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From what day are the weeks of pregnancy counted. Is the time period specified with help accurate? What is the gestational age

A woman, having learned from a doctor about her desired pregnancy, will definitely want to find out the “age” of the future crumbs. There are several ways to determine the date of birth of the baby, both independent and with the help of specialists. How to correctly calculate the gestational age, as well as how the real term differs from the obstetric one, we will try to tell in this article.

The obstetric term, which is set by gynecologists at the first appointment with the expectant mother, differs markedly from the real one, but is the most accurate parameter. It is believed that pregnancy occurs at the moment of direct conception or fertilization of the mother's egg. This usually happens around the middle of the menstrual cycle, so if a woman knows the day when the egg leaves the follicle and ovulation begins, then she can accurately calculate the gestational age.

Basal body temperature (BT)

To do this, you need to daily, remaining in a horizontal position in bed, measure the temperature by the rectal method. After menstruation, in the period of 10-14 days, it most often does not exceed 37 degrees, and during and after ovulation, it can rise to 37.2-37.3 degrees. The day of conception does not always coincide with the time of sexual intercourse. The sperm cell has the ability to survive from three to seven days in anticipation of the appearance of the egg from the ovary. And the lifespan of the mother cell itself is limited to 24 hours. Therefore, if sexual intercourse occurred 5-7 days earlier than ovulation occurred, then conception can occur 5-7 days later than coitus. Therefore, experts argue that this method of counting for determining the embryonic period is not entirely accurate. In addition, each woman, due to her individual characteristics: a certain menstrual cycle, the day of ovulation and the possibility of re-emerging an egg from the ovaries, will have her own fetal development period, which cannot be determined one hundred percent.

In obstetric practice, the date of the first day of the last menstruation is used. The error of this method is only 7-14 days. The obstetric period is calculated in two ways: 10 average menstrual cycles (28x10) or 280 days are added to the first day of the last menstruation; in the second case, 3 months are subtracted from the same date and 7 days are added (Negele's formula). In the ideal case, when the exact date of ovulation is known (days 12-16 of the menstrual cycle), 264 days can be added.

Note! At the appointment with the gynecologist, the expectant mother will find out the obstetric period, since doctors do not take into account the rest of the calculations.

Ultrasound procedure

For many years, the ultrasound method has been quite actively used in the diagnosis of fetal development. The most accurate gestational age is obtained using studies conducted at the earliest stage of pregnancy - up to 8 weeks. The development of healthy embryos these days is identical and it is possible to determine the gestational age up to a day by the size of the fetus. In the future, the children begin to show their individuality, any healthy fetus may have minor deviations (for example, growth is slightly below normal or the size of the head is slightly larger). If this difference fits within a period of no more than 7-10 days, then doctors usually do not take this circumstance into account, but if it is a period of two or more weeks, then doctors diagnose intrauterine growth retardation and recommend paying attention to proper balanced nutrition , walks, a healthy lifestyle that will help normalize the development of the embryo.

A gynecologist's consultation on the first day of pregnancy delay is usually not needed, since the doctor will not yet be able to determine whether the uterus is enlarged as a result of PMS or conception. The perceptible growth of this female organ in connection with pregnancy begins only at the end of the first trimester. In the second or third week of delayed menstruation (for a period of 5-6 weeks), the uterus reaches the size of a chicken egg, at 8 weeks - goose, at 10 - usually acquires the size of a female fist.

HCG and gestational age

How to correctly calculate the gestational age using human chorionic gonadotropin? Ideally, a blood test from a vein is not used to determine the timing of an “interesting situation”, but for the early diagnosis of possible complications. In the second week, an approximate table of hCG values in the blood of a pregnant woman contains a parameter from 25 to 150 IU per ml, and in the eighth - up to 70 thousand IU per ml. Serious deviations from the table values indicate a serious pathology, such as missed or ectopic pregnancy.

