23.01.2021

Date of birth and how to calculate it

The expected date of birth begins to interest the woman from the first day when she found out about her situation. The approximate birthday of a child can be calculated in several ways, but none of them can boast 100% accuracy. Many factors can influence the pregnancy process, and childbirth often turns out to be premature or late.

What determines the duration of labor

Even in a healthy woman who has a healthy baby, the date of birth can deviate from the estimated time and depends on:

  • from whether she gives birth for the first time or repeatedly;
  • from the duration of the menstrual cycle;
  • from heredity and other individual characteristics of the mother;
  • from the features of intrauterine development of the baby;
  • on how many children are in the uterus.

In the presence of chronic diseases in a woman, a violation of the intrauterine development of the child, acute diseases or injuries during pregnancy – the term of delivery can significantly deviate from the planned date.

Methods for determining the date of birth

The most common methods for determining the estimated date of birth are as follows:

  • by the date of the last menstruation;
  • by time of ovulation;
  • by date of conception;
  • by ultrasound;
  • the size of the uterus;
  • on the first stirring of the fetus.

Let’s consider each in more detail.

By date of last monthly

Monthly delivery date is the most common way to determine.

It has been used by obstetrician-gynecologists for many decades, because:

  • not all pregnant women know the time of the last ovulation or the date of conception during regular sexual activity, but everyone remembers when they had their last menstruation;
  • This is a pretty accurate method.

To determine the day of birth, you need to remember the first day of the last menstruation, add 1 year to this date, then subtract 3 months, and then add 1 week. The calculated date will be a guideline for the expected birth. Another way of determining: add 9 months and 1 week to the first day of the last menstruation.

By time of ovulation or presumptive conception

The method of calculating the date of birth by the date of conception can be used with a planned pregnancy, when a woman specifically calculated the days of ovulation and knows them. It is during this period that conception occurs. 266 days are added to the first day of ovulation and the date of delivery is calculated on the calendar. This method is called embryonic.

By date of sexual intercourse

This method is convenient to use for irregular or rare sex life. In this case, the woman knows which day in her life was decisive. Everything is very simple – 266 days are added to this date. This method is closer to embryonic. The birth dates calculated by these two methods may differ by only a few days, because the date of sexual intercourse and conception often do not match. Not everyone knows that some sperm can live in a woman’s body for up to 9 days, waiting in the wings.

By ultrasound

Using an ultrasound scan, the doctor can determine the approximate duration of labor based on the established age of the fetus. Most precisely, this is established in the first trimester of pregnancy. In the future, there may be an error from a few days to 3 weeks.

The size of the uterus

The ancient medical method was an approximate determination of the gestational age and, accordingly, the expected birth by the size of the uterus. As in the previous case, it is possible to more accurately establish the time of birth in the early stages of pregnancy. In the future, the size of the uterus depends on many factors (the size of the fetus, the amount of water). In addition, this method is only suitable if there is 1 child in the uterus.

On the first stir of the fetus

An old folk way of guessing the date of birth is to move the baby. After the disappearance of menstruation, a woman could only suspect a pregnancy, but when the fetus began to move, it was a wholly sign.

The woman added 20 weeks to this date and could quite accurately guess the term of labor with small errors. It should be borne in mind that multiparous mothers are already familiar with the feeling of fetal movement in the uterus and, as a rule, they feel it 1-2 weeks earlier than the primiparous.

Calculation Efficiency

The exact day of childbirth cannot be determined, because the period from 38 to 42 weeks of pregnancy is considered a normal period for delivery. Thus, as many as 28 days can be considered the date of delivery “on time”. However, in the normal course of pregnancy, different calculation methods approximately coincide and circulate around one date in the range of +/- 14 days.

Gynecologists officially still use calculations to determine the possible day of birth for the last month, therefore this term is called obstetric. In approximately 20% of cases, this method guesses the date of birth with an accuracy of +/- 5 days, and this is a rather high percentage. The exact coincidence of the date of birth and obstetric term is about 5%.

How the features of the menstrual cycle affect the date of birth

Regardless of the duration of the menstrual cycle, the obstetrician-gynecologist applies the formula for calculating the term of labor by the date of the last menstruation. Accordingly, women with a short cycle and a long one will have the same date of birth. However, the date of ovulation is different for them, so the conception and the term of delivery will be different.

