How many months does pregnancy last — this is a question that interests many expectant mothers. Determining the obstetric term with maximum precision is not possible, as all predictions have a certain probability of error. Births may be premature, overdue, or on time — regardless, it’s important to follow the recommendations prescribed by the doctor. The duration of pregnancy can be determined in several ways.
It is impossible to say exactly how many months the pregnancy will last. Doctors confirm that the duration of carrying a baby is 9 months or three trimesters, which is a kind of standard. During the first visit, the expected due date is determined. Soon after, this date is adjusted based on tests and ultrasound results.
The duration of pregnancy without any deviations is exactly 40 weeks. This is nine calendar months or ten obstetric months. Overall, the duration of carrying a baby is 280 days. Timely delivery occurs from the 37th to the 42nd week. Deliveries that begin before the 37th week are considered premature, and after the 42nd week are considered overdue. These are deemed deviations from the norm.
The duration of pregnancy conditionally consists of two periods: embryonic and fetal. The embryonic period lasts from the moment of fertilization until the tenth week (considered as the obstetric term). During this time, the organism of the future mother forms and develops the fetus. This includes the formation of tissues, organs, and the placenta in the embryo.
The fetal period lasts from the 11th week of the obstetric term until childbirth. During this time, the active growth of the fetus, changes in its proportions, and the development of all organ systems can be observed. Additionally, the first movements become noticeable.
The duration of pregnancy depends on several factors:
By analyzing all the above-mentioned data, doctors calculate the duration of pregnancy. It can be determined by days and weeks. This confirms that for each expectant mother, the timing is set individually.
The obstetric term cannot always be precise. Therefore, childbirth that begins before the 37th week is considered premature. The baby in this case is recognized as premature and requires being in a medical facility under the supervision of specialists for a certain period of time.
The degree of prematurity of the child is determined by the following scale;
40 weeks — this is the duration considered “normal” for a pregnancy. There are several reasons for labor occurring earlier than expected:
| Symptoms | Signs |
| Premature rupture of membranes | Contractions more than 8 times per hour |
| Chorioamnionitis or other intrauterine infections | Dull lower back pain |
| Multiple pregnancy | Pelvic aches intensifying at night |
| Fetal or placental abnormalities | Diarrhea |
| Uterine pathologies | Bloody vaginal discharge |
| Pyelonephritis | Watery vaginal discharge |
Quite often, determining why labor began earlier than the recommended duration of pregnancy is very difficult. It is important to remember that preterm labor always carries risks not only for the mother but also for her child. Thus, giving birth earlier than planned can lead to intraventricular hemorrhage or impairments in neuropsychological development.
Carrying the pregnancy longer than the usual duration is considered a pathology. Overdue labor occurs when it starts after the determined 40 weeks. This also poses certain risks for the fetus: it experiences nutritional and oxygen deprivation. Being overdue by a few weeks is characterized by varying degrees of severity.
The average duration of a pregnancy considered full-term is 280 days. It is counted from the first 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 overdue births is 10-12%. The risk increases if the pregnant woman has neuroendocrine disorders or CNS developmental abnormalities. The duration of pregnancy is quite often extended in first-time mothers and those who have given birth many times.
Lengthening the duration of pregnancy leads to serious complications for both the fetus and the mother. Considering that the fetus becomes larger in size and the central nervous system is more mature, this always leads to birth injuries.
The most accurate way to determine the duration of pregnancy is through ultrasound tests. With modern equipment, it is possible to determine the gestational age of the future child. Additionally, the duration of pregnancy can be calculated by adding 266 days to the first day of the last menstrual period. It is important to remember that this date is only approximate. If the baby is born any time after 37 weeks, it is already considered normal.
The duration of pregnancy can be determined using various methods. Regardless of the chosen method, one should focus on the following factors:
Even after determining the approximate due date for the baby, it is important to remember that the main task for the future mother is to await calmly and love the future child. To avoid unforeseen developments, it is necessary to regularly consult with the attending physician, 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. It can only be applied if the cycle is regular and has the same interval.
For example, if the cycle lasts an average of about 35 days (in comparison, many women have a cycle of 26-28 days), then conception is most likely to occur on the 21st day of the cycle, not on the 14th, as with a 28-day cycle. Therefore, the calculated term by this method will be a week longer than the actual obstetric duration of pregnancy.
You can obtain the obstetric due date by adding two weeks to the known date of conception. Even if a woman knows the date of ovulation or the date of intercourse that led to conception, it doesn’t mean she knows the conception date with absolute accuracy. The fact is, after entering the female body, a sperm can lead to conception for up to 5 days, sometimes even longer.
In the meantime, a mature egg can be fertilized within 2 days after ovulation. During this time, it remains capable of conception. Because of this, it’s not possible to rely solely on the exact date of intercourse or ovulation. There are no exact guarantees that conception occurred on that specific day. The actual date of conception could be earlier or later. Therefore, the duration of pregnancy determined by this method cannot be considered absolutely accurate.
