The doctor in the LCD talks about some obstetric weeks of pregnancy, the ultrasound sets a completely different period, and according to your calculations, the third is obtained. And how can an inexperienced future mommy not get confused here. In fact, everything is not so difficult, you just need to deal with some of the nuances.
What is an obstetric term and why is it needed?
Obstetric weeks of pregnancy include the period from the first day of the last menstrual period before pregnancy until the expected due date (PDD). The obstetric period is 280 days or 40 weeks, or 10 obstetric months (a month is 28 days). Obstetric weeks of pregnancy are counted even when conception has not yet occurred, but the processes of maturation and release of the egg have successfully passed.
The definition of obstetric weeks is necessary for the convenience of calculating the timing of pregnancy. After all, no doctor can say for sure when a woman had ovulation and, accordingly, conception. And the woman herself can, of course, guess about the possible day of conception, but not be completely sure of it. Meanwhile, as the date of the beginning of the last menstruation is remembered by almost all the fair sex.
What is embryonic term and ultrasound term of pregnancy?Fetal term is the life span of your baby, first as an embryo, and then as a fetus. The embryonic period lasts approximately 265-266 days (38 weeks or 9 normal months).
Ultrasound examination determines the estimated duration of pregnancy based on the available size of the baby, while relying on the standard indicators of its development at embryonic (up to 12 weeks) and obstetric (after 12) weeks. The ultrasound timeline is rather imprecise. The size of the fetus, like the size of an adult, is individual, small children are born, heroic children are born, a slight deviation (no more than 2 weeks from the norm for the corresponding week of pregnancy) is allowed. Nevertheless, the definition is very important, a significant deviation from the standard indicators indicates various pathologies in the development of the baby.
How to count obstetric weeks of pregnancy?
The doctor should tell the expectant mother about what and how the obstetric weeks of pregnancy are considered. But if suddenly he did not cope with his task, and you forgot to clarify this point with him on your own, the following information is for you.
So how to calculate obstetric pregnancy weeks? It's pretty simple. Take the calendar, remember the date of the first day of the last menstrual period, count from this day (including with it) the number of days or weeks (as you like) until today, you get. If you counted in days, do not forget to divide the resulting number by seven. If you want to know the date of the expected birth, use the same scheme to calculate 280 days. You can determine the PDR in a different way, namely: according to the same calendar, count three months from the first day of the last menstruation back and add 7 days.
How are obstetric weeks and fetal weeks different?Based on the above, the difference between obstetric and embryonic weeks pregnancy consists in the order in which they are counted. Obstetric term 
is 280 days (counted from the last menstruation). Meanwhile, embryonic lasts approximately 265 days (count from the day of conception).
If a woman's menstrual cycle was regular and stable, then with a high percentage of probability it can be assumed that ovulation occurred in the middle of the cycle and in the middle of the cycle, respectively, conception occurred. That is, the difference in time between obstetric weeks of pregnancy and embryonic in a healthy woman with a regular menstrual cycle lasting 28-30 days is within two weeks. In women with an irregular cycle, the embryonic period can only be guessed at.
So, your suspicions about pregnancy have been confirmed. And now you are most concerned with the question: when did the miracle happen? When did the conception take place, and when is the birth now expected?
Obstetric and actual gestational age
The gestational age is calculated by obstetric weeks, there are forty of them (in the normal course of pregnancy). It is a mistake to think that they are calculated from the moment of conception. The starting point is the start date of the last menstrual period, the one that ended with conception.
During the first obstetric week of pregnancy, your future child exists, one might say, only in the form of a maturing egg. During this period, the endometrium of the uterus is also rejected and prepared for a new cycle.
During the second week from the onset of menstruation, the ovarian follicle, which releases the egg, matures and bursts. Ovulation occurs on day 13-16, and the following two to three days - the best time to try to conceive a child.
If it succeeds and the sperm has joined with the target, then at the end of the third week from the beginning of menstruation, the fertilized egg divides and moves along the tube to the uterus. The third obstetric week is the first week of the actual (embryological) pregnancy, which is counted from the moment of cell fusion.
During the fourth obstetric week (from the beginning of menstruation), a fertilized egg - a blastocyst - is implanted into the endometrium and, with a successful pregnancy, forms a fertilized egg. At this time, the corpus luteum in the ovary begins to "work" in pregnancy, and the change in hormonal levels already affects your well-being.
In the fifth week after the last menstruation, the next one should already begin. If this does not happen, suspicions about pregnancy increase.
