginning of the last menstruation. The gestational (embryonic) period is the period that begins from the moment of fertilization of the egg.

The period determined by ultrasound is considered embryonic. In obstetric practice, the first concept is widely used. That is why, in order to avoid confusion, experts convert the gestational period to the obstetric period, adding 2 weeks to it.

If the period calculated according to ultrasound data exceeds the obstetric...

Theoretically, the gestational age is a couple of weeks less than the obstetric one. However, sometimes ultrasound diagnostics show something completely different. Some women note that their gestational age according to ultrasound is longer than the obstetric one. This is a completely acceptable phenomenon.

The difference is explained by a decrease in the accuracy of determining the date as the fetus develops. The most accurate information is provided by an ultrasound scan performed in the first 3 months of pregnancy. During this period, all women develop the fetus almost equally, so errors in determining the term are minimal.

In the second trimester, the gestational age can be determined quite accurately based on fetometric parameters, but in the third trimester, errors already occur due to the fact that each fetus begins to develop individually and genetic factors influence it. The errors in some cases are ±3-4 weeks. In the last trimester of pregnancy, fetometry is recommended to be used not to clarify the duration of gestation, but to determine whether the size of the fetus corresponds to an already known period.

Why is the deadline specified using ultrasound?

Post-term pregnancy is one of the problems faced by pregnant women. In this condition, the embryonic and obstetric periods are longer than the established values. Normal pregnancy lasts 38 embryonic or 40 obstetric weeks. Post-term pregnancy is considered a factor that increases the likelihood of complications during delivery and leads to increased rates of perinatal morbidity and mortality.

To prevent the consequences of post-term pregnancy, there are certain preventive measures. One of them is the exact determination of the gestational age based on the results of ultrasound diagnostics (it is advisable that pregnant women undergo scanning no later than 20 weeks). Determining the number of weeks also avoids unnecessary stimulation of labor.

Knowing the duration of the gestation period allows the doctor to determine whether the fetus is developing according to the norm and whether there are any deviations. Another reason why you need to know the exact number of weeks is the need for a woman to undergo screenings and take various tests at a certain time (if you take a particular test later or earlier, you can get an unreliable result).

In conclusion, it is worth noting that ultrasound scanning is a fairly simple way to determine the duration of pregnancy. The method provides the most accurate information in the first trimester. It is from the period calculated at the beginning of pregnancy that doctors base the future. It is also worth noting that many mothers are interested in the safety of ultrasound. Ultrasonic waves can cause harm. However, modern devices have minimal impact on the body, so the diagnostic method is considered safe for both the expectant mother and the fetus.

The availability of ultrasound diagnostics allows a woman who has just learned about her pregnancy not to speculate about the due date, but to find out exactly how her baby is developing. Naturally, when visiting an ultrasound room, a woman roughly assumes what time the doctor will name, but it happens that her expectations are not met.

How often does this happen, how can we explain the situation when the term according to ultrasound differs from the period according to menstruation, or the size of the fetus differs from the standard at a specific period?

How much can you trust ultrasound?

Ladies who really want to get pregnant want to know about a miracle happening in their lives as early as possible, literally in the first days of the delay. Of course, you can always buy a pregnancy test. But even ultra-sensitive tests can only accurately give a specific answer to the question “has pregnancy occurred?” They are able to answer yes or no, but more precise methods will be needed to set the deadline.

Positive pregnancy test

During a manual examination of a pregnant woman, an obstetrician-gynecologist may notice that the uterus is loose and slightly enlarged. But this phenomenon is also observed before menstruation. To accurately clarify the situation, you will need an ultrasound examination.

Ultrasound can accurately determine pregnancy when the level of hCG (human chorionic gonadotropin) in a woman’s blood exceeds one thousand units. In this case, the doctor is already able to see the fertilized egg in the uterine cavity (if multiple pregnancy- two or three fertilized eggs). The longer the period, the more complete the picture the study shows - the doctor will note the presence of not only the fertilized egg, but also the yolk sac in it, or even see the embryo and its heartbeat, and will be able to measure the CTE of the embryo (the distance from the tailbone to the crown).

If your menstrual cycle is more than 30 days, the gestational age according to ultrasound and menstruation may differ significantly.

