On average, the pregnancy lasts 280 days — these are 40 weeks, or 10 lunar months. The last point deserves special attention, because the duration of the lunar month for each woman will be different, it corresponds to the length of the menstrual cycle. We usually talk about 28–30 days, but there are quite a few exceptions.
If menstruation comes every 24 days, it means that the term of labor will come after 240, not 280 days. And no matter how hard the doctors try to extend such a pregnancy, a woman will still give birth in her time, and, of course, a healthy baby.
Let’s do the calculations!
To determine the duration of pregnancy for a particular day, you can use the calendar. From the 1st day of the last menstruation, you need to count the number of weeks before the selected date.
For example, the 1st day of the last menstruation is 2.03.09. We need to know the gestational age on 12.10.09. We count the weeks on Mondays until 10/12/09.
It turns out that the desired value on the chosen day is 32 weeks. You ask why the starting point was exactly the 1st day of the last menstruation?
The fact is that it is difficult to establish the exact date of conception, therefore a more objective and clear indicator was chosen as a reference point for calculations. And although it is known that conception can occur between the 11th and 17th day of the cycle, this interval still gives room for many options.
The practice of determining the duration of pregnancy on the 1st day of the last menstruation has been with the specialists for a long time. For example, for doctors of ultrasound diagnostics, special tables were compiled based on data on the changes that occur in the future mother’s body with the onset of waiting.
These events and sees the doctor on the monitor screen. But ultrasound data is not the only benchmark when it comes to determining the duration of pregnancy.
The obstetrician will consider a few more reliable indicators.
The results of the 1st examination in the female consultation. From the first weeks of pregnancy, the uterus begins to increase in size, and every centimeter of increase corresponds to a certain week of waiting.
By the way, the earlier a woman goes to the doctor, the more accurately you can set the waiting period.
The term of the first movement of the baby. During the first pregnancy, the woman will feel it at 20 weeks; then at 18 weeks.
True, I must admit that not all future mothers remember this moment.
These ultrasound. The doctor measures the size of the future baby: his head, breasts, tummy, thigh length, degree of development of organs, maturity of the placenta.
Then, as we have said, he compares the information with the tables, where each indicator corresponds to a certain period of pregnancy.
The height of the bottom of the uterus. It is determined after 12 weeks of pregnancy, and its values also indicate a specific waiting time.
Until that time, the uterus will be softened and enlarged: at 6 weeks – the size of a chicken egg, at 8 – with a female fist or goose egg, at 12 – like a male fist.
Date of issuing maternity leave (this is 30 weeks). It is determined by the sum of all the above data, and therefore this milestone is considered to be a very reliable benchmark.
Pregnancy conditionally divided into 3 parts: I three-mestras (from the beginning to 13 weeks); The second trimester (from the 14th to the 26th week); III trimester (from the 27th to the 40th week). This division is associated with the peculiarities of its course in these terms.
- I trimester – a woman’s body is only tuned to pregnancy. Doubtful and probable signs of it (drowsiness, nausea) appear, the uterus grows, but it cannot be determined from the outside.
- II trimester usually proceeds calmly. Expectant mother adapted to pregnancy.
- Term III requires the special attention of obstetricians. Now it is important to prevent complications that appear during this period.
The knowledge of the exact duration of pregnancy is necessary for obstetricians in order to conduct it correctly. For example, with the onset of the 41st week there is reason to fear that the wait is delayed, and the expectant mother should be hospitalized in the maternity hospital in order to understand the situation.
If, according to the ultrasound, it turns out that the placenta is “old”, which means that the baby is not very nourishing and the baby is expected to be large, in order to avoid difficulties during its movement through the mom’s pelvis, it is necessary to speed up the onset of labor and the doctors may decide to do a caesarean section. If the placenta works well and the baby is of normal size – there is no danger, and you can not rush things, preparing the woman for childbirth with the help of estrogens and prostaglandins – the hormones that “turn on” them.
Mistakes in determining the duration of pregnancy mainly occur in relation to expectant mothers, whose cycle is irregular, for example, 40–50 days. After all, calculations based on these figures will be incorrect.
And pregnancy can not last 500−600 days! But in this case it is difficult to determine the duration of the lunar month of the patient; It is not clear at what point in the cycle ovulation could occur (the output of the egg ready for fertilization) and conception.
Fortunately, such miscalculations are quickly corrected due to the already known indicators of pregnancy development: the height of the uterus after 12 weeks; its value at the first examination in the antenatal clinic; time of the first movement of the baby; this ultrasound.
So do not worry: usually the period of pregnancy and childbirth experts determine correctly. The only exception is women who are not observed during pregnancy by a doctor.
The possibility of an error with the calculation of the waiting time and the date of delivery will be higher if the woman also has an irregular cycle. It is possible to correct such a mistake in the maternity hospital if there is an opportunity to make the patient an ultrasound scan.
For the future mother, the forerunners of the onset of labor will be the following events:
- 2 weeks before the decisive day, the bottom of the uterus falls and it becomes easier for the woman to breathe, but it is harder to walk;
- 10–14 days may appear irregular contractions (they are also called false or training);
- about 6 hours before the start of regular contractions, the “mucus plug” departs – a piece of mucus with streaks of blood.
In terms of the term of delivery, the “standard” is considered to be the segment from the 38th to the 40th week of pregnancy. Then they will be called timely. The interval from the 28th to the 37th week will indicate the prematurity of the event, and the period of 41–42 weeks will indicate a delay.
However, at the stage of 41 weeks of waiting, we can talk about both post-term and prolonged pregnancy. The judge in this dispute will be the ultrasound data.
The latter, although it lasts longer than usual, is not accompanied by problems in the work of the placenta and its “aging”, and the baby feels good.
To calculate the estimated time of delivery, you can again take up the calendar. From the first day of the last menstruation, count 40 weeks, and the desired value will be obtained.
You can use the formula: from the date of the first day of the last menstruation – 3 months + 7 days. For example, the first date is 15.04.
We count: IV – III = I; 15 + 7 = 21. The expected birth date is 21.I, that is, January 21st.
The obstetrician leading the pregnancy and the doctor at the maternity hospital will base their calculations on the same formula, taking into account the still familiar survey data (the results of the examination during the first visit to the antenatal clinic, the ultrasound data, the period of the first movements of the baby and the date of maternity leave) . The exact duration of pregnancy is of great importance for obstetricians: depending on it, they will develop the tactics of childbirth.
For example, at 34 weeks for pain in the lower abdomen, therapy will be prescribed to keep the pregnancy; and in the same situation, at the stage of 38–40 weeks, they will only watch how the labor activity goes; for a period of 41–42 weeks and an “aged placenta” (according to an ultrasound scan) – they will hasten to accelerate the development of events to alleviate the condition of the baby.