First fetal movement

Doctors say that for the first time pregnant women, the feeling of the inner presence of the baby occurs exactly at 20 weeks of pregnancy, for re-pregnant women - at 18 weeks. This date is an important step in the correct calculation of the gestational age. It is easy to notice the movement, especially when lying on your back.

Uterine length

Starting from the second trimester of pregnancy, gynecologists measure the length of the uterus with a centimeter tape in the patient lying on the couch. In a future mother, the uterus adds about a centimeter in size every week. In addition, there are special tables that can be found in manuals on gynecology and obstetrics.

Heart tones

The embryo's heart begins to beat already at four and a half weeks (or 2-3 weeks after a woman's period is missed). This is noticeable in early ultrasound examinations. Through an obstetric stethoscope, the fetal heartbeat is heard much later, approximately after the date of the beginning of the movement of the future crumbs. Poor hearing can be caused by a placenta located closer to the anterior wall of the uterus or significant abdominal deposits of adipose tissue.

No matter how hard you try to correctly calculate the gestational age to the day, most likely it is unlikely to succeed. This can only be done hypothetically. Your baby will be born into the world only according to the laws of Mother Nature, when he is ready for this. Good luck in this difficult and noble cause!

Video

You can learn more about calculating the gestational age from the following video:

The formation of an egg and its release from the ovary occurs approximately in the middle of the cycle (12-16 days before menstruation). This process is called ovulation. In the absence of ovulation, pregnancy is impossible.

During intercourse after ejaculation (ejaculation), sperm enter first into the vagina and then into the cervix. Spermatozoa enter the cervix already 30 seconds after ejaculation, and already 5 minutes after entering the cervix, the sperm enters the fallopian tube. Being in the female genital tract, they can remain viable and fertile and “wait” for ovulation for 3 days (although occasionally the fertilization ability lasts up to 5-7 days). The egg after leaving the ovary lives for 24 hours. Therefore, conception is possible if sexual intercourse occurred from 3 days before ovulation and ending with a day after.

In the ovary, after the release of the egg, a corpus luteum is formed. This is a hormonally active formation that secretes the hormone progesterone, which is necessary for the normal development of pregnancy. If fertilization does not occur, the corpus luteum resolves. If pregnancy occurs, the corpus luteum functions until the 16th week of pregnancy.

After leaving the ovary, the egg enters the abdominal cavity, then it is captured by the villi of the fallopian tube (fimbria) and thus enters the tube. It is in the tube that the egg meets the sperm and their nuclei merge, a zygote is formed. The process of fusion of the egg and sperm is called fertilization. Only one sperm is involved in the fertilization of one egg. Sometimes there is a formation in the cycle of 2 or even 3 eggs (especially if ovulation stimulation courses were carried out for medicinal purposes). In this case, if each of these eggs is fertilized, pregnancy may occur with fraternal twins or triplets.

Pregnancy begins from the moment of fertilization. However, the obstetric period is considered from the first day of the last menstruation. This is due to the fact that the woman's body begins to prepare for a possible pregnancy from the first day of the cycle: the egg begins to mature in the ovary, the uterine mucosa is formed to become ready for implantation. Childbirth occurs on average after 40 weeks (10 lunar months) counting from the first day of the last menstruation.

Feelings of a woman during pregnancy

In the early period (before the delay of menstruation), almost all signs of pregnancy are only hypothetical, that is, doubtful, individually not informative. All of these features are subjective. Sometimes a woman finds herself with any of them, even if she is not pregnant at all. Often this happens if a woman is very much looking forward to pregnancy, and inspires herself that she feels something special.

Some women have no early signs of pregnancy at all, and they may not notice any changes in their well-being for quite a long time.

* The most well-known symptom associated with pregnancy is nausea. In some women, it appears already at 1-2 weeks of pregnancy. However, this is rare, most often nausea appears after the 4th week.

