How does a doctor determine the period? Pregnancy dates: obstetric and embryonic - how to determine and not get confused about the dates. Determination of gestational age using hCG

02.08.2023 -

Pregnancy calculators

The calculator calculates the duration of your pregnancy based on your last menstrual period. The gestational age is obtained in “obstetric” weeks.

Calculate gestational age

Enter the first day of your last menstrual period

As a rule, every pregnant woman has her own calendar, where she enters all the necessary data, circles important dates, and makes notes. It is usually used to calculate the gestational age.

Considering the nine-month duration of this period, calculations on paper seem to be a very routine task. But modern women live in excellent times - they are not at all obliged to keep such a calendar and do tedious arithmetic, unless, of course, they are so sentimental that they decided to keep their weekly notes as a memory of the wonderful time of pregnancy. You can safely entrust the worries about calculating your pregnancy period to the program. After all, for those who prefer to spend their free hours on activities that are much more useful for the future baby and his mother, there are numerous virtual services like this (we hint at our calculator).

What is needed to calculate the gestational age?

In order to calculate the gestational age right now, you only need to remember the date when your last period began and enter it in the appropriate fields of the form. This number is the starting point of your pregnancy. We are talking about the so-called “obstetric weeks” - all over the world it is customary to count pregnancy this way, although fertilization occurs only in the middle of the cycle. This measure is necessary for the convenience of doctors, but often causes surprise and misunderstanding among patients.

It is worth noting that during an ultrasound examination of the fetus, you will be faced with the fact that the gestational age known to you can be calculated differently - based on the weeks of the fetus’s life, that is, from the day of conception. You may even find a note on the ultrasound examination results sheet that will indicate both dates. In order not to be embarrassed by such contradictions, feel free to ask your doctors what exact stage of pregnancy you are talking about, real or obstetric?

It is very important to emphasize that even if you know exactly the date of conception of the baby, in order to calculate the gestational age using a calculator, you need to use the date of the start of the last menstruation. If you find it difficult to remember, count back 2 weeks - with a standard 28-day cycle, ovulation most often occurs on the 14th day.

I don't remember when I had my period. What to do?

Sometimes it happens that a woman does not know when she had her last period, for example, she does not remember, does not monitor the regularity of her cycle, or has just stopped taking birth control medications. If you have no idea what your gestational age is, they can calculate it using. The most reliable data is obtained in the early stages (up to 12 weeks), when the rate of development of the fertilized egg is still very high and changes are noticeable literally every day. The size of the fertilized egg alone, without taking into account the proportions of the fetus, will tell the doctor a lot. At later dates, errors of up to 2 weeks are possible.

Another very informative method that allows you to calculate the gestational age is biochemical - testing a woman’s blood for the content of hCG - human chorionic gonadotropin. This hormone is produced by the fertilized egg and is present in the body only during pregnancy (by the way, the well-known instant pregnancy test is based on its determination in urine). Even during a healthy pregnancy, the content clearly correlates with the timing. It is worth noting that this is far from a routine method, which requires a lot of time and money, and is used mainly for medical reasons.

It should be mentioned that finding out the gestational age, calculating and guessing the probable age of the fetus is within the competence of the obstetrician when conducting a vaginal examination in the early stages. The main object of study in this case will be the uterus and palpation (manual) determination of its size. Of course, we are not talking about absolute accuracy, but the data obtained is quite sufficient for successful monitoring of the health of the expectant mother and fetus.

Questions for the article

On ultrasound on June 30, 2017, the doctor said nothing was visible, just a cyst...

I looked at the test, but my result was negative. but so...

The lower abdomen hurts periodically, it swells, it hurts, what could it be...

Please, from what week can you feel fetal movement?...

The size of the fertilized egg corresponds to 3-4 weeks, according to hCG on 2.02 4539, on 4.02...

Pregnancy... but it’s too early to do the test and there’s no delay, but I’m already...