With a short menstrual cycle (24 days),  ovulation occurs on the tenth day. Fertilization occurs on ovulation days. Therefore, the actual period for women with a short cycle will be expected a week earlier. The date of birth is calculated according to the following formula: the date of the first day of the last menstrual period plus 1 year and minus 3 months.

With a long cycle (35 days),  ovulation occurs on the twenty-first day. Delivery will be a week later than the gynecologist calculated. A woman can calculate the date this way: the date of the first day of the last monthly plus 1 year, minus 3 months and plus 14 days.

Calculate the date of birth with an irregular menstrual cycle with large jumps follows the classical formula.

When you cannot use the obstetric method of calculation

The obstetric method of determining the date of birth by the last monthly is the most common.

But it is not possible to use it in the following cases:

  • when pregnancy occurs immediately after the previous birth, and menstruation has not yet been;
  • with severe menstrual irregularities, when the interval between menstruation can be more than several months, as is the case with menopause or various female diseases, for example, polycystic ovaries or hormonal disorders.
What can be deviations from the terms

The bearing of a child lasts 9 calendar months, or 10 lunar months (28 days each), or 280 days.

Childbirth is classified into urgent, premature and late:

  • Delivery in 38-42 weeks is a normal period. Statistically, 70% of mothers give birth in the range of 39-41 weeks. Nulliparous often give birth 1 week later than the established normal term. But with repeated birth, on the contrary, women more often give birth before 39 weeks.
  • Delivery after 42 weeks is late. The child is considered to be postponed. There are about 9% of such births.
  • Delivery before 38 weeks is premature. The viability of the baby depends on the gestational age during delivery. The closer this period is to normal, the better.

Everything is individual, and during preterm birth a completely healthy and mature baby can be born, more often this happens for a period exceeding 35 weeks. If the baby is underweight – less than 2500 grams, it will be considered premature.

The second degree of prematurity is established with a delivery period of 32 to 35 weeks and a baby weighing less than 2000 g. However, he also has a lot of chances to “ripen” and gain weight after birth without the use of hardware life support.

In preterm birth from 28 to 31 weeks, the baby will be preterm 3 degrees and low in body weight (from 1000 to 1500 g). Such children are successfully nursed in perinatal centers.

At the birth of a baby for a period of 22-28 weeks, he will have a 4th degree of prematurity. The baby has extremely low body weight and undeveloped lungs. There is no surfactant substance that provides free breathing of the child.

Previously, fruit from 700 grams was considered viable, now it weighs 500 grams or more. Such children are nursed in intensive care units using special plastic transparent boxes – cuvezes, which provide the necessary temperature, humidity and sterility of the environment. The baby is connected to an artificial lung ventilation apparatus, feeding is carried out intravenously or via a probe, the necessary drug therapy is provided. More About Premature Babies →

A child born earlier than 22 weeks will be unviable due to severe immaturity. Such kids are currently not able to go out of medicine.

Causes of Preterm Birth

The total share of all preterm births is about 10% of cases. The cause may be the pathology of the mother or fetus, or a combination of various factors.

The most common ones are: 

  • Social – smoking, alcohol abuse, drug use, stress, extreme physical activity, malnutrition and hypovitaminosis.
  • Uterine pathology – the consequences of abortion, cesarean section, other operations on the uterus, hypoplasia, endometritis, endometriosis.
  • The pathology of the ongoing pregnancy is placental abruption, oligohydramnios, premature discharge of amniotic fluid, inflammation of the membranes, multiple pregnancy, gestosis.
  • Maternal diseases – diabetes, hypertension, rheumatism, bronchial asthma, severe anemia, mental disorders and more.
  • Multiple abnormalities in the development of the child, incompatible with life, at present the latter is rarely the cause of premature birth, as women try to terminate the pregnancy in the early stages for medical reasons.

In the presence of such risk factors, a woman should be especially careful, as she has a high risk of giving birth to a premature baby. She may have to spend some time on conservation.

Determining the estimated date of birth is an important task. But in any case, the calculated period is approximate. It depends on many reasons. Therefore, with a long gestation period, a woman should listen to herself and expect a birth, starting from the 37th week of pregnancy, or even earlier.

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