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How embryonic weeks are counted. If the term, calculated according to the ultrasound scan data, exceeds the obstetric…. What is Obstetric Pregnancy Week

Pregnancy is the most enjoyable event in the life of any woman. Have you noticed how a young lady flourishes during this period? She becomes brighter, more sincere and open. Waiting for a miracle, a woman can worry and worry, which is quite normal and is due to hormonal changes in her body. One of the reasons for concern is worries about the timing of pregnancy. Today we will try to figure out what is the difference between obstetric weeks and ordinary weeks.

Obstetric weeks and regular weeks

When calculating the gestational age, the concepts of obstetric week and obstetric month are used. The obstetric week, like the usual one, consists of seven days. The midwife month consists of four weeks.

How are obstetric weeks calculated?

To determine the date of birth, several methods of calculating the gestational age are used. Among them, there are embryonic, obstetric terms and the term, which is established according to the data of ultrasound examination of the uterus. A normal pregnancy lasts nine months. This is the embryonic period, which is thirty-six weeks from the moment of conception or nine obstetric months. In obstetric practice, the concept of "obstetric weeks" is also used. Few people know about this, so it will be useful to clarify what the obstetric gestational age is and how it can be calculated.

Obstetric weeks of pregnancy are normally forty weeks, which equals two hundred and eighty days or ten months, with one month being twenty-eight days. To calculate the gestational age, add one week to nine months and you will get an approximate due date. Obstetric weeks are counted from the first day of the last menstrual period to the onset of pregnancy. This method of counting has long been used by our ancestors. Normally, every girl and woman has a period once a month, which lasts for 3-5 days. If menstruation occurs regularly, the woman knows she is not pregnant. Obstetric weeks can be calculated only in those women who have already established a menstrual cycle, and menstruation begins at regular intervals.

TheDifference.ru determined that the difference between obstetric weeks and normal weeks is as follows:

  1. The obstetric week is used to calculate the gestational age, the usual week is used to calculate the calendar dates.
  2. Four obstetric weeks are equal to an obstetric month. With calendar weeks, the situation is completely different - here each month does not have a certain number of weeks.

A desired pregnancy is the most exciting and joyful event in the life of an expectant mother. Seeing two red stripes on the test, or suspecting a sudden pregnancy, surely every woman is eagerly eager to get an appointment with an antenatal clinic and hear her pregnancy period. When visiting a specialist, the expectant mother will be sure to be told what period in weeks has already come, and what tests and studies she will need to undergo in the future. But what if the announced deadline does not agree with your personal calculations? How to understand a doctor correctly? But we will now analyze this in detail.

First of all, we note that there are several concepts of the timing of pregnancy. These include:

  • Obstetric
  • Fetal (actual)
  • Term for ultrasound diagnostics.

Now let's take a closer look at each of these concepts.

Obstetric.

It is this gestational age in weeks that the expectant mother is voiced by the obstetrician-gynecologist. According to the same calculated period, he will guide the expectant mother until the end of her pregnancy, make various appointments and conduct a variety of examinations. Obstetricians even have special universal calendars, cheat sheets, by which they very quickly calculate the date of future birth, starting from the set obstetric term.

This gestational age is not considered from the very moment of the actual fertilization of the egg (conception of the child), but from the first day when the last menstruation was, and this is important to remember and understand. But from the first day of the last menstruation to the actual conception, approximately two weeks have already passed (therefore, the medical and actual dates do not usually coincide by two weeks). This happens because somewhere in about two weeks from the beginning of each menstruation, the ovulatory phase is established, that is, just the very moment when conception in a woman is most possible. In general, the time of ovulation falls in the middle of the monthly cycle, for example, if your cycle is 28 days, then ovulation will most likely happen on the 14th day. Therefore, in the obstetric calculation of pregnancy, there is always about two weeks, when, in fact, conception has not yet occurred. The question arises, why, then, the doctor determines not the actual time, but his own, the doctor's? And the thing is that obstetricians all over the world are guided by this period due to several factors. A woman, having come to an appointment, cannot always say with accuracy when she had an intimacy, and even if she does, it does not at all guarantee that the sperm fertilized the egg on that very day. Further, the duration of the menstrual cycle is always individual for each woman. Someone may have 25 days, someone 33, but for someone it is far from constant. And therefore, in order not to understand each individual case, and not to calculate the date of ovulation, such a universal system was created that is suitable for all women to determine the obstetric term.

Embryonic (actual).

