How to determine the duration of pregnancy?

The term of pregnancy is set by the gynecologist at the first visit of the expectant mother to the antenatal clinic. There are a number of important reasons for determining the exact duration of pregnancy. Knowing the gestational age, you can monitor the development of the fetus and correct the likely lag in its intrauterine development, and most importantly, you can set the expected date of birth.

Types of terms of pregnancy

There are two types of terms of pregnancy.


Obstetric term begins its countdown from the first day of the last menstruation. This happens because it is from this day that the egg cell begins to develop, which is subsequently fertilized by the spermatozoon. A zygote is formed and then implanted into the uterus. From the zygote the fetal egg develops with the embryo, and after 12 weeks of gestation the embryo becomes the fetus.


The true time comes obstetric for two weeks. Its countdown starts from the day of ovulation and conception. Therefore, in order to calculate the true gestational age, you simply add two weeks to the obstetric period.

How to determine the duration of pregnancy and the date of delivery?

There are several ways to determine the duration of pregnancy and the expected day of birth.

On the first day of the last menstruation

There is a method of Negele, in which they make a countdown from the first day of the last menstruation: from this date three months ago and then add 7 days. The received date and will be an approximate day of delivery.

By date of the first movement of the baby

If a woman gives birth for the first time, then to determine the date of birth, 20 weeks are added to the date of fetal movement. If a woman is multiparous, then add 22 weeks. But this method of determining the duration of pregnancy and childbirth is not the main one, since the sensation of movement is usually quite subjective. A woman may be confused by the movement of the baby with the processes occurring in her intestines.

Female counseling visit

The doctor can also determine the approximate date of birth. Undoubtedly, it is important that the woman turned to the antenatal clinic as early as possible, after the establishment of pregnancy. The error can be avoided or minimized if the woman turns in the first 12 weeks of pregnancy.

There are several objective signs on which to determine the duration of pregnancy:

  • the size of the uterus;
  • height of the bottom of the uterus;
  • volume of the abdomen;
  • the length of the baby and the size of his head.

To determine the timing of the objective signs, the doctor focuses on existing criteria.

For example, in the fourth week of pregnancy (first obstetric month), the uterus becomes about the size of a hen's egg, in the eighth week (second obstetric month) the size of the uterus with a goose egg, and in the twelfth week (third obstetric month) the uterus reaches the size of the fetal head.

Determining the duration of pregnancy, it is safer to refer to the most reliable methods (determination by the date of ovulation; ultrasound).

The knowledge that the established period is only approximate, is of great importance for the mental balance of the future mother. After all, a woman is set up on a specific date of delivery, and if the contractions do not occur at the appointed time, she is experiencing great stress. There is fear and anxiety for the health of the baby, which can lead to attempts to stimulate childbirth. Hospitalization ahead of time will bring only more anxiety and negative emotions.

Only the baby knows when it is better for him to be born. Any established period of pregnancy and intended delivery, even when using a combination of different methods, cannot be one hundred percent accurate.