The most accurate gestational age. How to determine the gestational age: the most accurate methods. Method for determining the date of ovulation

Pregnancy is a very dynamic process during which the growth and development of the fetus occurs, and restructuring occurs in the woman’s body in accordance with the stage of its development. Therefore, correct determination of the gestational age is very important for understanding the changes that occur in each period gestation(pregnancy).

Information To correctly determine the duration of pregnancy, information about the first day is important last menstrual period, from which it is calculated. This approach is valid for a regular menstrual cycle.

Fertilization usually occurs after ovulation(the release of the egg from the ovary, that is, in the middle of the cycle), therefore this definition of the period is somewhat averaged and differs from the true one by an average of 14-16 days. But since in most cases the exact date of ovulation is unknown (with the exception of in vitro fertilization programs), counting from the first day of the last menstrual period is most often used.

By date of first movement

You can also take into account the date of the first fetal movement. For primiparous women this is usually about 20 weeks, for multiparous women - . But fetal movements are a rather subjective sign (especially in the early stages it can be confused with intestinal function), so it can only be used as an additional one.

Besides data medical history(a set of information obtained by interviewing the patient) when establishing the gestational age, one should focus on objective data obtained during examination, that is, the size of the uterus and the position of its fundus, as well as the results obtained during an ultrasound examination.

Determination of the period based on the height of the uterine fundus

The size of the uterus and the height of its fundus in different terms pregnancy

From the very beginning of pregnancy, the uterus begins to gradually grow and by each month it should have a certain size during the normal development of pregnancy:

• By the end of pregnancy, the uterus reaches the size of a chicken egg;
• The size of the uterus corresponds to the size of a goose egg, which is clearly determined by vaginal examination;
• The uterus is determined at the level of the border of the upper edge of the pubic arch;

• The fundus of the uterus is located in the middle of the distance between the navel and the pubis (4 transverse fingers above the pubic symphysis - the articulation of the pubic bones);
• By pregnancy, the fundus of the uterus is set 2 transverse fingers below the navel;
• The fundus of the uterus is at the level of the navel;
• The bottom of the uterus is determined 2-3 transverse fingers above the navel;
• The fundus of the uterus is installed in the middle of the distance between the navel and the xiphoid process of the sternum;
• This level reaches the xiphoid process and costal arches;
• The fundus of the uterus lowers somewhat due to the expansion of the lower segment (the body is preparing for childbirth) and the lowering of the presenting part (usually the head) and is located in the middle of the distance between the navel and the xiphoid process.

This parameter should be assessed only in conjunction with the others, since the height of the uterine fundus increases in the presence of large fruit, multiple pregnancy, with incorrect position of the fetus, and decreases with a small fetus, with a low standing of the presenting part of the fetus (if there is a threat of abortion). Also, the increased size of the uterus can, especially in the early stages, imitate the presence of myomatous nodes, hydatidiform mole and other pathology.

How to calculate gestational age using ultrasound

Ultrasound examination () is of great help in determining the duration of pregnancy. In the early stages, when the embryo has not yet been identified, the term is set based on the size ovum.

Indicators of the average internal diameter of the ovum

From the moment when the embryo begins to be determined in the fertilized egg, the gestational age is determined based on the size coccygeal-parietal size of the embryo/fetus(this is the maximum distance from the head end of the fetus to its tailbone). This method is more accurate than determining the period by the diameter of the fertilized egg.

Estimation of gestational age based on embryo/fetus

In the second half of pregnancy, the gestational age is determined based on several measurements:

• Biparietal size of the fetal head;
• Fetal abdominal circumference;
• Length of the femur.

The period established on the basis of ultrasound examination is correlated with the menstrual period and the data of objective research.

Duration of pregnancy and determination of the date of birth

The average length of pregnancy is 280 days, which corresponds to 40 weeks. Define the exact date childbirth is impossible for any given pregnancy. Therefore, a term birth (that is, a full-term birth) is considered to be a birth between 37 and 42 weeks of pregnancy. Moreover, at 37 weeks the baby may not yet be ready for extrauterine life, but the birth will not be considered premature. And at 41-42 weeks the baby may be born with signs of postmaturity.