* Almost always during pregnancy, a woman feels engorgement of the mammary glands. The chest becomes as if swollen and more sensitive than usual. Some women feel this as early as a week after conception.

* One of the first signs of pregnancy is irritability and rapid mood swings. Pregnancy affects the nervous system from the very first days. However, a woman can be nervous and irritable and because of the very expectation and uncertainty. In many women, this symptom is generally observed as part of the premenstrual syndrome before each menstruation.

* There may be mild aching pains in the lower abdomen, in the sacrum and lower back. Usually they are somewhat different in character from those that precede menstruation.

* Taste changes may occur (eg the well-known salty cravings). Intolerance to some smells is possible, including those that you liked before.

* A fairly common symptom of pregnancy is fatigue and drowsiness. Although, if you often felt tired and tired before and did not get enough sleep, you may not notice it. In addition, such signs may be due to a lack of vitamins or when the weather changes.

* Body temperature may rise slightly (up to about 37 degrees). In this case, there may be a slight malaise, as with a cold.

* A woman's intuition can also be attributed to the presumptive signs of pregnancy. Some women claim that they feel that they are pregnant, although they do not notice any changes in well-being.

* Most often, a woman begins to suspect pregnancy when the next menstruation is delayed. However, occasionally, menstruation can come on time even if there is pregnancy, although in this case, spotting is often more meager than usual. There may be another situation - no menstruation, but no pregnancy. Even with a regular cycle, small failures are sometimes possible. This can be caused by stress, weather changes, chronic lack of sleep, a diet with significant weight loss.

Most pregnancy tests show a positive result from the first day of a missed period. However, there are now tests that can show the presence of pregnancy starting 4 days before the expected period. However, the earlier you test, the greater the chance of false negative results.

How does the future baby develop?

Sex cells (sperm and egg) contain half the set of chromosomes. When they merge, a zygote is formed, which already has a complete set of chromosomes, that is, its own unique genotype.

Fertilization and the first 3 days of embryo development occur in the fallopian tube. The first division of the zygote (into 2 cells) ends 30 hours after fertilization. Before day 3 of development, any cell can give rise to any organ. Cell separation at this stage can lead to the development of identical twins.

The embryo in the form of a group of dividing cells enters the uterus only on the 4th day after fertilization. The transport of the embryo to the uterus occurs due to peristaltic contractions of the tube wall. The embryo at this stage is called a blastocyst. There are 2 types of cells in the blastocyst. Some of the cells located in the center form an embryoblast, from which the embryo itself is subsequently formed. And those that are outside form the trophoblast - the nourishing shell of the embryo.

Attachment of the embryo to the wall of the uterus is called implantation. Implantation occurs 5-9 days after fertilization and lasts about 40 hours. From the moment of implantation of the embryo, the embryonic period begins, which lasts until the 8th week.

After implantation, the chorion develops from the trophoblast, from which the placenta is subsequently formed. Thanks to the chorion, the circulatory system of the fetus and mother communicates and the fetus is nourished.

From the embryoblast, 2 germ layers (ectoderm and endoderm), a yolk sac and an amnion are formed. Later, a third germ layer, the mesoderm, forms between the ecto- and endoderm. From these three layers, various types of organs and tissues develop.

The amnion is a hollow organ filled with fluid. This liquid surrounds the embryo from all sides and protects it from drying out and mechanical influences, and also protects against infection. From the amnion, a fetal bladder with amniotic fluid is formed. The yolk sac performs a hematopoietic function until the 7-8th week of pregnancy, and then it dissolves.

In the period from 18 to 28 days after conception, the neural plate is formed, the edges of which close and form the neural tube. It gives rise to the nervous system. On the 17-20th day, the system of bone vertebrae is laid. From the beginning of the fourth week after fertilization, the liver appears, the rudiment of the respiratory system appears. At the 4th week, the first signs of a heart appear.