The following situation often arises: a woman comes for an ultrasound, the doctor asks about the date of her last menstruation, conducts a study, and then announces that the pregnancy most likely turned out to be frozen - the embryo and its heartbeat are not visualized, a fertilized egg is visible, the size of which is smaller than it should be be. The doctor may be wrong if a woman had late ovulation. For a significant proportion of women, the menstrual cycle is not the standard 28 days, but 33, or even 35-40. This means that conception did not occur on days 14-16 of the cycle, but a week or two later, and the woman simply came for the ultrasound too early, so the fetus was not seen. Most likely, the pregnancy will not be frozen and the fetus is developing normally, it’s just worth repeating the study in a couple of weeks to make sure there is no mistake. It is also possible to explain the situation when pregnancy is not visible at all on an ultrasound: probably the level of hCG in the blood less than that, in which pregnancy can be seen.

Differences in pregnancy terms according to menstruation and ultrasound

Obstetric gestational age is calculated by week

All obstetricians and gynecologists use the term “obstetric period” when determining the duration of pregnancy. This allows all gynecologists in the world to speak the same language. It is carried out in weeks, counting from the first day of the last menstruation. The first and second obstetric weeks are those weeks during which the egg is still maturing in the body, which will subsequently be released from the ovary during ovulation and meet with the sperm.

Thus, a woman who has a standard menstrual cycle of 28 days and comes to the doctor with a delay of one week will be diagnosed with pregnancy at exactly five obstetric weeks. At the same time, an ultrasound examination can set a slightly shorter period - three or four weeks. How justified is this and why does the deadline not match? This situation is normal, since ultrasound does not aim to determine the exact period in weeks, but to determine how many weeks from conception the fetus is developed according to its parameters (its gestational age). Understanding the difference between these two concepts is important. Therefore, a discrepancy of 1-2 weeks between the period according to menstruation and according to ultrasound in favor of menstruation (i.e. the period according to menstruation is longer, but according to ultrasound is less) is a common occurrence, there is nothing wrong with it.

How to determine the gestational age with an irregular cycle?

Some women suffer from hormonal imbalances and, as a result, irregular cycles. With pathologies such as polycystic disease, multifollicular ovaries, and excessive amounts of male sex hormones, menstruation may not occur for several months. However, ovulation with such disorders still occurs from time to time, which means that such women have almost the same chance of getting pregnant as others.

The girl remembers the date of her last menstruation

If pregnancy is not desirable for you, the use of contraception is mandatory, even if you suffer from irregular cycles and have not had a period for several months.

Often, women with irregular cycles do not consider it necessary to use protection, believing that they will definitely not be able to get pregnant. In this case, you can detect pregnancy in the third or even fourth month, because the absence of menstruation for several months becomes a kind of norm. Correct calculation of the obstetric term in such a situation is practically impossible, therefore, when determining the term, the doctor can rely solely on ultrasound data. If the fetus is not too large or too small, ultrasound can determine the gestational age of the fetus to within 2-3 weeks. The date of birth will also be determined using an unconventional method - by counting 40 weeks from the first day of the last menstruation, and relying on ultrasound data.

In what cases is the term according to ultrasound ahead of the obstetric one?

Currently in Russia, all pregnant women are given the right to undergo free ultrasound examinations three times. They are usually prescribed between 11 and 14 weeks, between 18 and 22, and between 32 and 34. Each of these ultrasounds has its own goals (the first is to determine whether gross malformations of the fetus and genetic abnormalities have been detected, the second is to monitor the development of internal organs, the third is determining the condition of the placenta, the position of the fetus and its approximate weight). However, with each examination, the doctor determines how many weeks the fetus is developed. And often this period is ahead of the obstetric period. For example, a woman knows for sure that her pregnancy is 20 weeks, and the doctor indicated in the conclusion that the size of the fetus corresponds to 22 weeks. Why is this situation happening? There is no error in it. This can be explained as follows:

  • The fruit is large. The large size of the fetus, which is ahead of its gestational age, is not a pathology. Just like all people, the fetus already in the womb has its own individual characteristics.

  • The size of the fruit is slightly smaller than it should be. This may well be a variant of the norm, perhaps the baby is just small, especially if his parents are no different tall and impressive weight.
  • Obstetric weeks are incorrectly defined. There are cases when bleeding, which a woman mistakes for her next period, is actually a threat of miscarriage during a pregnancy that has already occurred in the previous cycle. This phenomenon is popularly called “washing the fetus.” It turns out that the woman tells the doctor one date of her last menstruation, believing that conception occurred in this cycle, whereas in fact it happened in the previous one, and accordingly, the obstetric period will be longer.

How often is ultrasound wrong?