The hCG result is 20.9 mlu/ml. What is my gestational age? latest...

Please. The first day of the last menstruation is 04/20/2016. (conception by...

Accordingly, the period should be 8 weeks, but the ultrasound shows 4-5...

Pregnancy is a time that requires a woman to pay maximum attention to her health.

This is the key to successful pregnancy, easy childbirth and the health of future children. But, as you know, the first weeks of the “interesting situation” pass almost asymptomatically.

Someone finds out about their situation after a couple of months, and then until the end of their term they worry about a couple of glasses of champagne drunk at a corporate party. First of all, women who have recently learned about their pregnancy are concerned about the gestation period.

How to determine the exact duration of pregnancy in the early stages and how reliable are the available methods?

- the first thing a woman thinks about when she wants to make sure of her situation.

The tests are based on determining the presence of human chorionic gonadotropin in morning urine. This specific hormone that begins to be released after implantation of chorionic villi into the uterine mucosa.

It is an almost 100% guarantee of diagnosing pregnancy, and the due date can be determined by the concentration of the hormone.

The test result is traditionally presented by one or two stripes. In this way, the presence of pregnancy can be diagnosed, but its duration remains unknown.

And only with the help of a new product - a digital test (for example ClearBlue Digital) - can you not only diagnose pregnancy, but also find out its due date.

If hCG is detected in the blood, ClearBlue Digital will determine its concentration, and from it the number of weeks that have passed since conception. The test result will be shown on a digital display. “-” means absence of pregnancy, and “+” indicates its presence. If a woman is pregnant, the “+” sign will indicate the number of weeks that have passed since conception.

The test provides 3 options: 1-2 weeks, 2-3 weeks and 3+ (more than three weeks after conception).

The test is so sensitive that it can be carried out not only from the day of the expected period, but also 3-4 days before this date.

However, you can determine the period without a test.

Determining the duration of pregnancy by the date of the last menstruation

If a non-digital home test has confirmed the fact of pregnancy, but you want to find out its duration, you can independently determine this by the date of your last menstruation.

This method is used in obstetric practice. Although in fact, the “traditional” gestation period is two weeks longer than the actual life of the embryo, because conception occurs approximately in the middle of the cycle.

For example, if your period was on February 10, then by the time of the delay (March 10 with a 28-day cycle) the period will be 4 weeks (1.5-2 weeks from the moment of conception).

Determining the period for hCG analysis

Human chorionic gonadotropin is a specific hormone that begins to be released after implantation of chorionic villi into the uterine mucosa.

The presence of hCG is an almost 100% guarantee of diagnosing pregnancy, and the due date can be determined by the concentration of the hormone.

The work of home tests (both digital and showing “two stripes”) is based on the determination of human chorionic gonadotropin in morning urine. There is also a blood test for hCG, which is performed in a clinical laboratory.

The sensitivity of the clinical test and its reliability are much higher than urine diagnostics.

A referral for analysis can be obtained from a gynecologist after a delay in menstruation is detected. Often, the doctor pre-sets the pregnancy period after a gynecological examination, because after the implantation of the embryo, the uterus begins to increase and each week of pregnancy corresponds to its size of the reproductive organ.

However, when going for analysis, you should remember that in some women the increase in hCG may differ significantly from statistical indicators. And this is not always associated with fetal pathology; it may simply be a metabolic feature. In this case, the deadline will be determined incorrectly.

Ultrasound diagnosis of pregnancy

The ultrasound method is the most reliable in diagnosing pregnancy, determining the gestational age and location of the fetus.

Opinions regarding this matter differ, so they try not to prescribe an examination without a good reason.

But ultrasound diagnostics is indicated if there are some chronic diseases of the mother, as well as if the couple was treated for infertility or had experience of unsuccessful pregnancies.

Starting from the 5th obstetric week (about 3 weeks after conception), the fertilized egg is already visible on the screen.

