In multiparous women, there is usually no difficulty in calculating the gestational age. But women who have become pregnant for the first time, for the most part, are faced with a situation when their calculations do not coincide with the doctor's, and this is often interpreted as a mistake of obstetricians. Let's learn how to correctly count the weeks of pregnancy.
Counting methods
Counting the weeks of pregnancy is very important both for the expectant mother and for doctors, primarily because it allows you to track the development of the baby and the progression of pregnancy, comparing them with general standards. Also, determining the exact date will help calculate the day on which the birth is expected to occur. All examinations, analyzes, screenings, all tables of norms of analyzes and ultrasound data in gynecology and obstetrics are compiled in obstetric weeks, which usually differ significantly from the actual ones.
So that there are no discrepancies and confusion, a woman is recommended from the very beginning to get used to counting the term as doctors do.
It is difficult to say whether the date will be exact. Most likely not, because the obstetric method is an average, but it is he who is the most optimal. There are no exact methods because it is impossible to find out the time of conception even with an accuracy of the day... A woman is only fertile for 24-36 hours throughout her cycle. This is the period of her ovulation. This is how much the mature egg retains its viability. Spermatozoa may already be in the genital tract by the time the oocyte leaves the follicle, or they can reach the egg later, but again no later than a day after its release. If the conditions are met, conception occurs.
Ovulation in the vast majority of women occurs in the middle of the cycle, at about 14 days in a 28-day cycle. But it may well shift and occur later, stress, medication, fatigue, colds and a host of other factors can affect this, which in principle cannot be fully taken into account.
Thus, a woman who claims to know exactly when the baby was conceived may be delusional. If a lady leads a normal saturated sex life, then in principle she cannot know the exact moment of conception... Gynecologists, despite all the development of modern medicine, also cannot establish the day and hour of conception, and therefore use a more simplified system of calculating obstetric weeks, unified for all.
Default the first day of the first week of pregnancy is the first day of the cycle in which a significant event took place - the conception of a baby... That is, the lady is having her period, and the first week of pregnancy is already underway. That is why any visit to a doctor while carrying a baby begins with a simple question about the date of the last menstruation - this is how the dates are checked.
Also you can calculate pregnancy according to ultrasound data, but this is a less accurate method, because the size of the fetus can, for various reasons, be more or less than the norm for the same period in different women.
Let's walk through the basic methods step by step.
Obstetric calendar
It is this method that is considered the most correct, despite the fact that it causes genuine bewilderment among inexperienced pregnant women - is it possible to be pregnant when there has not yet been sexual intercourse? Can. The first two weeks of the obstetric period is the first part of the menstrual cycle, preceding ovulation, the second two weeks - the pregnancy is already actual, but not yet obvious. Only at the end of the 4th week of pregnancy there is a delay when tests can be done, take blood tests for hCG. If they are positive, the doctor makes an appropriate decision based on the date of the last menstrual period - 4 weeks of pregnancy. In fact, from the moment the baby began to exist, it takes about 2 weeks to this moment. Development weeks are called embryonic, and it is not accepted to count the gestational age in them.
Obstetric weeks in pregnancy are 40 or more. The due date falls at the end of week 40. But labor can occur at any time from the full 37 to 42 weeks, and this will be considered the absolute norm.
Pregnancy began to be considered obstetric weeks long before ultrasound was invented by mankind, and certainly there were no online counters and calculators.
There are several ways to calculate the date of birth (only an estimated, approximate) according to obstetric techniques:
- (first day of menstruation minus three months) + 7 days;
- (first day of menstruation + 9 months) + 7 days;
- first day of menstruation plus 280 days.
Which one to use, the doctor will decide on his own. And he will do this when registering with the antenatal clinic, when the expectant mother turns there.
One obstetric month is equal to four obstetric weeks, in pregnancy there are exactly 10 obstetric months, divided into three trimesters. The period from the moment of conception is about two weeks less than obstetric, and now we know why this is exactly the case.
If the doctor, after examining a woman, twisting the calendar in her hands and thinking, says that she is already 8 weeks pregnant, this is not a mistake, but literally the following: 8 obstetric weeks = 6 weeks from the moment of conception = exactly 4 weeks from the start of the delay.