There is always a possibility of error, both up and down, when determining the due date using ultrasound. Why does this happen and how many factors are to blame for this? There are several of them: outdated equipment, insufficient qualifications of a functional diagnostics doctor, confusion with the date of the last menstruation, the fetus was not immediately seen, the individual characteristics of the fetus (too large or too small). You can minimize the risk of an error occurring. It is enough to visit trusted medical centers where the level of qualifications of doctors and the quality of equipment is beyond doubt, and also to carefully monitor your cycle and know exactly the date of your last menstruation.

Many expectant mothers worry that, according to the results of an ultrasound examination, the gestational age suddenly turns out to be two weeks shorter or, conversely, longer than the period. Their worries are understandable. It is necessary to correctly calculate the expected date of birth. Because both late and premature births can significantly affect the health of the child.

However, before you panic, you need to figure out what calculation method the doctor used when conducting ultrasound diagnostics. And most likely it will turn out that everything is fine with the baby. You can just count it differently.

A shorter or longer period is associated with different approach to its definition

How and why are the weeks of the cherished nine months counted?

And yet, why does the study suddenly indicate that the due date is 2 weeks less or more than according to menstruation, and how to correctly calculate the expected date of birth? There are several methods for this in medical practice.

The simplest of them is based on the fact that on average pregnancy lasts no more than 40 weeks or 280 days. This is the so-called “obstetric period”. This is how long it usually takes from the start of your last period to the birth of your baby. The first question that a future mother is asked at the antenatal clinic is: “When was the last time your period started?”

To find out the expected date of birth of the heir, you need to count three months ago from this day, and then add 7 days.

This “obstetric” formula was developed by the French gynecologist F.K. Negele. However, it is only suitable for women with a regular 28-day menstrual cycle. It is imperative to keep in mind that it is impossible to predict the specific date of birth. It is only assumed. This is a period of ± 10-12 days. After all, for each woman everything is strictly individual.

Determination of the embryonic period

Another method is used to calculate “embryonic life.” It is not counted according to menstruation, but from the day of conception, which, as a rule, coincides with ovulation. A woman's egg matures by the beginning of the third week of the menstrual cycle. Modern doctors know that fertilization can occur after ovulation for another two days. The activity of male sperm lasts longer - four days. Thus, conception can occur within about six days. The “embryonic period” thus differs from the “obstetric period”, which is approximately fourteen days longer.


As a rule, in antenatal clinics and during ultrasound diagnostics, more calculations are used based on the “obstetric period”, because it is easier to ask patients when their periods were than to find out exact date conception. Almost everyone finds it difficult to name it.

Other methods of determining the period are also used. For example, by the size of the uterus or by the movement of the fetus. However, these criteria are purely individual in nature for each woman in labor and, because of this, are less accurate. Indeed, with the same time intervals of gestation in different women uterine parameters vary over a very wide range, which makes it impossible to estimate the period with weekly accuracy in each specific case.

Intrauterine movements of the fetus are also felt very subjectively, this is influenced by the sensitivity threshold, which is different for all women. So, for example, one expectant mother begins to feel the baby kicking from the inside from the eighteenth week, and another - only from the twenty-second. And this despite the fact that in reality the activity of the fetus manifests itself already from the second month, unnoticed by the mother.



Is pregnancy due date determined by ultrasound?

Quite often among expectant mothers there is a misconception that ultrasound determines the period of pregnancy and solves this problem exclusively. In fact, this study provides doctors with very different insights. The ultrasound procedure during pregnancy helps to solve a problem that is relevant for monitoring the condition of the unborn baby, namely, with what period of waiting for the baby the information about the size and other characteristics of the fetus is currently comparable.

If the expected period of waiting for a child is 22 weeks, and an ultrasound examination shows parameters characteristic of 19 weeks, then doctors will not think that the date of future birth is determined incorrectly. They will come to the conclusion that the baby is developmentally delayed. This means that other tests are required to fully understand the causes of the problem. Also, setting the correlation with the duration of pregnancy allows you to estimate the growth rate. For the majority, they are normal, which is why the illusion arises that the ultrasound correctly showed how much time has passed since the day of conception.

It is also necessary to take into account the following fact: in the first 3 months, the ratio of the data obtained from an ultrasound examination of the fetus is mainly maintained according to tables that are based on the “embryonic period”. Up to 12 weeks, the CTE of the embryo (coccygeal-parietal size) is assessed, and the SVD indicator (average diameter of the ovum) is also calculated. But later, that is, after three months of waiting for the baby, tables are used that are calculated according to the “obstetric period” data, and not the “embryonic period”, which, as we found out, is almost half a month less.