The approximate gestational age is determined by its size. In the early stages, a parameter such as SVD (average internal diameter) is used, and from the beginning of the third month it will be possible to determine the period by the coccygeal-parietal size (CTR).

Basal temperature measurement

If a woman planned her pregnancy, recorded and knows her own physiological cycles, then another home diagnostic method will be available to her. You can continue after the date of ovulation and possible conception.

Above 37°C can most likely indicate pregnancy.

Measuring basal temperature should be done while lying down, after sleep, preferably at the same time, otherwise the data will be uninformative.

All measurements must be entered into a special table, and then a graph of basal temperature must be plotted. So, the embryonic period of your pregnancy will be equal to the number of days following the day when the basal temperature became above 37.

Finding out your pregnancy date as early as possible is the dream of all women, because your plans for the future largely depend on it. If you want to quickly confirm that you are pregnant, do a home test and then get examined at a antenatal clinic.

The sensitivity of tests and the quality of ultrasound diagnostics are constantly improving; you will receive a result that has a high degree of reliability.

Pregnancy is a long-awaited and desired event for many women. And now you will be interested to know everything about your situation: how the pregnancy develops week by week, what is happening in the body. And with the help of a pregnancy calendar you can do this very quickly and easily.

Pregnancy calendar is a convenient and useful service for expectant parents, moms and dads, which will tell you in great detail about pregnancy week by week. He can be your companion throughout your pregnancy right up to the birth itself.

Pregnancy is divided into 3 trimesters:

First trimester - 1-13 weeks after conception
Second trimester - 14-26 weeks
Third trimester - 27-40 weeks

How does the fetus develop during each trimester? Our pregnancy calendar will give you the answer.

Why do you need a pregnancy calendar?

The pregnancy calendar will tell expectant mothers about how their baby changes and grows at this or that stage, how its organs develop, and how the baby gains weight. Our calendar for pregnant women will tell you what to do and what to abstain from at each stage of pregnancy, which doctors you need to visit, how to eat and what lifestyle to lead so that your baby is born healthy.

Also, our online pregnancy calendar will help you find out in what week, using an ultrasound, you can determine if you are having a girl or a boy.

This is exactly the weekly pregnancy calendar that gynecologists use when determining the age and development of the fetus. But there is also the age of the fetus, which differs from the menstrual period of pregnancy by 2 weeks.

In addition, this online pregnancy calendar gives expectant mothers the opportunity to communicate and exchange their feelings and impressions with friends in an interesting position every week of pregnancy. Leave your comments and you will find out who has the same feelings and what they could mean.

But you need to know that every pregnant woman’s body is different, and our calendar does not take into account the individual characteristics of the menstrual cycle, so the calendar contains information that is common to everyone. All dates are approximate, as the length of the menstrual cycle is different for all women and can vary, as a rule, from 24 to 36 days. In addition, you need to take into account that the cycle may be irregular.

Reviews

Galina Chalaya
I approached the moment of conception very consciously and, of course, I take pregnancy responsibly. It is very important for me to know what happens to the baby at each stage of his development. After all, from the moment of conception he is my child, whom I must take care of. Therefore, I am happy to definitely look at the pregnancy calendar and read how my little son is doing in my tummy.

Natalia Semerichko
For me, the most important thing was that while reading about my week of pregnancy, I could chat on the forum and discuss my feelings with other expectant mothers who are at the same stage.

Maria Krylova
This calendar helped me learn a lot of useful information about my future baby. During this period, I was most interested in how it was in my tummy. After all, this pregnancy was my first. Very convenient and useful service. Thank you very much!

Send your reviews about the Pregnancy Calendar to editorial@site

Nowadays, the development of medicine and scientific technologies makes it possible to accurately diagnose and predict the state of human health. This also applies to pregnancy. Just a few decades ago, no one could predict the exact date of birth or the gender of the baby, but today this is quite common information that a pregnant woman can receive during a routine examination with a gynecologist. Currently, you can determine how many weeks of pregnancy you have using several methods, and without the help of a doctor. The gynecologist will provide updated data after the ultrasound. So, the article will talk about ways in which you can set the period of an interesting situation.