Ultrasonic method
Ultrasound machines are programmed for obstetric weeks, and therefore if the ultrasound shows that the gestation period is 7 weeks, this means that the pregnancy is exactly 7 weeks, and not 9, as some think, given that two obstetric weeks need to be added to the actual period. 7 weeks by ultrasound = 5 weeks of embryonic development and nothing else.
Modern ultrasound scanners give results in weeks and days, that is, 7 weeks and 5 days or 7 weeks and 3 days, which allows you to clarify the gestational age already calculated by obstetricians.
The ultrasound method for determining the exact period is relevant for women who do not remember the date of the start of the last menstruation, who do not know it due to the irregularity of the cycle, the broken cycle, as well as after a successful IVF protocol.
It is only important to know that it is possible to establish the most accurately the term for an ultrasound examination only in the early stages. This is due to the fact that all embryos during embryogenesis (up to 9-10 weeks of obstetric time) grow at approximately the same rate.
Then genetic factors, an individual development program come into force: one baby, whose parents are not very tall, is destined to be medium-sized and small in stature, and the other will have impressive growth and weight indicators from the middle of pregnancy.
The deadline on which you can focus on the ultrasound data in determining the timing is 11-13 weeks, it is at this time that the first prenatal screening is carried out, the purpose of which is not only to detect the likelihood of chromosomal abnormalities of the fetus, but also to adjust the timing.
Gestation period
Here is another obstetric term that raises a lot of questions not only among inexperienced expectant mothers who are expecting the birth of their first children, but also among women who have given birth before - how long does gestation begin, what is it, why is it considered at all?
This term hides the embryonic period already familiar to us, that is, the period from the moment of the fusion of the sex cells of the mother and father and the beginning of a new independent child's life. The exact gestational age is known only to those who conceived under the supervision of doctors - who was inseminated on the day of ovulation, confirmed by an ultrasound protocol, who did IVF (in this case, doctors not only up to the day, but also up to an hour know when and how the egg and sperm merged, because it happened in a test tube) ...
This does not mean at all that pregnant women after IVF should consider the term in its gestational equivalent. The gestation period, like others, will be counted in obstetric weeks from the first day of the last menstruation, if the woman knows her, or according to ultrasound data, but again strictly in obstetric weeks.
Online calendars and counters
A modern woman does not need to make calculations for a long time and painfully with a pencil and a calendar, adding or subtracting months to calculate the PDD - the estimated date of birth. Today there are a lot of all kinds of calendars and counters. It is enough to enter the date of the last menstruation and the duration of your menstrual cycle in them., and now the result is already - and the current date, and the estimated day of birth, and the ordinal number of the month, trimester, and even the probability of the birth of a boy or girl (everything except this point is true, the last point - for fun, comes true with a probability of 50 / 50).
Some counters are equipped with detailed functions: they not only count everything, but also provide detailed information about how the baby is developing by weeks, what is its height and weight, and developmental norms. Counters are free.
PDR - for sure or not?
And finally, it should be clarified about the accuracy of the DA. A specific day is indicated, for example, March 15. This does not mean that the woman will give birth on this very day. Little of, strictly in the PDR, no more than 5% of pregnant women give birth - these are the medical statistics. The PDR itself does not exist in order for the future dad to postpone all affairs on this day in advance, and not so that the future mother would check the forecasts of numerologists and saints to choose a name for the one born on that day. PDR is an approximate guideline. The birth itself will occur when both the maternal and the child's organisms are fully prepared for this responsible process..
At 37-38 weeks, up to 20% of children are born, at 38-39 weeks - about 30%, after 39 weeks - 40%, the remaining 10% of babies appear either before 37 weeks or after 40 weeks. Up to 42 weeks inclusive, childbirth is considered urgent, pregnancy has the status of prolonged, but not postponed, as many think. Therefore, feel free to add 2 weeks to the PDR or subtract 2 weeks from it. During the resulting month, the child can be born at any time.
If you have a large fetus or your menstrual cycle usually lasts more than 32 days, then there is every chance that your pregnancy will not be limited to 40 weeks. If you have multiple pregnancies or have a normal menstrual cycle of less than 28 days, the chances are good that you will have labor before 40 weeks.
The following video will show you how to calculate the estimated due date.