Determining the actual timeframe using tests
By the fifth obstetric week, the concentration of the hormone hCG (human chorionic gonadotropin) in the urine reaches such a level that a rapid test can show two stripes. But this does not always happen, or the second strip may be barely visible. This happens when ovulation is later than usual. As soon as both strips on the test become equally bright, you can be sure: the pregnancy is uterine, the embryological (actual) period is two to three weeks.
If you remember the exact date of intercourse that led to conception, then add five more days to this number to establish a starting point for the actual pregnancy. You may have even felt the attachment of the blastocyst: sometimes it is accompanied by general deterioration feeling of well-being, lethargy, a slight increase in temperature.
Be that as it may, when registering, the gynecologist will still ask you about the start date of the last menstrual period, since it is on obstetric weeks that all examinations are prescribed, as well as going on maternity leave (hospital for pregnancy and childbirth). The due date is indicated exactly 40 weeks after the start of the last menstrual period.
To make sure that the pregnancy is uterine and developing normally, the obstetrician-gynecologist may prescribe you an ultrasound of the pelvic organs. The direction will indicate the period in obstetric weeks, but the specialist on the study will most likely indicate a shorter period - just those two weeks that precede conception. This should not scare you, ultrasound of early pregnancy is a very inaccurate procedure, the ovum and embryo can be of different sizes and shapes with their normal development.
With further examinations, the period indicated by the doctor at the site and the ultrasound period will be equal to 20-23 weeks. The duration of the cycle for women is different, while the average period of 28 days is taken to calculate the period for obstetric weeks, ovulation also does not always occur in the middle of the cycle, which explains the discrepancies in determining the duration of pregnancy.
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During the carrying of the first baby, a woman is faced with many questions. Most of them are related to how her state of health should be, and how to react to certain changes in her body. But in addition, many expectant mothers are faced with the problem of determining the exact duration of pregnancy. And the numbers given in the results of ultrasound and gynecological examination may differ. Usually, when calculating, doctors use the obstetric gestational age, but in some cases the real term can also be used, let's try to figure out which calculation is right for you? And how to correctly calculate the gestational age?
In most cases, it is not possible to determine the exact date of conception, which is why, to understand the duration of pregnancy, doctors have always focused on the date when the last menstruation began. This method of calculating the gestational age is called obstetric. However, such calculations have nothing to do with the date of conception, because a new life arises much later.
As you know, pregnancy occurs at the moment when the egg is fused with the sperm inside the fallopian tube. In most cases, such an event occurs exactly on the day of ovulation or within a day after its completion. Thus, calculating the gestational age from the moment of ovulation, it is possible to more or less accurately determine the actual period of fetal development.
However, this technique is far from always suitable for further monitoring of the course of pregnancy, since in many women ovulation does not always occur exactly in the middle of the cycle. In absolutely healthy women, this event can happen a little ahead of schedule or, on the contrary, a little later. Therefore, the real (embryonic) gestational age is often simply impossible to determine.
The obstetric period began to be calculated a long time ago, when there was no information about the features of the course of pregnancy, as well as about ovulation. Many years ago, the only symptom of the onset of conception for a woman was the absence of menstruation, therefore, the period was counted from the moment of the last menstruation.
Obstetric gestational age and real calculation - the difference
A typical menstrual cycle lasts four weeks - twenty-eight days. In this case, conception falls somewhere on the fourteenth day, just at this time ovulation is maximum possible. Accordingly, the actual period of development of the fetus and obstetric will differ by about two weeks.
Accordingly, if the doctor tells you about the gestational age of four weeks, then the real age of the embryo is only two weeks.
However, depending on individual characteristics, such a difference can be greater or less.
If the length of your menstrual cycle slightly different from the standard, most likely fertilization occurred a little earlier or later than the fourteenth day of the cycle. Accordingly, the actual gestational age will be slightly different than when calculated by the date of the last menstruation.
For example, if the average cycle duration is not twenty-eight, but thirty-five days, then conception can occur only on the twenty-first day of the cycle, and not on the fourteenth. Accordingly, in the first week of the delay, the real period will be the third week, and by the date of the last menstruation it will be already the sixth week.
When trying to correctly calculate the duration of pregnancy, you should not focus solely on the date of intercourse. As practice shows, sperm cells can remain active in the female genital tract for up to five days, waiting for the maturation of the egg and the completion of fertilization.
How else can you determine the deadline?
In the very first weeks after conception, for the most accurate determination of the gestational age, you can take an analysis for hCG. The results obtained will make it possible to determine the most accurate age of the fetus.
