How many months a pregnancy lasts is a question many expectant mothers are interested in. There is no way to determine the obstetrical term with maximum accuracy, all predictions have a certain probability of error. The birth may be premature, late or on time – regardless of this, you should stick to the recommendations prescribed by your doctor. There are several ways to determine the length of your pregnancy.
It is impossible to tell exactly how many months a pregnancy will last. Doctors confirm that the term of carrying a child is 9 months or three trimesters, which is a kind of norm. Even when the expectant mother goes to the doctor for the first time, the approximate due date is determined. Soon, this date is adjusted on the basis of tests and ultrasound.
Exactly 40 weeks is the duration of pregnancy in the absence of any abnormalities. It is nine calendar months or ten obstetric months. In general, the term of carrying a baby is 280 days. Timely delivery occurs from the 37th to the 42nd week. Preterm births are considered to be those that began before the 37th week, after the 42nd week – late births. That is, they are considered deviations from the norm.
The duration of pregnancy conventionally consists of two periods: embryonic and fetal. The embryonic period from the time of fertilization lasts until the tenth week (obstetric term is considered). At this point, the fetus is formed and develops in the body of the expectant mother. This includes the formation of tissues, organs, and the placenta.
The fetal period lasts from 11 weeks of gestational age until delivery. During this time, you can notice active growth of the fetus, changes in its proportions, and the development of all organ systems. In addition, the first tremors of the fetus become noticeable.
The duration of pregnancy depends on several factors:
Analyzing all the above data, doctors calculate the duration of pregnancy. It can be determined by days and weeks. This confirms that for each expectant mother, the terms are set individually.
The obstetric term can not always be accurate. Therefore, preterm birth is considered premature if it begins before the 37th week. The baby in this case is recognized as premature – in this case it needs to stay in a medical facility under the care of specialists for some more time.
The degree of prematurity of the baby is determined by the following scale;
40 weeks – this is the length of pregnancy is considered “normal”. There are several reasons for giving birth earlier than the appointed term:
| Symptoms | Signs |
| Rupture of fetal membranes ahead of schedule | Frequency of contractions more than 8 times per hour |
| Chorioamnionitis or other intrauterine infections | Mild blunt back pain |
| Multiple pregnancy | Pelvic pelvic thrust with aching sensation that increases at night |
| Fetal or placental abnormalities | Diarrhea |
| Uterine abnormalities | A bloody vaginal discharge |
| Pyelonephritis | Watery vaginal discharge |
Quite often, it is very difficult to determine why labor started before the recommended duration of pregnancy. It is only worth remembering that a premature birth always carries a risk not only to the woman in labor, but also to her baby. So, giving birth earlier than planned, can lead to intraventricular hemorrhage or impaired neuropsychiatric development.
Delayed labor that lasts longer than the normal duration of the pregnancy is considered abnormal. Thus, delayed labor occurs when it begins later than the determinate 40 weeks. This also carries certain deadlines for the fetus: it feels trophic and oxygen deprivation. Prematurity at several weeks is determined by varying degrees of severity.
The average duration of pregnancy that is considered to be pre-term is 280 days. It is counted from the 1st day of the last menstrual period. When calculating the duration of pregnancy, the length of the menstrual cycle also plays a role.
The incidence of late delivery is 10-12%. The risk increases if the pregnant woman has neuroendocrine disorders or CNS malformations. The duration of pregnancy is quite often prolonged in first-born and multiple-born women.
Increased duration of pregnancy leads to severe complications for the fetus and the mother. Given that the fetus becomes larger in size and the central nervous system has greater maturity, this always leads to birth trauma.
It is possible to determine the duration of pregnancy most accurately after ultrasound tests. With modern equipment, it is possible to determine the gestational age of the unborn child. In addition, you can determine the duration of pregnancy using the following technique: add 266 days to the day of the beginning of the last menstruation. It is worth remembering that the date obtained is only approximate. If the baby appears at any time after 37 weeks, it is already considered normal.
It is possible to determine the duration of pregnancy using different methods. Regardless of the method chosen, it is necessary to focus on the following factors:
Even after determining the approximate due date, it is worth remembering that the main task of the expectant mother remains calm anticipation and love for the future baby. To avoid unforeseen developments, you should regularly consult with your doctor, adhere to all established recommendations, undergo tests and avoid stressful situations.
This method of calculating the duration of pregnancy is one of the most common. You can use it only if your cycle is regular and has the same interval.
For example, if the cycle lasts on average about 35 days (for comparison, many women have a cycle of 26-28 days), then with the greatest probability of conception will occur on day 21 of the cycle, and not on day 14, as with a cycle of 28 days. Thus, the calculated term according to this methodology will be one week longer than the real obstetric duration of pregnancy.
You can get an obstetric due date by adding two weeks to the known date of conception. Even if a woman knows the exact date of ovulation or the date of intercourse that led to conception, it does not mean that she knows the date of conception with absolute certainty. The fact is that the sperm can lead to conception for another 5 days, sometimes even longer, after entering a woman’s body.
