2024 Author: Josephine Shorter | [email protected]. Last modified: 2024-01-07 17:49
Calculate due date
Date of birth calculator
Determining the gestational age and the expected date of delivery is very important for both the woman and her leading doctor. Many laboratory and instrumental studies are prescribed precisely at the time when it is easiest to identify pathology in time. Comparison of the parameters of the fetus with the average indicators of each period of pregnancy helps to identify and correct underdevelopment. Clarity in determining the date of birth of a child allows you to carefully prepare for this event and open a sick leave in time so that the woman has time to gain strength before giving birth.
There are several methods to help you calculate the metrics you need. The obstetrician-gynecologist uses them in combination, since almost every method has a permissible error associated with subjective reasons: the individual characteristics of a woman, elementary forgetfulness - it is difficult to remember the date of the last menstruation. The term of the expected birth can be determined rather approximately, since a full-term pregnancy lasts from 38 to 42 weeks, and this is normal from a physiological point of view.
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Formula Negele
The method of calculating due date using this formula is great for women with a constant standard cycle of 28 days. The Negele formula is simple - to determine the desired date, subtract 3 months from the first day of the last menstruation, and then add 7 days to the resulting figure. If the menstrual cycle was constant, but lasted more or less than the standard, the difference between your and the standard cycle should be added to the resulting date, or the same number of days should be subtracted.
It can be calculated even easier - add 280 days (or 40 weeks) to the start date of the last menstruation.
How to calculate due date by ovulation date?
If a woman in the month preceding conception determined the onset of ovulation by basal temperature, this will help to accurately establish the gestational period. Conception occurs on the day of ovulation, when the egg cell ready for fertilization leaves the ovary. If sexual intercourse took place 1-2 days before ovulation, the sperm remain ready for fertilization all this time, that is, conception can occur a short time after sexual contact. If you add 38 weeks, or 266 days, to the date of ovulation, you can find out the estimated date of birth of the child.
If a woman does not know when ovulation occurred, but has a stable 28-day menstrual cycle, it is assumed that conception occurred in the middle of the cycle, that is, on day 14. With an irregular cycle, this method has an error.
We determine the date by the movement of the child
The date when the woman first felt the movement of the baby is very important for correcting the complex calculation of the expected due date. Although the fetus begins to move from the twelfth week, the first time most women feel these gentle movements in the middle of the gestational period, that is, at the twentieth week. However, this rule does not apply to everyone - during the second and subsequent pregnancies, a woman may feel the first movements 2 weeks earlier.
A primiparous woman of a fragile constitution also has such an opportunity, while a pregnant woman, who has a solid build, feels movements later. These feelings can be called subjective, because they depend on the woman's sensitivity to what is happening in her body. The thickness of the myometrium also affects the severity of the child's movements.
All these nuances mean that the above method for determining the date of birth cannot be considered the main one, it is used only in combination with other methods.
How do obstetricians-gynecologists consider the gestational age?
When calculating the gestational age, the doctor usually relies on the date of the beginning of the last menstruation, however, the main calculations are carried out taking into account a set of various criteria.
By the size of the uterus
In the early stages of pregnancy, when individual differences in fetal size are not yet apparent, it is possible to determine the date of birth using this technique. For a period of 4 weeks, the size of the uterus is compared with a chicken egg, for a period of 8 weeks - with a goose.
From the twelfth week, this method is already difficult to apply, since in the future, the parameters of the uterus and fetus differ in different women with the same period.
By ultrasound
The method for determining the term of labor according to ultrasound scanning data is valid at the beginning of the gestational period, more precisely, until the third month. After twelve weeks, it is impossible to accurately determine the date of delivery, based on ultrasound data, due to individual differences in fetal parameters in women of different constitutions.
By the height of the fundus of the uterus
This method has been used by the obstetrician-gynecologist since the beginning of the second trimester. The longer the fetus develops, the higher the bottom of the organ becomes, which rises beyond the pelvis.
The height of the fundus of the uterus is determined when the woman is lying on her back. The doctor gently palpates the abdomen and measures the distance from the symphysis pubis to the fundus of the uterus. This indicator increases evenly throughout the gestational period, and immediately before childbirth, the uterus drops.
When using this technique, an error of 2-3 cm is laid. It can be caused by polyhydramnios, pregnancy with twins or triplets, the age of the woman, the size of the fetus. To clarify the indicators, the waist circumference of the pregnant woman and the parameters of the fetus are taken into account.
Calculating the height of the bottom of the uterus by week:
- 8-9 weeks - height 8-9 cm, the uterus is still located within the pelvis;
- 10-13 weeks - height 10-11 cm, the uterus increases, the placenta develops intensively, the fetal cardiovascular system begins to work;
- 16-17 weeks - height 14-18 cm, the uterus is between the navel and the pubic joint, the fetus looks like a little man, all organs of which are already laid;
- 18-19 weeks - height 18-19 cm, the unborn child develops arms and legs with fingers, the cerebellum, the immune system, the placenta takes full responsibility for ensuring the functioning of the fetus;
- 20 weeks - the height of the uterus in centimeters corresponds to the gestational age in weeks;
- 21 weeks - height 21 cm, from that time the height of the uterus will increase by 1 cm weekly, now it is 2 fingers below the navel.
- 22-24 weeks - height 22-24 cm, the fundus of the uterus at the level of the navel, easily determined by palpation, the fetal body weight is 0.6-0.7 kg;
- 25-27 weeks - height 25-28 cm;
- 28-30 weeks - height 28-31 cm;
- 32 week - height 32 cm, the upper edge of the uterus is located between the xiphoid process of the sternum and the navel;
- Week 36 - height 36-37 cm, the uterus is felt on the line of the costal arches connection;
- Week 39 - height 36-38 cm, the uterus begins to descend, the weight of the fetus exceeds 2 kg;
- 40 weeks - the height of the uterus is reduced to 32 cm, it is again between the navel and the ribs, the baby is ready for delivery.
By head size and fetal length
The following methods are used to calculate the gestational age:
- Jordania's method. The term is calculated by the formula X = L + C, where X is the term in weeks, L is the fetal body length (cm), C is the diameter of its head (cm).
- Skulsky's method. Here the formula is as follows: X = (L x 2) - 5/5, where L is the fetal body length (cm), the number 5 in the numerator of the fraction is the thickness of the myometrium, and the number 5 in its denominator is a special coefficient.
Any calculations are only a rough guideline. According to medical statistics, only 10-17% of babies are born on time, the rest are born earlier or later than expected. This circumstance is influenced by many factors: heredity, pregnancy pathologies, stressful situations and other reasons.
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