How to calculate your due date

The estimated due date can be determined in the following ways:

• On the first day of the last menstruation: add 280 days to it and get the due date corresponding to 40 weeks of pregnancy. It’s easier to subtract 3 months from the first day of the last menstruation and add 7 days (For example, the first day was March 15, subtract 3 months - December 15 and add 7 days, we get the expected date of birth - December 22);
• By ovulation: from the first day of expected but not occurring menstruation, subtract 14 days and add 273 days. This method is valid for regular menstruation;
• By exact date of fertilization(more often used for in vitro fertilization - 3 months are subtracted from the date or 273 days are added);
• According to the gestational age established at the first visit to the antenatal clinic(more precisely when registering up to 12 weeks);
• By date of first movement: for primiparous women, 20 weeks are added to the date of the first movement, for multiparous women – 22;
• By date of prenatal leave(from 30 weeks to given number add 10 weeks);
• According to ultrasound data(the most accurate for determining the period is the first screening ultrasound at 10-14 weeks, since the fetus does not have characteristics related to race, gender, etc.);
• According to the degree of maturity of the cervix: This method is based on studying the cervix during vaginal examination. In this case, you can determine whether the cervix is ​​mature or not (that is, determine its readiness for childbirth), but not indicate the exact date.
• According to colpocytological test. This method is based on taking material from the cervix and examining it under a microscope to determine the ratio of different cells. Changes in the composition of cells can be used to judge the expected date of birth.

Today, there are many special obstetric calendars that, based on the first day of the last menstruation, make it possible to determine the duration of pregnancy, as well as the expected date of birth.

One day, that very special day comes for every expectant mother. She learns about her new condition. And soon a woman will often hear the question: “What is your (you) deadline?” How to calculate the gestational age in order to answer correctly?

It's pretty simple!

Almost always, the answer to the question about the gestational age will be based on the two most well-known and popular calculation methods - obstetric and embryonic (from conception) terms

Obstetric term

The beginning of pregnancy is the first day of the last menstruation. This method is called obstetric. It does not take into account the individual characteristics of a woman’s body, but is almost universal. Any doctor will use it.

The obstetric method has its own logic. The time limit is calculated from the most early stage pregnancy - the beginning of egg maturation.

Using the obstetric method, the doctor will determine the expected date of birth (ED), as well as the period of maternity leave. In medicine, it is generally accepted that pregnancy lasts 280 days. This is the well-known 40 weeks or 10 lunar months.

Why 10 months and not 9? And why are the months lunar? Astronomy is to blame for this. The moon repeats its phases every 28 days (4 weeks). This is the lunar month. And if you count in calendar months, then only 9 of them really fit into a normal pregnancy.

Embryonic (true) period - from conception

The beginning of pregnancy is the first day of the last menstrual period plus 2 weeks. It is believed that ovulation occurs in the middle of the cycle. In this case, the average period from one period to another is taken - 28 days.

This method of calculating the period is called embryonic or true. But it’s worth wondering: isn’t the truth hiding somewhere else? From a medical point of view, ovulation can occur within 12-18 days from the start of the cycle.

Example. Oksana's husband constantly went on business trips from early spring to late autumn. Sometimes he was home only one or two days a month. Soon after her husband’s next visit, Oksana realized that she was pregnant. And with a smile I thought that I knew the exact date of conception - June 2. After all, before and after that day, she and her husband did not see each other for almost two weeks. Oksana had her last period on May 18-21. And if we consider May 22 as the beginning of the cycle, then conception took place on the twelfth day. And the egg was already mature. Or not?

Another important question here is how long does ovulation last? If strictly according to science, then a few seconds. After all, ovulation is only the release of a mature egg from the follicle. But most of us consider ovulation and the next few (or even many) hours that the egg will live in female body. How many? Sometimes up to two days. By the way, sperm will live approximately the same amount of time in a woman’s body after sexual intercourse. And sometimes longer - up to a week.

So the true day of conception is a real mystery! After all, there may well be two various situations. The egg moves to the uterus for the second day and, literally at the end of its life, is fertilized. Or vice versa. Sperm entered the woman’s body before ovulation and actually “waited” for the release of the egg.

