Why is ultrasound pregnancy shorter? Why is the gestational age according to ultrasound different from obstetric? Why is the term specified using ultrasound?

A woman who finds herself in a position in most cases is interested in the question of which of the two is true: the period according to menstruation or the period according to ultrasound. And if experienced representatives of the fair sex do not have problems determining the age of the fetus, then pregnant women for the first time do not have a clear idea of the differences between obstetric and gestational periods.

When diagnosing pregnancy, the gynecologist announces the obstetric period in weeks. An important feature is that the reporting point is the first day of the menstrual cycle. As you know, conception occurs during the period of ovulation (approximately day 14). In this situation, in fact, the woman is not yet pregnant at the moment when menstruation begins. That is why, in most cases, the approximate date of birth (APD) differs by 2 weeks from the real one or less than the one set by ultrasound.

But it is precisely this method that is optimal and is used in obstetric practice. This is fair, because the egg begins its development on the first day of menstruation, and then matures and is fertilized, and if not, it dies. Therefore, the obstetric period can be considered the “age” of the egg. Also, menstrual cycles are individual and can vary greatly from woman to woman. Although the 28-day menstrual cycle is generally accepted as a reference, actual values can vary greatly.

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So, many women may have a cycle longer than 28 days, for example, 35. In this case, ovulation occurs on the 16-17th day. Accordingly, if the cycle is shorter, for example, 21 days, then the release of the egg from the ovarian body occurs on the 10-11th day. To simplify the work of specialists, it is customary to consider the beginning of pregnancy from the first day of the last menstruation, which is called the obstetric period.

According to the results of ultrasound examination

In the case of determining fetal maturity based on the results of an ultrasound examination, a controversial situation may arise:

The temporal course of pregnancy by ultrasound is determined by assessing fetal development, metric indicators, the condition of the uterus and the placental barrier (in the 2nd and 3rd trimesters). One of the indicators is CTR (coccygeal-parietal size), which is almost the same in different fetuses at the initial stages of development. Pay attention to the size of the fertilized egg in the first 12 weeks of gestation. The most accurate number of weeks is determined using ultrasound in the first trimester of pregnancy (up to 12 weeks). Afterwards, the indicators may vary up or down due to the individual developmental characteristics of the unborn child.
As a rule, the embryonic period established by ultrasound indicates the period from the moment of fertilization of the egg with male material to the present, therefore it is considered factually correct. Most often, there are discrepancies of approximately 2 weeks between the PDR according to ultrasound or calculated by monthly. But certificates of incapacity for work and other documents are issued based on the obstetric age of the fetus, which is indicated in the mother’s passport and documentation in the antenatal clinic.

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Conclusion and conclusions

Be that as it may, it is almost impossible to establish exactly when the child was conceived and when he will be born. Even knowing the exact date of the “decisive” sexual intercourse, one cannot be sure that fertilization took place on that very day, since sperm can exist for 24 hours. Moreover, there are many factors that provoke labor earlier than expected.

If we consider the question of the correctness of the period based on menstruation or ultrasound, it should be said that both are correct, but traditionally obstetricians focus on the first option. This allows you to avoid confusion in the future and consider possible delivery on the specified dates. But, according to statistics, not every woman gives birth on the day established by specialists. It is generally accepted that a 4-week gap is normal (from 38 to 42 weeks of gestation, respectively).

The duration of pregnancy is a 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 duration of the gestation period.

Features of setting a deadline

With the help of 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 can take into account the size of the fetal head in circumference, biparietal size, the average diameters of the abdomen and chest, the size of the abdomen in circumference, and the length of the femur.

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 gestational age. 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.

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 a 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 they had their periods than to find out the exact date of 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 waiting period 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 mostly kept 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.

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 match, 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 measured parameter is CTE (the 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, obstetricians-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 enlargement of the uterus 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 difference is no more than 2 - 3 weeks and can be observed throughout the entire pregnancy.

With a short or long cycle, women often take menstruation at the earliest 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 can be either a one-time failure caused by external factors, or 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 medications only prevent possible conception that could have occurred within 48 to 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 an artificial hormonal background in order for conception to occur. In such cases, there may also be a difference between ultrasound and menstruation. Especially if IVF (in vitro fertilization) was used. 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 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 the case of the development of a large fetus in utero, a false impression is created that the pregnancy is larger 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 (DOD), but also for assessing the growth rate of the baby in utero. For example, a developmental delay of more than 4 to 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 the expectant mother 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 that are 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, possible complications are assessed and measures are 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 simultaneously.

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 the successful management of a woman during pregnancy and preparing her for childbirth. That is why every girl should strictly maintain a menstrual calendar and mark all events significant for health in it. This is a great help to doctors, a 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.

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 particular calculation method. 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 bloody discharge 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.