This is exactly the same period that describes the actual pregnancy that has already occurred, the conception that has occurred. Knowing the obstetric term, each expectant mother will be able to easily calculate her actual one herself, simply by reducing the first by about two weeks. For a more accurate calculation, a woman still needs to know how many days her menstrual cycle lasts, and when ovulation occurs. As soon as the expectant mother begins to suspect that the fact of pregnancy has come, she just needs to calculate when the ovulatory period was, that is, somewhere in a couple of weeks from the last menstruation. This time will be the estimated days of the baby's conception.

Pregnancy period by ultrasound.

It should be noted that ultrasound diagnostics is also considered one of the most reliable methods for determining the duration of pregnancy. In most cases, this method is only additional to the previously set deadlines, and is prescribed for the purpose of monitoring the development and growth of the fetus. But it can also become the main method, in such cases as irregular periods with different duration of the menstrual cycle, or repeated pregnancy immediately after the first birth, when the mother, by giving up breastfeeding, restores the ability to mature the egg.

When determining the duration of pregnancy by ultrasound diagnostics, you need to take into account the period (trimester) when the study took place. If it was done at the very beginning, in the first trimester, then the main indicator on which the doctor relies is the size of the ovum and the coccygeal-parietal size. Focusing on the results obtained, the ultrasound doctor analyzes them with average indicators, and gives an opinion on the duration of pregnancy.

From the next trimesters, conducting such studies, the specialist measures the circumference of the head, tummy, thigh length, overall fetal growth, and other important indicators, by which he draws a conclusion about the gestational age.

How to calculate the date of future birth yourself

It is not at all difficult to calculate the date of birth of a future baby, especially since there are several universal formulas for this:

  1. Last day of expired periods + 9 months + 7 days. An illustrative example: The date of the last day of menstruation is March 15th. We add 9 months, we get December 15. We add another 7 days, it turns out December 22.
  2. There is another method: The last day of the past period is 3 months + 7 days. The same illustrative example, only we count differently: The date of the last day of menstruation is March 15th. We subtract 3 months, it comes out on December 15th. We add 7 days, the result is December 22.

Well, and as an afterword, I would like to note that no matter what date of birth the doctors or the expectant mother herself calculate, you always need to remember that delivery on time is the period between 38 and 42 weeks. After all, every woman has her own individual organism, just like every future baby has her own special development program, which is laid down only by nature, and therefore only the baby knows when it is best for him to be born.

Modern experts use generally accepted norms regarding the bearing of a woman's fetus. Pregnancy without complications lasts an average of 280 days. Usually, the very beginning of the term means the first day of the last menstrual bleeding. This counting system is called obstetric timing. In modern gynecology, according to such data, the time of prenatal leave is calculated, the size of the fetus is estimated by ultrasound, and the estimated date of birth is calculated.

What is Obstetric Pregnancy Week?

The specialist, in order to determine the time of delivery by the obstetric method, counts exactly three months back from the initial day of the last menstrual bleeding, then adds 7 days to the result. It should be borne in mind that the resulting date of birth is not an exact day, but a certain range that can recede 10-12 days forward or backward from the most likely day of the natural birth of the fetus. Each pregnancy follows a unique scenario, so the time for carrying a baby varies. It is noticed that specialists mainly operate with the concept of obstetric term, because almost every unexpectedly pregnant woman can name the date of the last menstruation, since it is customary to record these data in the calendar, but few will be able to accurately indicate the day when conception occurred.

A feature of the obstetric period of pregnancy is that it contains the full cycle of the birth of a new life, that is, the time from the beginning of the life of the egg, and until the appearance of a fully developed and ready-to-live child in the external world. There is nothing complicated in how obstetric weeks of pregnancy are counted. The week itself, as usual, is 7 days. The difference was found to be hidden in the number of months. We know that the gestation period is 9 calendar months, which is equal to 10 obstetric months, which is an average of 40 weeks - if you count from the date of your last period, and 38 weeks - if you start from the date of conception.

Obstetric gestational age: exceeds the embryonic term by 14-15 days

Determining the duration of pregnancy

What is embryonic gestation?

It is known that in medical practice, the embryonic gestation period is also calculated, which begins with the fact of conception and, as a rule, coincides with the time of ovulation. A woman's menstrual cycle, lasting from the first day of her period until the first day of her next period, is usually within 28-30 days. During the first part of the cycle, the follicle matures inside the ovary, by the 14-15th day, the ovulation process is observed, implying the release of the formed egg from the follicle. It has been scientifically proven that after ovulation for about 2 more days, the egg retains the ability to fully further develop through fertilization. It is also taken into account that the sperm produced by a man are viable and prone to fertilization for about 4 days. It turns out that only 6 days have the highest probability of conception. Based on the foregoing, a feature of the obstetric term can be distinguished: it certainly exceeds the embryonic one. The difference between these concepts is 14-15 days.