Couples who carefully planned their pregnancy know the day of conception as accurately as possible. In this case, the day of ovulation is determined using a special test (sold in a pharmacy) or ultrasound.

There is another old method for determining ovulation. This is a basal temperature measurement. It is carried out in the morning, at the same time, before getting out of bed (it is recommended not to even open your eyes). The thermometer is placed in the mouth, vagina or rectum. Before ovulation basal temperature decreases slightly and then increases. This means the release of a mature egg.

And sometimes women themselves feel that ovulation has occurred. The lower abdomen ache, the vaginal discharge becomes a little more viscous. And the attraction to the man you love becomes stronger.

That is why many expectant mothers consider their pregnancy period to be the embryonic method: the beginning of the cycle plus 2 weeks or the day of ovulation known to them. In this case, we are talking about the period from conception.

Could there be difficulties?

Lyudmila’s periods often came literally “every once in a while.” The doctor's verdict is ovarian dysfunction. While Luda was not sexually active, she was not too worried. But after marriage, the same question often came. Is delay a manifestation of dysfunction? Or did the contraception not work? One day the second option turned out to be correct. But count the deadline the usual method the doctors could not - there was a clear discrepancy.

Former athlete Valeria had her first period only at the age of 16. And the cycle was not established in any way. Up to six months could pass between critical days. The girl did not go to the doctor. I somehow couldn’t find the time – either studying or personal life. One day, skinny Valeria noticed that she had clearly gained weight. The first reaction is the desire to sit on strict diet and remember your previous sports activities. It’s good that the girl first consulted with her mother. More precisely, with the future grandmother of his child.

Lena's first child just turned ten months old. The baby grew up healthy, and the nursing mother decided to eat melon on the occasion of such a big anniversary. A few hours later she felt sick. Lena thought she was poisoned. But soon the doctors clarified the situation: Lena was pregnant again. The first menstruation after childbirth simply did not have time to begin.

How many more similar cases! If a woman’s periods are irregular or have not arrived at all, as in Lena’s situation, traditional calculations will not help. It's good that there are alternative methods.

How else to determine the deadline?

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• based on a gynecological examination;
• using ultrasound;
• by the first movement of the fetus;
• according to the size of the uterus.

In some cases, the doctor “looks after” all the signs in order to make fewer mistakes in calculating the duration.

Gynecological examination

An experienced gynecologist will be able to calculate the correct period based only on the size of the uterus. The doctor’s hands will accurately determine the boundaries of the uterine cavity. If the uterus is comparable in size to a chicken egg, the period is 4 weeks. And if it’s closer to a goose, then we’re talking about eight weeks.

This method works effectively if the pregnancy is less than 12 weeks.

Ultrasound

Ultrasound scanning these days allows you to effectively examine the fetus and even take some measurements. In the first trimester, the doctor will determine the size of the fertilized egg and compare it with traditional data. In the second and third, the doctor will measure the circumference of the chest, tummy or head. The last “measure” is considered the most accurate for determining the period.

In the first weeks of pregnancy, calculating the due date in this way gives a very exact result. Later, future babies begin to differ greatly: some are larger, some are smaller. Just like in the life that awaits them in the future.

The baby is pushing!

The first movement of the fetus is another indicator. If a woman is preparing to give birth to her first child, she will feel his movements at 20 weeks. If the baby is the second, third, and so on, then the first movement is expected at 18 weeks. This is official medical data. And future kids do not at all think that they must follow them!

The fetus actually makes its first movements in the first trimester of pregnancy. But unborn child still so tiny that mom doesn’t feel anything for many weeks. But there are also exceptions.

Inna was expecting her second child. I was already skinny, but in the first weeks I still lost weight. With a height of 167 cm - 46 kg. And this is in the second trimester! The doctor shook her head disapprovingly and was worried. And Inna felt great. There was almost no nausea, and vomiting occurred occasionally. True, I always wanted oranges, and one red “handsome” one was always in my bag. And there were no problems at all.

The baby pushed at the seventeenth week. First once, and after a couple of hours - again. And the next day, and the day after, the woman experienced the same sensations. At the next appointment with the gynecologist, Inna named the date. The doctor shook her head once again, smiled and clarified - maybe it was gases? Inna laughed - she perfectly remembered the baby’s movements from her first pregnancy and definitely could not have been mistaken.