If the doctor who examined the patient did not initially add these 2 weeks, then later discrepancies appear between the periods according to ultrasound data up to 12 weeks and after. But in reality it turns out that there is no disagreement. You just need to add a couple of weeks to the result obtained during the first ultrasound examinations.



 The purpose of ultrasound is to monitor the progress of pregnancy

Let us add that specific conclusions about the rate of fetal growth and its development can only be made based on combining data, including the date of the last menstruation, the date of conception, and ultrasound results over time.

Pregnancy is one of the most beautiful periods in the life of a representative of the fair sex. It is worth noting that medicine knows two options for calculating the time of gestation in the uterus: the obstetric gestational age and the real one.

Where does it all begin?

To begin with, it is worth talking about how fertilization occurs. Around the middle of the month, the female egg leaves the follicle and slowly moves along. This is where it meets the male cell. The chromosomes then fuse and conception occurs. Having descended into the uterine muscle, the fertilized egg penetrates the endometrium, and from this moment we can assume that the pregnancy has taken place.

Determination of gestational age

When a woman realizes that she is in an interesting position, her initial task is to determine the timing. The gestational age is calculated by week. Typically, the period of time during which the baby is in the mother's womb is 40 weeks. A slight shift in one direction or another is considered normal and does not require any correction. Doctors distinguish between the obstetric gestational age and the real one.

Real gestation time

This period starts from the moment when ovulation occurred. The release of the egg from the follicle is the day from which the actual gestational age is calculated. Most women's clinics that monitor the course of pregnancy use this method of calculation. If you decide to take a blood test to determine the content in it, you will also be provided with a result that indicates the real value of the period.

Obstetric gestational age

This time period begins its countdown from the first day of the last bleeding from the woman’s genital tract. This date is used to calculate the expected date of birth of the baby. Also, many representatives of the fair sex use this method to determine the duration of pregnancy. This is why women so often have discrepancies with the calculation made by the doctor.

Obstetric gestational age and real

In most cases, the difference between these counting methods is two weeks. In a standard female cycle of twenty-eight days, the release of the egg from the ovary occurs exactly two weeks after the start of the last menstruation.

However, not all representatives of the fair sex have a standard cycle length. For example, some women ovulate one week after the start of their last period. In such cases, the difference between the obstetric and actual terms will be one week.

If a woman’s egg was released three weeks after the start of her last menstruation, then in this case the obstetric pregnancy period and the real one will have a difference of twenty-one days.

All situations described are normal. That is why the gestational age by week should be set taking into account the length of the woman’s menstrual cycle. It is impossible to equate all representatives of the fair sex to generally accepted standards. This can lead to incorrect calculation of the baby's gestation period.

pregnancy by ultrasound

There are situations when a woman cannot name the date of the first day of her last menstruation. This situation often occurs if a woman has recently given birth or is breastfeeding. In such cases, representatives of the fair sex are recommended to undergo diagnostics using an ultrasound machine (ultrasound).

A short period of pregnancy, which is not yet possible to determine by manual examination, is easily diagnosed by ultrasound. It is worth noting that a specialist can determine the presence of a woman in the uterus starting from the fourth obstetric week. All measurements and determinations of the period are calculated using the obstetric method.

Instead of a conclusion

If you don't know how to calculate your gestational age, ask your doctor. In most cases, it is enough to know the date of the last menstruation and the length of the female menstrual cycle. If necessary, an ultrasound examination is also prescribed. Carry out the calculation using the same method used by the specialist. Only in this case you will not encounter discrepancies and will not find yourself in a controversial situation.

Gestational age is an important parameter on the basis of which the growth and development of the fetus is analyzed, and the expected date of birth is calculated. The difference in numbers can lead to bewilderment and confusion for both expectant mothers and doctors. The gestational age can be determined by various parameters: the results of an ultrasound examination, the size of the uterus during a vaginal examination, movement, but most often the main reference point is menstruation. What does it mean if these numbers do not coincide, for example, the period according to ultrasound is longer than that according to menstruation? When should an expectant mother worry? Can a doctor make a mistake and how to calculate correctly?

Read in this article

Reasons for differences in obstetric timing and menstruation

For a more thorough understanding, you should understand on the basis of what parameters the gestational age can be determined.