The pregnancy duration is calculated somewhat differently if it results from IVF. In this case, the fertilization of the egg by a sperm is managed by an embryologist. The development of embryos in laboratory conditions lasts for 3-5 days, after which they are transferred into the uterus.
The true duration of a pregnancy achieved through IVF is calculated by doctors starting from the date the ovarian puncture was performed. This is one of the procedure stages when follicular fluid is collected and fertilization occurs. From the date of the ovarian puncture, two weeks are added—this allows for determining the obstetric term.
If the embryo was frozen in liquid nitrogen before being transferred to the uterus (a process known as cryopreservation), the exact duration of the pregnancy can only be determined by adding 5 days to the transfer date. To find out the obstetric term, add 14 days to the obtained true duration.
During a woman’s examination on the gynecological chair, the doctor uses both hands to determine the size of the uterus. This also helps to estimate the approximate duration of the pregnancy. This method of determination demonstrates the greatest accuracy in the early stages of carrying a child—up to about 12 weeks. The earliest term that can be determined by uterine size is 5 weeks.
By this time, there is a slight increase in the uterus, as well as its softening. It acquires a more rounded shape. At later stages, the size of the uterus may vary depending on the size of the fetus, the amount of amniotic fluid, and the structure of the mother’s pelvis. For example, it is generally considered that at 16 weeks (4 months), the uterine fundus is located in the middle of the distance between the pubic bone and the navel, and at 24 weeks (6 months), the uterine fundus is already at the level of the navel.
In the early stages, it is possible to determine the duration of pregnancy with the greatest accuracy. For this, an ultrasound is performed, during which the size of the gestational sac and embryo are measured. In the first trimester, a small “black circle” is identified — this is the gestational sac, followed by the appearance of the embryo. By the end of the first trimester, this embryo will look like a small “line.” Also, its heartbeat becomes distinguishable at this time.
The pregnancy duration is considered more accurate when calculated by the measurement of the embryo’s CRL (crown-rump length). After 12 weeks, the gestational age by ultrasound is determined considering the so-called fetometry. Thus, in determining how many months the pregnancy will last, various measurements of the fetus are considered — from the length of the arms to the head.
During the second trimester, the embryo grows proportionally. Due to this, its size will be approximately the same in all women with the same pregnancy duration. Later, the size of the fetus in expectant mothers will differ. This is completely normal as it is influenced by many factors, from the mother’s weight to the father’s age. In this case, it becomes impossible to accurately determine the duration of pregnancy using an ultrasound examination.
If, at later stages, the fetus appears to be smaller than expected, doctors often consider this a developmental disorder. It is generally linked to the placenta not fully transporting oxygen and nutrients.
hCG is a hormone produced by the placenta throughout the months of carrying a baby. It is the first to signal a successful conception of the child. Its amount gradually increases up to the 11th week, and then begins to gradually decrease. In the first months, determining the concentration of hCG in the blood helps accurately determine the duration of pregnancy.
Once the tests are received, it should be noted that laboratory tests indicating the hormone level’s correspondence to the delivery date typically show the embryonic term. To determine the usual obstetric duration of pregnancy, 14 weeks should be added to the obtained date.
Recently, texts for determining the duration of pregnancy by urine have become particularly popular. Their operating principle is directed at identifying the concentration of the hormone in a pregnant woman’s urine. It is important to remember that this test specifically identifies the embryonic period.
This method of determining the term shows the least accurate results and is therefore used quite rarely. It is based on the belief that women who are giving birth for the first time start to feel the baby’s first movements around the 20th week, while women who have given birth before feel them earlier — at 18 weeks. This is why many obstetricians-gynecologists recommend accurately remembering when the fetus first moved and recording this data in the exchange card.
This method of determining the duration of pregnancy often shows errors. Indeed, women who are expecting their first child start to feel fetal movements later than women who already have children. This is simply related to the experience of the women, who can easily identify the baby’s movements and know the sensations that accompany them.
Quite often, women compare the first fetal movements to the sensation of liquid flowing in the abdomen. Generally, the first movements are rare and irregular. Moreover, the mother’s sensitivity plays a very important role in this.
There is another detail: slim women usually feel fetal movements earlier compared to women who are overweight. If the mother leads an active lifestyle and works a lot, the movements become noticeable much later. Once the term is determined, the doctor can calculate the approximate duration of the pregnancy. On average, the obstetric term is 280 days or 40 weeks.
To ensure a complication-free pregnancy, it is necessary to adhere to certain recommendations:
If there have been previous premature births or risk factors arise, the doctor may prescribe a course of progesterone injections—this can help normalize the condition of the expectant mother and her child. Thus, the normal duration of pregnancy is 40 weeks. Premature or overdue births can be determined by several factors. Additionally, there are several methods actively used to calculate the duration of the pregnancy.
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