True, sometimes you can still get confused. If future mom She regularly suffers from flatulence, and is also expecting a baby for the first time; she sometimes mistakes the movement of gas through the intestines for the baby’s movements.

When weeks are equal to centimeters

And one more way, which is related to the size of the uterus. More precisely, with its height. This method is available only to doctors. A pregnant woman lies down on the couch. The doctor takes a measuring tape or special tool– tazomer. Determines the upper and lower boundaries of the uterine cavity and takes measurements.

The height of the uterus in centimeters is the gestational age. That is, if the doctor measures 30 cm, then the gestational age is 30 weeks.

These four methods (usually in combination with each other) provide the most accurate determination of gestational age.

When will he be born?

The expected date of birth will tell the mother when the baby will be born. But this is a theory. Children very rarely follow doctors’ calculations. True, there are exceptions here too.

At an ultrasound at 12 weeks, Lika was diagnosed with PDR - March 10th. Lika just shrugged her shoulders slightly. She carried her first baby for exactly a week. Doctors then said that the baby probably wants to grow up. Indeed, even post-term, my son weighed only 2 kg 700 g at birth.

Therefore, early in the morning of March 10, Lika did not even immediately realize that contractions had begun, and stubbornly tried to get a little more sleep. But it didn't work out. It soon became clear that it had begun. That’s how my daughter was born – right on time.

Naegele's formula:

Quite accurately, the expectant mother can calculate the MPD herself. Of course, if your periods were regular before conception.

1. You need to add seven more days to the first day of your last menstruation, and then subtract three months.
2. Or add 9 months and 7 days to the first day of the last menstruation.

Here is the approximate date of birth of the future baby!

You can find out your PPD using a special pregnancy calendar based on your last menstrual period. In the red line we look for the date of the beginning of the last menstruation, next to it, in the yellow line, we see the date of the probable day of birth.

For example, your last period began on January 28th. Plus seven days is February 4th. Minus three months - we get November 4th. Life will tell how it will actually be.

The main thing is that at any stage the pregnancy should be easy.

Note to moms!

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Gestational age- one of the main components that a gynecologist needs to know about for proper management of pregnancy. After all, on the basis of this, the doctor will prescribe the necessary examinations, tests, routine ultrasounds, monitor intrauterine growth and development of the fetus, and identify possible violations during the pregnancy. In addition, determining the due date allows you to fairly accurately calculate the date of birth and the date of maternity leave. It is necessary for the woman herself to know the duration of her pregnancy in order to mentally prepare for childbirth, have time to prepare a room or corner for the unborn baby, and purchase all the necessary accessories and clothes for him.

In this article we will look at how to determine the duration of pregnancy.

Calculate by monthly

For a woman who comes to register at the antenatal clinic, the gynecologist first of all asks a question about when her last period began. It is from this date that he begins to keep a record, despite the fact that fertilization has not yet occurred. It is known that fertilization of the egg occurs on the day of ovulation, which occurs in the middle of the menstrual cycle. This method of determining the gestational age is called “obstetric”.

An online calculator will help determine the period:

How to determine the gestational age by the date of conception

It is known that conception occurs only during ovulation within 24 hours after the egg leaves the follicle. And the viability of sperm in the female genital tract is up to 3 days. It turns out that the date of sexual intercourse does not always coincide with the date of conception.

Ovulation occurs in the middle of the menstrual cycle. Woman taking care of her menstrual cycle, can quite accurately calculate the onset of ovulation. In addition, many people at this time have characteristic features: aching pain in the lower abdomen, breast swelling, irritability, copious discharge from the vagina, increased sexual desire.

It is worth noting that only those women who have a regular menstrual cycle can determine the gestational age by the date of conception.

Online calculator:

(calculation will take a few seconds)

How to calculate using ultrasound

It is possible to find out the gestational age using the results of an ultrasound examination (ultrasound). It is determined according to the size of the fetus. The first ultrasound of the expectant mother is performed at 12-14 weeks, but it is still impossible to determine the exact date, since the development of the fetus occurs individually in each woman. It is possible to find out the age of the fetus by ultrasound with an accuracy of one day only in the first weeks after conception.