Complications that may occur during this period

At the pre-implantation stage (that is, before the embryo attaches to the uterus), developmental disorders follow the “all or nothing” principle. This means that either the adverse effect led to the death of the fetus (in this case, the woman may not even know that she had a pregnancy), or the fetus survives and develops normally. You can read about the impact of harmful factors during pregnancy in the article.

The end of the first - the beginning of the second week of development - this is the first critical period of development during pregnancy. Unfavorable factors during this period usually lead to the death of the embryo (then either spontaneous miscarriage or regression of pregnancy occurs). If the pregnancy continues, then the negative factor did not influence.

The second critical period falls on weeks 3-8 of development. In this case, the action of an unfavorable factor often induces gross malformations, or, again, the death of the embryo may occur.

A complication of pregnancy at an early stage may be the formation of an ectopic pregnancy. This happens when the embryo does not move into the uterus on the 4th day, but continues to develop in the tube.

In order for the pregnancy to proceed favorably from the very beginning, it is important to create favorable conditions for the unborn baby already at the planning stage. Therefore, it is necessary to change your lifestyle - give up bad habits, eat right, spend more time in the fresh air. Contact your antenatal clinic doctor to undergo the necessary examination before pregnancy to identify risk factors. Also, the doctor will prescribe the necessary vitamins and, if necessary, other medications that prevent fetal malformations and pregnancy complications.

Read more about how the baby develops in the mother's tummy, read in

(duration 28 days), or 280 days. In fact, these terms fit into 9 calendar months, plus seven days. Therefore, it is customary to talk about 9 months. The birth of a baby at 38-42 is considered normal if there are none indicating immaturity or overmaturity. If the child was born later than this period, then it is considered post-term, otherwise - premature.

Obstetrician-gynecologists start counting the gestational age from the first day of the last menstruation. Usually, the actual period is 13-16 days less, since conception occurs approximately in the middle of the menstrual cycle, i.e. at the time of ovulation. However, to avoid confusion, doctors start counting the gestational age 2 weeks ahead of the date.

If you do not know the exact date of conception, then it is most correct to count the weeks of pregnancy based on the results of an ultrasound scan. Scheduled research is carried out at 12-13. As a rule, it coincides with the deadline set at the first appointment. But, if there are discrepancies, then it is better to focus on the period set with the help of ultrasound.

In some cases, there may be a discrepancy between the size of the fetus and the gestational age. For example, as a result of polyhydramnios, the presence of tumors, etc. These data are taken into account by specialists in the study. In this case, they put the number of weeks of pregnancy, obtained from the calculation from the first day of the last menstruation, and with the help of ultrasound at later times, they correct it.

How do doctors determine the duration of pregnancy?

For women who come to a medical facility and claim to be pregnant, the gynecologist first of all asks when the last menstruation was. It is from this date that he will count. Interesting, right? Fertilization has not yet come, since it occurs during ovulation in the middle of the cycle, and obstetricians start counting from such an early date.

This method of determining the duration of pregnancy and childbirth is called " obstetric». True the period of an interesting position is about 2 weeks less than the period that the doctor tells the pregnant woman. The minimum period for determining pregnancy by this method is 2-3 weeks.

You can find out the period by the results of ultrasound. Their accuracy will be less in the later stages, because each baby develops in the mother's tummy in its own way. The doctor determines the gestational age by the size of the fetus. The following indicators are measured:

biparietal size, determined between the temporal bones (BDP);
fronto-occipital size (LZR);
head circumference (OG);
abdominal circumference (OC);
thigh length (DLB);
chest diameter (DRD), etc.

Each week is characterized by certain values of the above criteria. The gynecologist uses a special table for determining the timing of pregnancy to calculate.

The doctor can determine the term of an interesting position by the size of the uterus during a gynecological examination. For example, at the 4th week of pregnancy, the organ can be compared with a chicken egg, and at the 8th week - with a goose egg. Later, it is difficult to establish the term according to the size of the uterus.