Why do you need to know your gestational age?

Firstly, to calculate the estimated due date. Secondly, in order to competently monitor the baby’s development, correct developmental and developmental delays in a timely manner. Thirdly, to determine the start date of maternity leave. Knowing the exact duration of pregnancy allows you to timely identify abnormalities and pathologies of the baby’s development (for example, Down syndrome).

You should know that there is a difference between true and obstetric terms. Obstetricians-gynecologists count the beginning of pregnancy from the day when the last menstruation began. This is justified by the fact that this is the moment when the egg cell begins to mature, which, as a result of fertilization, is introduced into the uterus and begins to develop. The duration of pregnancy during obstetric period is 40 weeks, or 280 days. But there are also deviations, it all depends on genetic factors. It affects the period at which the woman herself was born, as well as the father of the child.

The true term differs from the obstetric term by two weeks, while the countdown of pregnancy begins from the day of ovulation or conception. So, let's look at a variety of methods for determining how many weeks you are pregnant.

Pharmacy test

The most common way to determine how many weeks pregnant is a test. It can be used to determine the presence of pregnancy. They are all based on analysis of the presence of the hCG hormone, the content of which increases with increasing pregnancy. The more sensitive the test, the earlier the pregnancy can be confirmed. The highest quality and most sensitive test can establish pregnancy approximately 7-9 days after the expected conception.

Types of tests:

Reservoir. The test is placed in the test reservoir, and a strip on the test determines how much urine is needed to produce an accurate test.
Cassette. It resembles a device with a depression in the middle, into which a drop of urine is added using a pipette.
Jet. When urinating, it must be placed under a stream of urine.
Digital. It is a device with a hole that is wetted with urine.
Strip test (the most common). It is a strip that is immersed in any container filled with urine to the level specified in the test.

Method for determining gestational age by ovulation date

During ovulation, a mature egg from the ovary begins its movement through the fallopian tube, and it is at this time that there is a maximum chance of becoming pregnant. By the date of ovulation, you can determine the true duration of pregnancy, and it usually occurs in the middle of the cycle.

But how to determine how many weeks of pregnancy you have by ovulation? How to find out when it happened? There are several ways to determine the onset of ovulation:

Using ultrasound.
At home, using tests that can be purchased at the pharmacy.
By measuring basal temperature. At the beginning of the cycle it is below 37 °C, the day before the start of ovulation it decreases, and on the day of ovulation and the entire second phase of the cycle until menstruation it will remain 37 °C and above.

There are hypersensitive women who can detect ovulation by their sensations: abdominal pain, increased discharge, increased libido, and so on. It is much easier for these women than for others to determine on their own the period of an interesting position.

Method for determining the gestational age based on the last menstrual period

The most common way to determine how many weeks of pregnancy is the obstetric method - by the day the last menstruation began. 280 days are added to this day and the approximate date of birth is established. That is, if, after a delay, you go to the antenatal clinic with confidence that the pregnancy is 5 weeks, the doctor will set the period to 7 weeks - this is the obstetric period.

Female doctor

The most accurate way to determine how many weeks of pregnancy is to consult a doctor. If you contact in the early stages (4-5 weeks), it will not be difficult for the doctor to determine the exact date. He will measure the uterus and then calculate the gestational age. For example, at 4 weeks its size is approximately the size of a chicken egg, at 8 weeks it is the size of a goose egg. An experienced doctor is able to determine the period during a vaginal examination with an accuracy of up to a day.

However, after 8-12 weeks, based on the size of the uterus, it is problematic to determine the period of an interesting position. Since from the second trimester in women, the size of the uterus is very individual. That is why, when the question is asked on forums about how many weeks it is possible to determine pregnancy and when it is better to contact a gynecologist, the answer from doctors is always this: the sooner you go to the antenatal clinic, the easier it is to determine the duration of pregnancy.