Determination during examination by a gynecologist

A gynecologist can determine a woman's gestational age by the size of her uterus during a gynecological examination. At 5-6 weeks, the size of the uterus can be compared to chicken egg, at 8 weeks - with a goose egg. Later, it will be more difficult to determine how many weeks a woman has based on the size of her uterus.

Find out the due date by the first fetal movement

In the first pregnancy, a woman begins to feel fetal movements at 20 weeks, in the second - at 18 weeks. But this method does not always allow one to determine the period, since some expectant mothers may feel the first movements of the fetus earlier or later than the indicated weeks - some, due to the structural features of the body, cannot feel the movements of the fetus, others confuse the work of the intestines ( increased gas formation) with movements.

Determine by hCG

Human chorionic gonadotropin (hCG)- one of the most important indicators indicating the onset of pregnancy and its normal development. The hormone begins to be produced in the female body after implantation of the embryo into the wall of the uterus. The level of hCG in the blood allows you to find out the approximate age of the fetus. With multiple pregnancy, the level of the hormone in the blood increases in proportion to the number of fetuses.

Having learned about pregnancy, any woman will want to calculate its approximate duration in order to schedule a visit to the doctor, registration with antenatal clinic and, of course, start preparing for significant event in my life - childbirth.

It is not difficult to calculate it, you just need to understand how to do it. It’s easy to find out if you remember the start date of the last cycle, that is, the last menstruation, and count the weeks from it. This period is called obstetric. On the Internet you can now even find special services that calculate the duration of pregnancy in accordance with the start date of the last cycle and its average duration.

But if the cycle is unstable and changes frequently, such a method can hardly be called reliable, so a logical question arises about how to find out exact date pregnancy.

You can find out the period quite accurately by using the new generation, which will especially help in the early stages, at the very beginning of pregnancy. Such tests determine the concentration of beta-hCG, a hormone that begins to be produced, and give an approximate result.

An obstetrician-gynecologist can also tell you how to find out the duration of your pregnancy. As a rule, doctors use two methods: a blood test for a special indicator, beta-hCG, and ultrasound.

A blood test, especially if done closer to 10-12 weeks, may not give an accurate enough result, since at these times the normal limits are already too wide to accurately determine the period. But ultrasound can give results more accurately even obstetric period. Measuring the size of the fetus and comparing them with a table of norms helps to establish the period very accurately, however, it is called embryonic and is often slightly behind the obstetric one. At the same time, the doctor can tell you how to find out the due date; it is not difficult to calculate it.

There are several other ways to find out your gestational age. For example, you can learn how to measure by asking your doctor to show you how to do it. It will be difficult at first, but as the uterus rises, it will become easier to take measurements. Normally, this value is equal to a week of pregnancy.

There is a method that even doctors focus on - the time when the expectant mother begins to feel the fetus moving. This usually happens in Some pregnant women even believe in the superstition that by counting exactly 20 weeks from the moment of the first movements, you can find out the date of birth.

The closer the end of pregnancy is, the easier it is to determine its exact duration using ultrasound. While in the early stages it could interfere or not be enough good equipment, then now that the baby is already big, it’s easier to measure him.

You can ask different doctors how to find out the gestational age, but only the woman herself can accurately answer this question, focusing on her own feelings and well-being.

It should be remembered that in most cases, babies are not born exactly on time, but earlier or later by several days, or even two weeks. This is considered normal, so there is no need to worry. But you should definitely take into account that the due date given by the doctor is only an approximate date, so it is better to prepare for childbirth in advance.

Pregnancy is a long-awaited moment in a woman’s life. From the moment of conception, the expectant mother already wants to know the date of birth of her baby.

Here, everything is not always clear and unambiguous. For example, here is one of the questions I receive daily:

“Please tell me, I’m pregnant, according to my period I should give birth on September 24, according to an ultrasound at 18 weeks the due date is set for October 16, the second ultrasound at 33 weeks is set for October 11. But when I filled out the documents for the maternity hospital, I was sent for another ultrasound, and it showed September 30th. How can this be and what should I do better, save now or wait until it catches on? Thanks in advance".