Meanwhile, the mature egg can be fertilized for 2 days after ovulation. At this time, it is still capable of conception. Because of this, you can not be guided by the exact date of intercourse or ovulation. After all, there is no exact guarantee that conception occurred on that particular day. The actual date of conception can be earlier or later. Therefore, the duration of pregnancy determined by this method can not be considered absolutely accurate.
A slightly different principle is used to calculate the duration of pregnancy if it occurred as a result of IVF. In this case, the fertilization of the egg sperm is responsible for the embryologist. Development of embryos in the laboratory lasts for 3-5 days, and then they are transferred to the uterus.
Doctors calculate the true duration of pregnancy after IVF from the date when the ovarian puncture was performed. This is one of the stages of the procedure, when the follicular fluid is taken and fertilization takes place. Two weeks are added from the date of the ovarian puncture to determine the obstetric term.
If the embryo was frozen in liquid nitrogen (this process is called cryopreservation) before being transferred into the uterus, you can only determine the exact duration of pregnancy by adding 5 days to the transfer date. To know the obstetric term, add 14 days to the obtained true duration.
When examining a woman in a gynecological chair, the doctor determines the size of the uterus with both hands. This also helps determine the approximate duration of pregnancy. This method of determination demonstrates the greatest accuracy in the early stages of pregnancy – up to about 12 weeks. The earliest term that can be determined from the size of the uterus is 5 weeks.
By this time there is a slight increase in the uterus, as well as its softening. It takes on a more round shape. At later terms, the size of the uterus may vary depending on the size of the fetus, the amount of amniotic fluid, and the pelvic structure of the expectant mother. For example, it is accepted that at 16 weeks (4 months), the bottom of the uterus is located at the middle of the distance between the pubis and the navel, at 24 weeks (6 months), the bottom of the uterus is already displaced to the level of the navel.
In the early term, you can determine with the greatest accuracy the duration of pregnancy. To do this, an ultrasound is performed, during which the size of the fetus egg and embryo are measured. In the first trimester a small “black circle” is determined – this is the fetal egg, followed by the emergence of the embryo. Already towards the end of the first trimester, this embryo will look like a small “band”. Also in this term its heartbeat becomes distinguishable.
More accurate is the gestational age calculated by measuring the embryo’s CRL. After 12 weeks, the term of pregnancy by ultrasound is determined by taking into account the so-called fetometry. Thus, when determining how many months the pregnancy will last, various fetal sizes are taken into account – from the length of the arms to the head.
Until the second trimester, there is proportional growth of the embryo. With this in mind, its size will be approximately identical in all women with the same gestational age. Later on, fetal sizes will vary among expectant mothers. This is absolutely normal, as it is influenced by very many factors, ranging from the weight of the mother to the age of the father of the child. In this case it is no longer possible to determine the exact duration of pregnancy with an ultrasound scan.
If at a long term becomes noticeable lag in the size of the fetus, most often, doctors regard this as a developmental disorder. It is usually due to the fact that the placenta does not fully transport oxygen and nutrients.
HCG is a hormone that the placenta secretes during all months of carrying the baby. It is the first hormone that signals the successful conception of the baby. Its amount gradually increases up to the 11th week, and then begins to decline gradually. In the first months, determination of hCG concentration in blood helps determine the duration of pregnancy with accuracy.
Once the tests are obtained, you should keep in mind that the lab tests for the hormone level corresponds to the due date of delivery, which is usually the fetal period. To determine the usual obstetric duration of pregnancy, you need to add 14 weeks to the date obtained.
Recently, urine tests to determine the duration of pregnancy are becoming particularly popular. Their principle is aimed at determining the concentration of a hormone in the urine of a pregnant woman. It is worth remembering that with the help of this test is the definition of the fetal period.
This method of determining the term shows the least accurate results, so it is used quite rarely. It is based on the belief that women who give birth for the first time, begin to feel the first stirring of the baby around 20 weeks, and second-born women earlier – at 18 weeks. That is why many obstetricians and gynecologists recommend remembering exactly when the fetus first moved and entering this data in the exchange card.
This method of determining the duration of pregnancy often shows error. Indeed, women who are expecting a baby for the first time begin to feel fetal movements later than women who already have children. This is due only to the experience of women who can already easily identify the movement of the baby and know what sensations it is accompanied by.
Quite often, women compare the first movements of the fetus with a feeling of fluid overflow in the stomach. As a rule, the first movements are rare and irregular. Moreover, the sensitivity of the woman in labor plays a very important role here.
There is another nuance: slim women begin to feel the stirring faster compared to women with excess weight. If a woman in labor leads an active life and works a lot, she will feel the stirring much later. Once the due date has been determined, your doctor can calculate the approximate length of pregnancy. On average, the obstetric term is 280 days or 40 weeks.
In order to carry a baby without complications, it is necessary to adhere to certain recommendations:
If premature birth has previously occurred or if risk factors appear, the doctor may prescribe a course of progesterone injections – this will normalize the condition of the expectant mother and her baby. Thus, the normal duration of carrying a baby is 40 weeks. There are several factors that can be used to determine if the delivery is premature or delayed. There are also several techniques that are actively used in calculating the due date of the baby.
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