By ultrasound

How many weeks does ultrasound determine pregnancy? Here a lot depends on the doctor who describes the results. But the most correct data are those obtained by ultrasound before the 12th week of pregnancy. They can be used to determine the date of expected birth. At this time, they are based on the measurement of the fertilized egg and its diameter. In the second and third trimesters, they are based on determining the circumference of the baby’s head, the average diameter of the tummy and chest. But the most accurate information is considered to be obtained by measuring head circumference.

It is believed that the longer the pregnancy, the more difficult it is to determine using ultrasound. Because each child is individual, and at the end of pregnancy, its parameters may differ greatly from the standard ones.

At the baby's first move

There is another method. How many weeks can pregnancy be determined? This can be recognized by the baby's movements. Primipara women begin to feel the baby's movements for the first time at about 20 weeks. Those women who have already given birth feel their baby a little earlier - at 17-18 weeks. This method of determining the gestational age is not entirely accurate. There are women who begin to feel the baby's movements in their first pregnancy at 16 weeks. Most often this happens in thin girls.

By basal temperature

The method is suitable for those women who constantly monitor their basal temperature, and not just on the day when they suspect pregnancy. The method consists of measuring body temperature in the rectum (rectally), vaginally or orally for 5 minutes every day. The main condition is that this is done immediately after waking up and before getting out of bed. You should always use only one permanent measurement site, for example, orally. What is the essence of this method?

The menstrual cycle is divided into two phases: follicular and luteal. The first continues from the beginning of menstruation until ovulation, the second after ovulation. In the first half of the cycle, basal temperature is always lower than during the luteal phase. During ovulation, the temperature rises and then gradually begins to decrease until the onset of menstruation. But if the temperature in the second half of the cycle does not decrease, but even increases slightly, then this is a clear sign of pregnancy. How many weeks later can pregnancy be determined using this method? Literally after a while it will become clear that the temperature is not decreasing, and by the time of the delay it will already be reliably known about the interesting situation.

By hCG

This is the most accurate method. It allows you to detect pregnancy already 8-10 days after conception. In a woman’s body, the hCG hormone begins to be produced immediately after the implantation of a fertilized egg. This hormone is present in the urine and blood of the expectant mother, and to determine the presence of pregnancy, you can donate blood for analysis or take a test.

It should be borne in mind that the period of pregnancy in terms of the level of hCG in the blood does not coincide with the obstetric period, since this hormone begins to grow from the moment the embryo is fixed (that is, from the true stage of pregnancy).

Traditional methods

The urine of a pregnant woman is alkaline; if you add soda to the morning portion, it will settle. But if the woman is not pregnant, the urine will bubble as a result of the reaction.

Online calculators

There are a huge number of calculators on the Internet with which you can create your own pregnancy calendar. It is necessary to enter the day of the beginning of the last menstruation into the window of such an online test, after which the program will provide a detailed calculation of the height and weight of the fetus by week.

Instead of a conclusion

All of these methods can accurately determine the presence and duration of pregnancy. But it should be borne in mind that the baby, even with the most correct calculations, may be born later or earlier than the due date. Natural birth can occur from 38 to 40 weeks, but premature birth can occur or, conversely, the baby can be born at 41 weeks. Everything is individual and depends on many factors, the main of which are genetic predisposition and the presence of chronic diseases. Be that as it may, the mother’s main task is to do everything that depends on her so that the pregnancy proceeds well and a daughter or son is born safely.

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 of the last menstruation, from which it is calculated, is important. 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 at different stages of 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 a large fetus, multiple pregnancies, or in case of abnormal fetal position, and decreases in the case of a small fetus, or with a low standing of the presenting part of the fetus (if there is a threat of miscarriage). 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 is not yet determined, the period is set based on the size of the fertilized egg.

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. It is impossible to determine the exact date of birth for each specific 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(at 30 weeks, 10 weeks are added to this number);
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.