What Is the Length of Pregnancy? How to Calculate It Right?

length of pregnancy. pregnant woman holding the clock

The vast majority of pregnant women want to know everything about the development of the baby, and this is right. An informed mother will better cope with the difficulties that may arise. At first, the main question for many women is about the length of pregnancy. Basically it is necessary to determine the date of birth. But no matter how much you want it, no one can tell the exact date of birth, since each pregnancy is unique in its own way. In addition, it is impossible to predict how the woman’s body will behave in relation to her new condition.

9 Months or 40 Weeks?

We are all used to the fact that the duration of pregnancy is calculated in months. But the whole point is that in obstetrics there is no such a thing as months. Therefore, very soon a future mother finds out that from now on she will count how many weeks, not months, her pregnancy lasts.

The duration of pregnancy in medicine is indeed determined by weeks. To completely form and be ready for independent life outside the mother’s womb, the fetus needs at least 38 weeks.

The maximum period that a child can spend in the mother’s womb is 42 weeks. However, it is considered that the normal gestation period usually does not exceed 40 weeks. After this time, the risk of complications in the fetus and the mother increases. For those who want to know the exact figure of the length of pregnancy, doctors respond: pregnancy lasts at least 266 days.

length of pregnancy. fetus stages

Keep in mind that these terms, although they are generally accepted, are rather relative. The organism of every future mother is individual. That’s why it is impossible to accurately predict how long she will be pregnant. Even in the same woman, the course of pregnancies can be quite different.

The Average Length of Pregnancy

How long does the pregnancy last? Unfortunately, it’s impossible to know exactly the date of birth. The date, called by the doctors, is only the estimated date of delivery.

There are cases when the actual date of birth coincides with the expected date. But all these cases are nothing but simple coincidences.

Even if a woman knows exactly the day of conception and the date of ovulation, it is impossible to determine the speed of the sperm, how many days the egg moves through the fallopian tubes, when exactly it is implanted, what time the fetus needs to fully mature and when the baby is ready to be born.

Since all our organisms are individual, in each case these processes proceed in different ways. That’s why physicians use the average statistical standard to orient.

So how many weeks does a woman’s normal pregnancy last? Scientists have estimated that in 80% of cases from the time of fertilization to the onset of labor, 266 days pass. Respectively, this is equal to 38 weeks. But the difficulty in this calculation lies in the fact that, as a rule, future mothers do not know the exact day of conception.

The Basis of Calculation

At the same time, they usually remember the date of the last menstruation. That’s why this date was taken as the basis of the calculation. Thus, it turns out that 40 weeks pass from the day of menstruation to delivery. Therefore, the length of pregnancy is 40 weeks (280 days).

However, it’s clear that pregnancy did not occur on the first day of menstruation. Therefore, the time calculated in this way is approximate. It is called menstrual or gestational period.

length of pregnancy. happy pregnancy

In fact, the age of the fetus is about two weeks less. This period is more precise. It is called ovulation or fertilization period. In order to determine the date of their birth more accurately, future mothers should calculate the date of their ovulation.

How to Calculate the Date of Ovulation?

It is hard to believe, but in each month there is only one day when it is possible to become pregnant. In very rare cases, during the month this day comes twice.

There is a simple formula for calculating the day of ovulation without additional devices. Scientists found out that ovulation occurs in the middle of the cycle. Thus, if the menstrual cycle lasts 28 days, it turns out that ovulation will come on the 14th day.

This calculation is very simple. However, this method is suitable only for those women who have a regular cycle. In addition, you can calculate the day of ovulation only if there is an accurate cycle schedule within at least six months.

Moreover, in individual cases, ovulation may occur a little earlier, or, a little later. But, if the exact date is taken as a point of reference, then it appears that the pregnancy lasts for 266 days (280-14 = 266).