How else do doctors determine the duration of pregnancy? For example, a method is used to determine the duration of the position along the length of the uterus. A tazomer or centimeter tape is used. As a rule, the number of weeks is equal to the length of the uterus. For example, during the measurement, it turned out that the length of the uterus is 34 cm. This means that the period is 34 weeks. To obtain reliable results, a woman is advised to empty her bladder before visiting a doctor.

How to determine the gestational age at home?

A pregnant woman can independently calculate the duration of her interesting position without the help of doctors. How to find out the gestational age at home? There are several ways:

according to the last menstruation;
by date of conception
at the first stirring of the crumbs;
using an online calculator.

1. How to determine the gestational age by the last menstruation?

The easiest way that doctors and many women find out the gestational age is by the last menstruation. How to determine the most gestational age by the last menstruation? Between the date of the beginning of menstruation and the date of the calculation, it is necessary to calculate the number of weeks. This will be the duration of the pregnancy.

By the date of the last menstruation, it is convenient to calculate the date of birth. There is a special Nagel formula. From the date of the last menstruation, 3 months are counted back and 7 days are added.

The calculation of pregnancy by the last menstruation is a fairly simple, but inaccurate method, since it is a couple of weeks longer than the true period.

2. How to determine the gestational age by the date of conception?

Recall that conception occurs approximately in the middle of the cycle after the release of a mature egg from the ovary (ovulation) during the day. The method of calculating the gestational age by the date of conception is suitable for those women who know exactly when they ovulated. The gestational age is determined by weeks. The countdown is from the date of ovulation. Average values can also be used (for example, with a 28-day cycle, ovulation approximately occurs on day 14, i.e., in the middle of the cycle). And how to determine the gestational age with an irregular cycle? In such cases, approximate values \u200b\u200bare not suitable.

The moment of release of an egg ready for fertilization can be determined using special tests, basal temperature or ultrasound results. Some women determine ovulation by how they feel (by the presence of pain in the lower abdomen, abundant discharge from the penis, increased libido). If the date of ovulation (and, accordingly, the date of conception) is unknown, then using the method of determining the gestational age by the date of conception will not work, since the results will not be accurate.

3. How to determine the gestational age by the first movement?

The baby begins to move in the tummy of the mother, whose pregnancy is the first, from the 20th week. Multiparous women begin to feel movements from the 18th week.

It is worth noting that using this method it is not always possible to find out the exact time. Some women feel the first movements much earlier than the indicated weeks, and some vice versa later. Most doctors note that the fair sex often confuses the first movements with the "work" of the intestines, because it is known that many pregnant women suffer from increased gas formation.

4. How to determine the gestational age using a calculator?

To calculate the gestational age, you can use the calculator, which is presented below. His work is based on the method of determining the period by the last menstruation, which was described above. How to determine the gestational age using an online calculator? In order to use it, you need to know the date of the beginning of the last menstruation, the average duration of the menstrual cycle and the luteal phase. The results of the calculation will be known immediately.

Summing up all of the above, I would like to note that many women are interested in the question of how to accurately determine the gestational age. However, with almost all of the above methods, it can not be calculated accurately. The only exceptions are cases when a pregnant woman knows the exact day of ovulation. Is it necessary to know the absolutely exact term of an interesting position? It is worth noting that it is not so important. Deviations of a few days or a week will not play a big role, so do not be afraid if the exact day of ovulation and conception is not known.

Answers

What is the most common question asked by pregnant women? "What time frame are you on?" It turns out that answering it correctly is a whole science. Let's try to master it.

Terms - obstetric and embryonic period

When registering for pregnancy in the antenatal clinic, the doctor will determine and use obstetric term. Its countdown starts from the first day of the last menstruation, and the calculation is carried out in weeks. The average full-term pregnancy according to this calculation of terms lasts 40 weeks (280 days). Previously, such a period was considered in months - the well-known 9 months (actually 9 months and 7 days). Currently, the question "What month are you on?" can drive a pregnant woman into a stupor - she is much more willing to tell you what her week is like!

