Calculation of pregnancy, methods for determiningweekly calculator

Update: October 2018

Any woman preparing to become a mom is looking forward to
the appearance of two cherished strips on the test. After this point
there are excitements and experiences. Is the baby developing normally,
when you need to go on the first ultrasound, and finally, when are coming
childbirth? All these questions can be answered, knowing the exact date
of pregnancy.

What is gestational age?

Very often, confusion in the head of a pregnant woman occurs
because of the misunderstanding of this term. Therefore it is important to know when
embryo development begins, and when the countdown to

The ovum after ovulation (leaving the ovary) lives for about a day.
This time is considered the most favorable for conception. With
menstrual cycle in 28 days ovulation occurs on day 14. AT
the moment of fertilization, the sperm cell merges with the egg cell, and through
week the developing embryo attaches to the inner lining

Since most women have a menstrual cycle
inconstant, then the exact date of ovulation and conception no one knows.
Therefore, all midwives of the world are considered to be the beginning of pregnancy.
The first day of the last menstruation. 9 months (280 days) after
On this day, birth must take place. AT этом и состоит парадокс: отсчет
pregnancy has already begun, and conception has not yet been. Therefore, the lifetime
embryo shorter gestation by an average of 2 weeks.

Methods for determining the duration of pregnancy and the date of birth

  • First Trimester Ultrasound
  • Formula Negele (by the date of the last menstruation)
  • Examination of a pregnant doctor (determination of the size of the uterus)
  • Evaluation of hCG
  • Movement of the fetus

ATсе врачи мира определяют срок беременности по одному
the main parameter (ultrasound) and two auxiliary (date of menstruation
and inspection of a pregnant woman).


The main method is ultrasound. ATажно помнить, что
The accuracy of this method is maximum in the first 10-12 weeks, and then
she falls. Byэтому именно Ultrasound первого триместра широко применяется
для определения предполагаемой даты childbirth.

Modern devices can determine the fetal egg in the uterus already with
3-5 недель of pregnancy. As the embryo grows to 3-4 mm
it becomes possible to measure its CTE (coccyx-parietal size),
which serves as the basis for determining the term of gestation with precision
until the day. Usually, in the conclusion, the doctor indicates exactly what time he is
means: obstetric (since the last menstruation) or
embryonic (since conception).

After 22 weeks of gestation, determine the exact age of the fetus.
is impossible. But the measurement of its main parameters (head size,
femur length, abdominal circumference) allows you to evaluate
growth dynamics. If it does not meet the deadline stated at
Ultrasound в 1 триместре, то есть вероятность синдрома задержки развития
fetus. In addition, there are individual hereditary features
(short stature, large head), due to which in the third trimester
срок беременности расчету по Ultrasound не подлежит.


Last menstruation date – calculator

Determination of gestational age by the last menstruation day –
the most affordable way for women. If the expectant mother is happy
owner of a regular cycle in 28 days, then she can
самостоятельно и довольно точно рассчитать дату childbirth. For this
There are special formulas for Negele.

PDR = PDPM – 3 months + 7 days

  • DA – Estimated Date of Delivery
  • PDPM – the first day of the last menstruation

For example, if the PDPM was June 15, then PDR = June 15 is 3 months +7 days
= March 15 + 7days = March 21. Date determination is based on this.
родов во всех специальных калькуляторах расчета срока of pregnancy.

ATведите первый день последних месячных:

Day Month Year

The period of gestation is determined by adding to the MAP number
weeks after that day. Therefore implement with
normal calendar calculation of pregnancy can each

When can not determine the period of menstruation?

  • Irregular menstrual cycle. With цикле, превышающем 35
    days, ovulation does not occur on day 14. Therefore, the Negele formula
    will give an inaccurate result (see the reasons for the violation
    menstrual cycle).
  • Withем противозачаточных средств. With несоблюдении регулярности
    taking oral contraceptives may happen pregnancy. By
    reason for sudden ovulation formula for calculating da also does not fit
    (see pros and cons of oral contraceptives).
  • With угрозе прерывания беременности ранних сроков. It happens
    that there is a threat of termination of pregnancy in the smallest terms.
    Very often, it is manifested by scant bleeding in
    days corresponding to the expected menstruation. That is, a woman can
    confuse bleeding at 5 weeks gestation and normal
    monthly, and will not even guess his interesting
    position AT таких случаях определяют срок с помощью Ultrasound.

Examination of pregnant

Byстановка каждой беременной на учет в женскую консультацию
starts with inspection. Sizing uterus and the height of her standing
bottom (that is, the upper part) can give indicative information about
сроке of pregnancy. This method is not 100% accurate. ATедь
individual location of the uterus, myoma and full bladder
may make inspection difficult. A multiple pregnancy is associated with
a large increase in this organ.

HCG level

Already in 8-10 days after conception in the blood of the future mother
определяется AT-субъединица ХГЧ. This hormone appears during
pregnancy and doubles every 2-3 days (see hCG standards for
weeks). To judge the duration of gestation on its level can only

  • ATо-первых, нормы ХГЧ для каждой недели беременности имеют
    large range.
  • ATо-вторых, его уровень возрастает при многоплодной беременности
    и некоторых аномалиях развития fetus. Byэтому нет смысла
    focus on this hormone when calculating the duration of pregnancy by
    неделям, когда доступны более точные методы (Ultrasound, например).

Date of first stir

It is believed that primiparous women feel fetal movements with
20 недели of pregnancy. Byвторнородящие могут ощутить их уже с
16-18 weeks. In fact, it all depends on the individual
features of mom and baby, the thickness of the fat layer on the abdomen
pregnant and from her desire to feel the tremors. In addition, often
for the first movements take intestinal peristalsis. Byэтому не
It is worth relying on this indicator in calculating the term
of pregnancy.

How to determine the duration of pregnancy with IVF?

With экстракорпоральном оплодотворении многие женщины
сомневаются, как правильно считать недели of pregnancy. ATедь в
the uterus cavity is planted already developing embryo. But
regardless of the method of fertilization (naturally,
insemination of sperm or IVF) pregnancy is determined by
first day of the last menstrual period. The only exception is possible
count IVF with menstruation suppression protocol (superlong
protocol). AT этом случае срок отсчитывается от дня подсадки
embryo with the addition of two weeks.

Why do doctors determine the exact duration of pregnancy?

  • To assess fetal growth rates
  • To determine the date of birth
  • For screening for chromosomal mutations (Down syndrome
    and etc.)
  • To determine the viability of the child with premature

The main purpose of determining the period of gestation for the future mother –
tune in to the imminent birth of the baby and meets
information on intrauterine development by week.

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