To determine the term at a later stage of gestation, you can sign up for an ultrasound scan. Until the twelfth week of gestation, such a study extremely accurately shows the age of the baby, since its development occurs approximately the same in all women. In this case, the doctor can write as a result both the true (real) age of the fetus and the obstetric gestational age. Accordingly, it is imperative to check with the specialist conducting the research what exactly he means.
How is the gestational age determined during a routine gynecological examination?
A qualified gynecologist, conducting a vaginal examination of a patient, can detect pregnancy at the earliest stages of development, from about the third to fourth week. But of course, the terms he named cannot be called 100% accurate.
How does the duration of the cycle affect the overall duration of pregnancy?
In fact, it makes no difference how long your monthly cycle lasts. On average, about nine months pass from the onset of conception to the date of birth, but this period may deviate in one direction or another, depending on the individual characteristics of the woman, as well as on her from the course of a particular pregnancy.
Conclusion
We talked with you about the difference between real and obstetric pregnancy. Correct determination of the gestational age, taking into account the length of the cycle and the approximate timing of ovulation, helps to calculate the approximate date of birth as accurately as possible. That is why it is extremely important to inform your doctor about all the features of your body.
It is generally accepted that during the normal course of pregnancy, its duration on average in the population is about 280 days if you count from the first day of the last menstrual period what got the name "Obstetric gestational age"... Such a calculation is aimed at determining the timing of prenatal leave and the expected date of delivery, as well as assessing the size of the fetus according to ultrasound data during pregnancy over 12 weeks.
To determine the expected due date, according to the obstetric term, from the date of the first day of the last menstrual period according to the calendar count back three months and add 7 days... However, it should be borne in mind that the estimated due date is not a fixed date. This is just a certain period of time, which is ± 10-12 days, when labor is most likely to occur... The fact is that the gestation period for each woman in each of her pregnancies is strictly individual, varying within certain limits around an average duration of 280 days.
Sometimes they use the calculation of the so-called "Embryonic term" pregnancy from the moment of conception, which is often almost coincides with the date of ovulation... The fact is that a woman's menstrual cycle (the period from the 1st day of one menstruation to the 1st day of the next menstruation) lasts on average 28-30 days. During the first half of the menstrual cycle, a follicle matures in one of the ovaries, and ovulation occurs on days 14-15. In this case, a mature egg comes out of the follicle. Taking into account that a mature egg is capable of fertilization within 2 days after ovulation, and sperm have fertilizing activity within 4 days after ejaculation, the total period of the most probable possibility of conception is about 6 days. The embryonic term turns out to be shorter than obstetric by about 14 - 15 days .
In clinical practice, doctors mainly use the calculation of the "obstetric period", since most pregnant women know well when the first day of the last menstruation was, but not all of them have a clear idea of the date of conception.
It is also possible to determine the duration of pregnancy by the size of the uterus and by the movement of the fetus. However, these criteria are not precise, since they are highly individualized. The fact is that the size of the uterus at the same gestational age in different women varies within a fairly wide range, which does not allow to estimate the gestational age of each particular patient with an accuracy of up to a week.
The sensation of fetal movement is also very subjective, and depends on the sensitivity threshold of each woman. So some women may, for example, begin to feel fetal movements from 18 weeks, while others only from 22 weeks. But in fact, the fetus begins to move from 7-8 weeks.
Quite typical and widespread is the misconception that ultrasound (ultrasound) determines the gestational age... This is not actually happening. In the process of this study, another equally important question is solved - for what period of pregnancy the sizes of the fetus obtained during the study are characteristic, provided that the estimated gestational age is known, which, in turn, is calculated from the first day of the last menstruation or from the date of conception. Therefore, if in some observation, for example, it is known that the expected gestational age is 32 weeks, and according to the ultrasound data, the size of the fetus is typical for a gestational age of 29 weeks, then no one will argue that the gestational age is 29 weeks, and not 32. Will be it was concluded that there is a lag in the size of the fetus by 3 weeks, which will require a more in-depth examination to find out the reasons. In addition, in the dynamics of ultrasound, the rate (growth rate of the fetus) is assessed in accordance with the gestational age.
In the normal course of pregnancy, which occurs in most patients, the size of the fetus and the gestational age are the same, which creates the false assumption that ultrasound can determine the duration of pregnancy.