Interestingly, at determining the duration of pregnancy by menstruation in the first 2 weeks, there is no such period of pregnancy as such, because conception has not yet taken place.

Another way to calculate the term is by conception. It is also called embryonic period or true. Most often, it is difficult to say exactly when the conception occurred - the union of the egg and sperm - rather, we can talk about the known date of ovulation or proximity, as a result of which a new life was born. Such terms can be indicated in the ultrasound protocol or on the results form (hCG). Clarify this point to avoid confusion and unnecessary worries.

Correction of the obstetric period for late and early ovulation

The obstetric term is calculated based on the "ideal" 28-day female cycle with ovulation on day 14. If it is known that ovulation occurred later or earlier, it would be logical to correct such a period. To do this, you need to determine the conditional start date of the "correct" menstruation - subtract 14 days from the known date of ovulation. From this day on, count the "legitimate" 40 weeks. Accordingly, real late ovulation pregnancy will be less than calculated simply from the date of the beginning of menstruation.

Determining the gestational age by ultrasound

A good help in determining and clarifying the timing of pregnancy is.

At the very beginning of pregnancy, when you may not even be sure about it yet, the fetal egg is measured with the help of an ultrasound study. Unfortunately, the average internal diameter (SID) of the fetal egg can tell about the gestational age very approximately, since possible fluctuations in terms for this parameter can be up to 1.5 weeks, both up and down.

When the embryo begins to be visualized in the fetal egg, the coccygeal-parietal size (KTR) is measured. This is the maximum distance from the head end (temechka) to the coccyx. Measurements are taken at the moment of maximum extension of the embryo. If you have an irregular cycle, or you are not sure when you ovulated, this size is the best way to determine your baby's fetal age. This indicator is used for determining gestational age with Ultrasound during the first trimester.

Table 1. Coccyx-parietal dimensions of the embryo/fetus in the first trimester of pregnancy

Pregnancy period, weeks	KTP value, mm

In the II and III trimesters, several indicators are used at once to determine, but rather to clarify the timing of pregnancy using ultrasound. This is the biparietal size (BPR) - the size between the temporal bones, the circumference of the abdomen (OC) and the length of the femur / thigh length (DB).

Table 2. Fetometric parameters in the II and III trimesters of pregnancy

Pregnancy period, weeks	Biparietal size, mm	Abdominal circumference, mm	Femur length, mm

The greatest accuracy in determining the duration of pregnancy in the II and III semesters gives the complex use of the three parameters indicated in the table. Modern ultrasound machines independently calculate the period, taking into account all these indicators.

It must be remembered that the longer the gestational age, the more the size of a particular baby may differ from the “table” ones - individual traits begin to appear more and more clearly. So, before the 11th week, the measurement of CTE gives an accuracy of ± 2-3 days, after the 11th week - 2-5 days, before the 20th week, the measurement of BDP can give an error of up to 7 days, and after this period - up to 11 days . Therefore, you should not panic if your child's indicators differ from the average by a couple of millimeters, and at a later date by a couple of centimeters.

Determining the expected date of birth (ED)

So, in order to calculate when to expect the birth of a baby, 280 days (or 9 months and 7 days) must be added to the first day of the last menstruation. It is a little easier to count backwards - from the date of the first day of the last menstruation, you need to subtract 3 months and add 7 days. In this case, do not forget to add one year. This is a brain workout.

There are many services on the Internet where, by entering the start date of the last menstruation, you will receive an accurate calculation of the expected due date.

In fact, not many women give birth on this scheduled day. It is considered that the child was born at term if the birth occurred from the 38th to the 42nd week of the obstetric term. So your baby has a lot of choice when exactly to be born.

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