How to accurately determine the gestational age?

Different methods are used to determine the gestational age and due date.

Determining the gestational age and date of birth based on the date of the last menstruation

Usually the first thing the gynecologist asks at an appointment is the last date.

In obstetrics and gynecology, the cyclicity and regularity of menstruation is an indicator of a woman’s health.

In order to track the regularity of menstruation, a woman needs to keep track of her .

The most common way to determine the date of birth is the method based on the date of the last menstruation.

The starting point is taken first day last menstruation. From this day, 40 weeks or 280 days or 9 calendar months or 10 lunar months are counted - this will be the approximate date of birth.

The date of birth is still being determined using this method. according to Naegele's formula: from the first day of the last menstruation you need to count 3 months ago and add 7 days to this date. This will be the date of expected birth.

For example, the first day of menstruation was October 1st. From this date we count back 3 months (September 1, August 1, July 1 and add 7). It turns out July 8 is the expected date of birth.

ATTENTION! This is only the estimated date of birth, because... many women give birth somewhat earlier or later than this date.

What does this depend on? From many factors. From the course of pregnancy itself, from the maturity of the child, from the readiness of the mother’s body for childbirth, from diseases aggravating pregnancy.

Determining due date by ovulation date

Determining the gestational age and date of birth by ovulation is more accurate. Count the past weeks from the date of ovulation - this will be the gestational age based on the date of ovulation.

If you know the day of your ovulation, then add 273-274 days to this date and get the estimated date of birth.

Determining due date by date of conception

This is a more accurate way if you know for sure date of conception or sexual intercourse, especially if it was the only one. From the moment of conception to the moment of birth, 266 days must pass.

Add 266 to the date of conception and you will get the estimated due date. It will also be approximate, because... exactly day of conception difficult to find out.

What other ways are there to determine the duration of pregnancy?

Determination of gestational age by ultrasound

From the moment the fertilized egg is immersed in the uterine cavity, signs of pregnancy can already be seen using an ultrasound machine. They are determined by the size of the uterus, the size of the fertilized egg, and the size of the embryo. For more later- by the length of the thigh, the length of the shoulder, the size of the child’s head and abdomen, and the thickness of the placenta.

There are special tables from which the doctor calculates the timing of pregnancy by comparing the data obtained.

Determination of gestational age by uterine fundal height (UFH)

At later stages, starting from 14-16 weeks, the uterus emerges from the small pelvis and can already be felt above the woman’s womb. The doctor measures the height of the uterine fundus with a centimeter tape.

As a rule, GMT in centimeters = gestational age in weeks. For example, GMR = 16 cm, which means that according to GMR, a woman is 16 weeks pregnant.

Determining the gestational age by gynecological examination

An examination by a gynecologist is one of the accurate methods for determining the duration of pregnancy. Normally, the uterus measures 3x4x5 cm. During pregnancy, the uterus increases in size, becomes rounded, soft, and its anteroposterior size increases.

When setting the gestational age, the gynecologist focuses on the size of the uterus. They are measured in weeks of pregnancy. For example, uterus the size of a newborn's head– this is 12-13 weeks of pregnancy.

Determining the due date by the first movement

A primiparous woman begins to feel the baby's movements from the 20th week of pregnancy, and multiparous women - from the 18th week.

The doctor will ask you to remember the date of your first movement. From this date, 20 weeks are counted for primiparous women and 22 weeks for multiparous women and the approximate date of birth is obtained.

Sometimes women begin to feel movement with more early dates. For example, from 15 weeks. But in this case, the calculation of the due date will be very inaccurate.

In practice, to determine the gestational age and due date, the doctor will use ALL of these methods.

If there is a discrepancy between the size of the child and the gestational age, this means signs of intrauterine growth retardation and requires special treatment.

Thus, in order to establish the correct gestational age and determine the date of birth, many calculations, measurements, and calculations are required.

Currently, the date of birth is very often determined by doctors or pregnant women themselves, when they decide that the pregnancy should be ended with surgery. C-section, but more on that next time.

Your doctor Semenova Olga

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