  • The most significant guideline for which you need to know is the first day of the onset of the last bleeding. If a woman remembers this date exactly, then in all situations this parameter is given preference.
  • The gestational age can also be determined by ultrasound examination of the fetus. During the entire period of pregnancy, the woman performs it at least three times. The most informative way to determine the due date is an ultrasound examination at 11–13 weeks. The main parameter measured is CTE (distance from the coccyx to the crown of the embryo). Its value is used to determine the age in weeks. Sometimes ultrasound is performed at a very short stage, when visualization of even the embryo itself is difficult, and only the fertilized egg is determined. It happens that some devices “not designed” for obstetrics can give a date from the moment of ovulation. In this situation, of course, the period according to menstruation and ultrasound does not coincide. The difference will be on average 2 - 3 weeks. As a rule, obstetrician-gynecologists know such nuances of research, and take this into account when determining the number of weeks of pregnancy.
  • An important parameter is determining the degree of uterine enlargement during the initial examination of a woman by a gynecologist. Experienced doctors can tell the period with an accuracy of several days. But with each month of pregnancy, the error in setting the due date increases. The most informative study is from 7 to 16 weeks.
  • Also, the gestational age can be determined by the beginning of fetal movements. On average, a woman feels the onset of movement at 20-22 weeks during her first pregnancy, and at 18-20 weeks during the second pregnancy. But the unborn baby begins to actively move from the second month. Therefore, very often women note that even at 14 - 16 weeks they can distinguish the movement of their baby. That is why this study gives a very approximate and subjective result. In such situations, a discrepancy in gestational age may also occur.

It becomes clear that we have to take into account all the nuances and determine the number of weeks of gestation using all possible methods. In case of significant deviations, the average period is displayed with an emphasis on the indicator for menstruation or ultrasound. Why might there be differences? Let's consider the most popular situations when the numbers will vary.

Short or long menstrual cycle

Conception occurs during ovulation, usually on days 14–16. In women whose cycle length is more or less than the standard 28 days, the release of the egg from the ovary is shifted. Ovulation can occur at the beginning (even on the 3rd - 5th day of the critical days) or on the eve of menstruation. Accordingly, the absence of a pattern leads to the fact that the gestational age in terms of fetal size (this is determined by ultrasound) may not correspond to similar figures for menstruation. But, as a rule, such a gap is no more than 2 - 3 weeks and can be observed throughout the entire pregnancy.

With a short or long cycle, women often take the most early stages. Discharge, of course, differs from regular menstruation in the number of days and abundance, but attention is not always paid to this.

Irregular periods

Often the period according to ultrasound is less than that of menstruation if a woman’s cycle is completely irregular and the interval between critical days is more than 35 days. This happens with PCOS (polycystic ovary syndrome), endocrine diseases, with pathology of the pituitary gland and hypothalamus, etc. If the pregnancy is planned, then the girl can purposefully “catch” ovulation, which is not so easy to do in such a situation. The most convenient way is to build a graph, in addition to which you can determine the release of an egg from the ovary. If the doctor knows the approximate date of ovulation, then it will be easier to compare all the dates and determine the most accurate one.

Cycle failure

Pregnancy is also possible against the background. This could be a one-time failure caused by external factors, and induced, for example, while taking hormonal contraceptives. Girls using emergency contraception, for example, or, believe that unprotected sex immediately after taking the pills will also not lead to pregnancy. In fact, these hormonal drugs only prevent possible conception, which could happen within 48 - 72 hours before taking the drug.

Failure to follow the rules for taking oral contraceptives - skipping a pill, changing the time - can lead to disruption of the menstrual cycle and pregnancy. In such a situation, there is also often a difference in the period according to menstruation, ultrasound and other parameters.

Cycle failure can occur against the background of stress and psycho-emotional experiences, as well as with an increase in body weight. If conception occurs during just such a period, then differences in the established timing may be observed.

Lactation

During breastfeeding, especially during the first year, the release of an egg may not exactly follow the cyclicality of the menstrual cycle. As a result, when calculating the period based on menstruation, a big mistake in terms is made, sometimes up to 3 - 4 weeks.

Intrauterine interventions

Any manipulations accompanied by penetration into the uterine cavity can cause menstrual irregularities. Also, after them, for another month or two, irregular spotting is often observed, which a woman can falsely mistake for menstruation. This can happen after diagnostic curettages, hysteroscopies, abortions (including medical ones), etc.