It is also important to take into account the following circumstances: up to 12 weeks of pregnancy, when the length of the embryo (its coccygeal-parietal size - CTE) and the average inner diameter of the ovum are estimated using ultrasound, the compliance of the measurement results with the gestational age is assessed according to tables calculated for the "embryonic period ", Which is 2 weeks less than obstetric.
At a later date, to compare the results of fetal measurements using ultrasound, use tables designed for obstetric term(from the first day of the last menstruation).
If the doctor who conducted the study before 12 weeks did not make an amendment for 2 weeks for the obstetric period, then there may be disagreements of 2 weeks between the periods of pregnancy, which were assumed according to ultrasound data before 12 weeks and after. In fact, there is no difference. You should only add 2 weeks to the result obtained up to 12 weeks, if this has not been done.
Thus, the gestational age in weeks is determined only on the basis of a set of data, including the date of the last menstruation, the date of conception, the results of ultrasound in dynamics, data on the growth rate of the fetus.
Only after learning about her "interesting" position, each girl begins to calculate gestational age.
In rare situations, a woman herself knows for sure the day of conception, but for this you need to have rather rare sexual relations and even this does not give a 100% guarantee of an accurate determination of the term.
A sperm that has entered the female body is capable of fertilization within a few days, as well as the ovum, therefore, knowing the date of sexual intercourse for sure cannot be said with certainty that fertilization took place on that day. It could have happened later.
And if sexual intercourse is frequent, then the term has to be calculated using other methods.
So, what do you need to know for this.
There are 2 stages of pregnancy - obstetric and embryonic.
This is very confusing for newly minted pregnant women. Let's make a reservation right away that all tables, all sizes, all standards are calculated and described. ONLY taking into account the obstetric term. For this reason, once calculating the obstetric term, forget about the embryonic term, all doctors use only the obstetric term.
This should be taken into account when registering with a antenatal clinic and when conducting analyzes.
Recall that it is very desirable to register with the LCD before 12 obstetric weeks.
The obstetric period is determined by doctors on the first day of the last menstruation before pregnancy.
The embryonic term is the term of conception, it usually lags behind obstetric by about 2 weeks (i.e., obstetric time, for example, 26 weeks, and fetal 24 weeks).
The same, rather specifying terms are:
terms for ultrasound (determined based on the size of the fetus),
period in terms of the size of the uterus (after 12-14 weeks, the height of the fundus of the uterus corresponds to the period, i.e. at 15 weeks, the height of the fundus of the uterus is 14-16 cm),
the term for the level of hCG (informative in the first 12 weeks) and the term for the first movement of the child (primiparas feel the first movements at about 18-20 weeks, multiparous at 16-18).
How to calculate the obstetric gestational age?
According to the obstetric period, pregnancy lasts 40 weeks (280 days), that is, 10 lunar months with 28 days.
The embryonic gestation period is 38 weeks with the number of days in a month 30-31.
It should be borne in mind that the timing of 40 weeks and 38 embryonic is the average duration of pregnancy, because a child can be born earlier or later by 1-2 weeks and this is normal.
This method of calculating the gestational age is the most generally accepted and used for a long time.
For an accurate calculation of the obstetric period, you need to add 280 days to the first day of your last menstruation. You can calculate it in another way: we take the first day of menstruation, subtract 3 months and add 7 days.
Let's look at an example:
1) We subtract 3 months - we get January (4-3 = 1)
2) Now let's calculate the date of birth by obstetric time: April 1 + 7 = 8th, in the end we get that you will give birth on January 8, 2012.
Of course, it is unlikely that on the first day of the last menstruation you were already pregnant, they are guided by this period because it was at this moment that your egg cell began to ripen, which in the future will be fertilized and turn into your baby.
Similarly, the approximate date of pregnancy is calculated, later deadline specified by ultrasound. The most accurate gestational age can be determined by ultrasound up to 12 weeks.
However, often the obstetric, embryonic and ultrasound terms differ. The embryonic one is almost always less than 2 weeks obstetric, but the ultrasound period depends on many factors and is more genetically determined, because it is determined by the size of the fetus, and the fetus can be both large and, vice versa, small.
It is also difficult to determine the timing in women with a cycle length of less than or more than 28 days and irregular periods. In such situations, doctors are guided by the size of the uterus and the results of an ultrasound scan.
In rare cases, this method of determining the obstetric period fails even in women with a regular 28-day cycle, because it all depends on the date of ovulation. Sometimes malfunctions occur in the body and ovulation does not occur in the middle of the cycle, but sooner or later, and it may happen 2 times per cycle.
Exact definition of the term for you!