Calculation of gestational age according to ultrasound

It is theoretically possible to calculate the gestational age based on the size of the uterus and the nature of fetal movements. These criteria cannot be considered accurate, because these are strictly individual data with a significant scatter. In fact, the fetus begins to move at 7-8 weeks of life, but the mother may feel tremors at 18-20 weeks. Every woman needs to have an idea of ​​ovulation and fetal timing, monitor her own menstrual cycle, and at least in general terms know how obstetric weeks of pregnancy are counted. Having accurate data will facilitate medical follow-up and increase the chances of a normal delivery of a healthy baby.

Today, many unenlightened people mistakenly believe that pregnancy can be determined by performing an ultrasound scan. In reality, this is not the case. The main task of ultrasound is to assess the state of the embryo. Experts are trying to find out with what gestational age the real size of the fetus is comparable, based on the estimated period, calculated directly from conception or the beginning of the last menstrual bleeding. Ultrasound is prescribed at least 3 times to assess the dynamics of development and growth of the fetus in accordance with the gestational age.

For example, it was previously found that the period is 32 weeks, and the ultrasound examination showed such sizes of the fetus, which are inherent only in a 29-week-old embryo. In this case, doctors will not adjust the period according to the size, but conclude that there is a developmental delay of 3 weeks, and this implies a detailed examination and determination of the cause of the deviations.

In many cases, the pregnancy is proceeding normally, and an ultrasound scan reveals the correspondence between the size of the fetus's body and the established period. This fact gives rise to a false statement that an ultrasound examination is a way to determine the duration of pregnancy.

Based on the above information, we can conclude that it is really important for expectant mothers to know how obstetric weeks of pregnancy are counted. Experts emphasize that the correct gestational age in weeks can be established by examining the totality of data, which includes the following indicators: fetal growth dynamics, the onset of the last menstrual bleeding, the results of several ultrasound examinations and the date of conception.

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More accurate data will be told to you by the doctor, having inquired at the beginning of the day of the beginning of the last menstruation. But his findings may confuse you. So still - how to calculate the obstetric gestational age and delivery time?

Various counting methods

There are two ways in which the gestational age is determined:

  • embryonic - from the day of fertilization of the egg;
  • obstetric - from the day the last menstruation began.

The second method may seem unusual for a woman, because she, as a rule, focuses on the period of ovulation and sexual intercourse. But recently, obstetricians-gynecologists operate on them.

Calculation example

To understand how obstetric pregnancy is determined , and how it differs from embryonic, consider an example. If a woman has a regular 26-day cycle, then the obstetric period will be determined based on the first day of the last menstruation.

Conception, as a rule, occurs during ovulation, which means in the middle of the cycle - this is the beginning of the embryonic period. Then the difference between the two methods of counting will be 13 days.

Special cases

But with hormonal disorders, taking certain medications, emotional shocks, ovulation can occur on a completely different day of the cycle. Then the data will be distorted.

The last menstruation can also be before a previous pregnancy, if it occurred during lactational amenorrhea. This happens quite often, especially when the feeding is reduced. In this case, the time of the onset of menstruation is not informative.

What will ultrasound show?

The most accurate indicator will be if an ultrasound scan is performed before 12 weeks, when the fetus does not differ from woman to woman. The doctor evaluates the size of the ovum, the coccygeal-parietal size and records the result, comparing it with the average.

After the first trimester, babies may differ - one baby is longer, the other is smaller. This makes the indicators inaccurate, but in general, the ultrasound data will coincide with the obstetric period.

The fact is that the tables of indicators by which the doctor evaluates the fetus have already been adjusted for this method.

Only ultrasound data up to 6 weeks can coincide with the embryonic period, but such early studies are not recommended.

Why gynecologists use the term "obstetric"

This technique has been used since the days when there were no such devices as ultrasound. The only observation that helped establish the fact of conception was the cessation of menstruation.

In modern practice, the objective reasons for using this method:

  • Every woman's menstrual cycle is different in length, and for some, it is irregular. It is difficult to calculate the day of ovulation for each case, it is easier to find out the date of the last menstruation.
  • It is impossible to know the exact date of fertilization for two reasons. First, you may not remember the day of sexual intercourse. Secondly, conception may not occur on the same day, but later.

It is possible to establish the date more accurately only with the help of ultrasound and other signs, such as the size of the uterus.

When will the baby be born?

A woman is not particularly worried about the medical nuances of calculations, but she wants to know when the baby is due. How do you know your obstetric gestational age? Take the start date of your last period and add 40 weeks or 280 days.