When using assisted conception techniques

It is often necessary to resort to stimulating ovulation in a woman, creating artificial hormonal levels for conception to occur. In such cases, there may also be a difference between ultrasound and menstruation. Especially if IVF was used ( in vitro fertilization). In such situations, it is difficult for women to figure out the timing on their own, since eggs are first collected and fertilized outside the woman’s body. And only after this, on the 21st day of the cycle, the embryos are transferred. As a rule, the difference in terms of ultrasound and menstruation will be the same in all studies, for example, two or three weeks.

If there was a threat of interruption early

Early pregnancy may be accompanied by various types of spotting, which a woman may mistake for her period. In fact, these are the first symptoms of a threat of interruption. This can continue for up to two to three months, during which bloody spotting or even moderate discharge will appear on the supposed critical days. In such situations, the discrepancy in the period figures between menstruation and data obtained by other methods will be immediately interpreted correctly with a thorough history taking.

Development of a large fetus

In case of development in utero large fruit the false impression is created that the pregnancy is greater by ultrasound than by menstruation. However, such a difference will be visible starting from 20 - 22 weeks. Often only certain parameters of the baby are ahead, for example, abdominal circumference or length of the femur. At 11 - 13 weeks, the gestational age according to ultrasound should correspond to the others.

Allowable difference

Determining the due date is important not only for determining the expected date of birth (EDD), but also for assessing the growth rate of the baby in utero. For example, a developmental delay of more than 4 - 6 weeks is an indication for emergency delivery at any time during pregnancy.

A gap of up to two weeks is acceptable. It is also not critical if the difference can be seen from the very beginning of pregnancy. This indicates that errors were initially made in the definition.

If the period according to ultrasound exceeds the period according to menstruation, this has a more favorable prognosis than the opposite situation. If there is a delay, you should make sure that the fetus is not suffering in utero, that it has enough nutrients and oxygen, and that the placenta is functioning fully.

What is the target date for childbirth?

Both doctors and women often face the question of how to determine PDR - by ultrasound or by menstruation. The approach is individual in each situation.

If expectant mother If she clearly remembers the date of her last menstruation, her cycle is regular and there have been no special changes in her lifestyle recently, then preference is given to menstruation.

In a situation where a woman has difficulty remembering the last critical days, or her cycle is irregular, lasting more than 35 days, then she should be guided by an ultrasound of the fetus. Moreover, all dates of its completion are taken into account, compared, and only after that the expected date of birth is determined.

Why do you count weeks of pregnancy?

Everyone knows that the duration of pregnancy is nine months. However, this is a very average figure. For more careful monitoring of a pregnant woman, monitoring the rate of growth and development of the fetus, periods of weeks and days are used. Thus, pregnancy is considered full-term from 37 to 42 weeks of gestation, which ranges from 259 to 294 days. A child born in this interval has organ systems fully adapted to life in the Earth’s atmosphere (of course, if the baby does not have a congenital pathology or infection).

This is why you need to know the exact date of pregnancy:

  • Identify pathologies in the baby’s maturation rate in a timely manner and carry out the necessary treatment. Sometimes this is even premature delivery, when the continued presence of the baby in utero has a high risk for his life.
  • Systematize the clinical examination of pregnant women and the timing of registration. Based on the results, they are assessed possible complications, measures are being taken to prevent them.
  • Knowing the gestational age, you can set the deadline for the expected date of birth. Postmaturity can negatively affect the baby's health, in which case labor may be induced.

Is the date determined by ultrasound accurate?

During pregnancy, ultrasound is performed several times. Which time frame is more accurate? First of all, you should take into account the results of ultrasound obtained from 11 to 13 weeks inclusive. It is during this period that the size of the baby is such that it is possible to accurately determine the landmarks for measurement (as a rule, this is CTE - the distance from the coccyx to the top of the parietal bone on the head of the embryo), which can be displayed on the screen at the same time.

In the short term, the parameters are approximate, since often only the fertilized egg is visible or the structures of the unborn baby are not clearly distinguishable.

After 16 - 18 weeks, only individual parts of the fetus can be displayed on the monitor screen - the head, arm, leg or tummy. These structures are measured and the approximate gestational age is determined using summary tables. The longer the period, the less indicative the numbers, since in the mother’s belly some are skinny, while others have chubby cheeks and legs.

Determining the gestational age has important diagnostic and prognostic significance for successful management women while carrying a child and preparing her for childbirth. That is why every girl should strictly lead menstrual calendar and mark all events significant for health in it. This great help doctors, help in solving emerging problems. Of course, it doesn’t matter whether they gave birth by ultrasound or by menstruation, the main thing is that mother and baby are healthy and their lives are not in danger. And this can only be achieved through coordinated work between doctors and women.