That is why, doctors call pregnancy normally termed if it lasts from 266 to 294 days or from 38 to 42 weeks.

length of pregnancy. trimesters

When counting, it is easy to see that 280 days (40 weeks) are just 9 months. However, obstetricians have their own months count. According to their calculations, the pregnancy lasts 10 months. The fact is that the so-called lunar months are included in the calculation. They consist of 28 days. This is the period of the duration of the cycle in most women.

Factors Affecting the Length of Pregnancy

First of all, the length of pregnancy is affected by the health of the future mother and other factors. For example:

  • heredity;
  • psychological condition;
  • fetal development;
  • intrauterine condition.

In case of premature birth, as well as prolonged pregnancy, there are additional threats of unfavorable births, which can affect the health of the fetus and the mother.

These phenomena may be due to neuroendocrine disorders, illnesses in the past and previously committed abortions. According to statistics, women who have been treated for the threat of miscarriage are more likely to have prolonged pregnancy. A prolonged pregnancy is the one, the term of which has crossed the line of 42 weeks.

Prolonged Pregnancy


Many future mothers are more afraid of premature birth than of a prolonged pregnancy. However, in fact, it is very dangerous.

Physicians still cannot give an exact answer, why sometimes pregnancy lasts longer than it should. But usually doctors single out two factors – medical and psychological one.

From a medical point of view, the cause of the problem lies in the fact that a woman is physically not ready to give birth.

This can be explained by the following factors:

  • Late maturation of the cervix;
  • Muscular disorders of the uterus and myometrium;
  • Delayed development of the fetus;
  • Hormonal problems;
  • Endocrine and gynecological diseases of a woman;
  • Pathology of the uterus;
  • Heredity.

Moreover, the duration of pregnancy depends on the age of the mother. Most often, the first but late pregnancy can become a prolonged one.

length of pregnancy. prolonged pregnancy

All the reasons that can be attributed to the medical aspect are identified through additional surveys. But the psychological side is difficult to identify.

It may happen that psychologically a woman is not yet ready for childbirth. The reason for this lies in the unconscious fear of the birth processes. A woman can be afraid of pain or the possibility of losing a child. As a result, this may slow the onset of the natural process down.

At the first signs of prolonged pregnancy it is worthwhile to see a doctor. Having made an additional ultrasound, the specialist will be able to determine the condition of the placenta, amniotic fluid and, of course, the child.

When, after the ultrasound, meconium traces are found in the amniotic fluid or problems with the child’s palpitation are revealed, then in this case the doctor will definitely prescribe birth stimulation or a cesarean section. Do not reject these appointments. The consequences of a delayed pregnancy can be tragic.

The Consequences

In 40% of cases, during late delivery, placental dysfunction occurs. Thus, it is not able to provide the child with the necessary amount of nutrients and oxygen.

Very often, with a prolonged pregnancy, the fetus gains excess weight, which naturally complicates the process of delivery.

In the child’s body, too little subcutaneous fat is observed. This retards the baby’s growth. In addition, during childbirth, which began after 42 weeks, the possibility of birth injury is higher.

Most often it is expressed in Erb’s palsy, fractures of limbs and collarbones, and also in dysplasia of the hip joint.

In this case, the mother is also exposed to an additional risk, which includes the following:

  • the probability of perineal incisions is high;
  • risk of uterine damage;
  • protracted labor;
  • occurrence of bleeding in the postpartum period.

This condition is called the pathology of pregnancy for a reason. Therefore, you should consult a doctor to avoid such unpleasant consequences.

It is much more useful to be psychologically and physically prepared for childbirth in the last days of pregnancy. During this period, future mothers also need better rest.

Childbirth is a difficult process for the body of any woman. That’s why you should spend enough time sleeping. Many women attend specialized courses, in which specialists tell how to make childbirth easier and safer.

Moreover, now you can find a lot of supporting information that will make you more confident and eliminate unnecessary fears. The main thing to remember is that after giving birth, you will finally meet the most important person in your life.

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