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How to calculate gestational age by weeks and days

Modern technologies help future mothers to calculate the exact gestational age at a very early stage. An accurate estimation of the dates of conception and labor is a very important process as it helps to take good care of the health of both mother and child.

Doctors have several options of diagnosing the gestational age, and each of them is good in its own way. In addition, there are methods of establishing the date of conception that can be applied at home.

What is the obstetric week, and how does it help in determining the gestational age

Usually, the first thing a woman does having discovered a late period is she tries to determine pregnancy using special techniques. A variety of tests provide relatively accurate results, so, next, she goes to the doctor with an inquiry about pregnancy. It is important not only to establish the existence of pregnancy, which is quite simple, but also to calculate the gestational age based upon conception or menstrual period.

All experts calculate the obstetric gestational age, and it’s taken in consideration when assessing the condition of mother and fetus. The period from the first day of the last menstrual period until delivery is called the obstetric period, and it usually consists of 40-42 weeks. Below you can see how the obstetric gestational age is calculated by weeks and months.

Gestational age by weeks and days

Another question is what is the obstetric week of pregnancy? This is a key concept in the detection of pregnancy, but not all women are able to correctly count obstetric weeks.

As mentioned above, the calculation of the obstetric period begins from the first day of the last menstrual period. During this period the eggs begin to mature, the body is reconstructing and conception is most likely. So, the countdown begins perhaps even before a woman becomes pregnant, from the maturation of her eggs. It is believed that the period of gestation lasts 40-42 weeks from the first day of the last menstrual period until actually giving birth. The obstetric week, as usual, consists of seven days.

[attention type=yellow]Why do we need to calculate the duration of the pregnancy exactly this way? The fact is that it’s virtually impossible to find exact date of conception. Often, even though a woman knows when sexual intercourse took place, she still has doubts. But any woman knows the date of the beginning of her last menstrual period, and with the help of that date, it is possible to determine when ovulation occurred, and consequently, the conception.[/attention]

How to calculate the expected gestational age and exact due date of delivery with the help of obstetric weeks? A woman needs to recall when was the first day of her monthly period, and count from that time to the present day. This will be the term of pregnancy.

To determine the date of delivery it is necessary to recall the day of the last menstrual period, and count 280 days from it. This will be the expected date when you will meet your long-awaited baby. This method has an error margin, but usually it is small – 3-7 days. In the table below, you can choose the first day of the last menstrual period and below it, you will see the expected date of birth.

How to calculate gestational age by weeks and days - delivery

Of course, these are far from all medical methods of determining the gestational age. Modern technologies have incredibly progressed, and doctors offer a variety of methods, although each of them has its own problems.

Medical methods of determining of the gestational age

So, how else can gestational age and due date of delivery be calculated, and how accurate are such calculations?

How to calculate gestational age by weeks and days - US
  • Calculate gestational age by ultrasound.
  • Determine the gestational age by uterine size.
  • Calculate the gestational age by the last menstrual period.
  • Determine the gestational age via hCG analysis.

The most common way to determine the gestational age is by ultrasound, but it has its own margin of error. The gestational age is calculated based on the size of the fetus and its development. By looking at the dimensions, doctors can establish the approximate gestational age.

[attention type=yellow]However, the method of determination by ultrasound is not considered to be the most accurate, because the sizes of babies are strictly individual. For example, a completely healthy baby can be born of a smaller size, than average, or, perhaps, much bigger than that. And yet it is very important to have an ultrasound examination because it helps to identify possible pathologies in fetal development. That is why doctors recommend to have an ultrasound as often as possible, especially in the last terms of pregnancy.[/attention] Gestational age by weeks and days - hCGAnother great method is an hCG blood test. This option helps to optimally determine the right term in the earliest stages of fetal development. At this time, the amount of hormones in the blood increases as much as twofold. Experts recommend analyzing blood every other day, at least three times in a row. This method has a relatively small margin of error.

The gynecologist can determine the term also by uterine size. For that purpose, a thorough inspection must be carried out. For example, in the first obstetric month, the uterine size reaches the size of a chicken egg. By the third obstetric month, the uterine size is approximately equal to the diameter of a baby’s head, its asymmetry disappears, and the uterus itself fills the upper part of the pelvic cavity.

By the fourth month of pregnancy the uterus is positioned midway between the pubis and the navel. Using uterine dimensions, a gynecologist can define the term during a scrupulous examination of the woman.

However, the date of conception can be determined not only by gynecological methods, but at home, as well. It is true that such home methods can be quite inaccurate.

How to calculate the gestational age at home

Many women prefer to rely on home methods for determining the gestational age, so they do not immediately go to the doctor even knowing about conception. Now, there are many ways to determine the date of conception at home, and here are some of them:

How to calculate gestational age by weeks and days at home
  • Calculate the period of conception by the last period.
  • Calculate gestational age by the ovulation date.
  • Calculate gestational age by the conception date.
  • Determination of the age by the first movement of the baby.
  • Using the online calculator to determine the week of pregnancy.

The easiest way to determine the moment of conception is to recall the date of the last unprotected intercourse. If a woman believes that sexual intercourse was the only one in a long time, then she should count her pregnancy from this day. The possibility of miscalculation is there, but usually only by 2-4 days. However, this period of pregnancy will somewhat differ from the obstetric calculations by 2 weeks, and the estimated due date will not be in the 40th week.

Having recalled the beginning of the last menstrual cycle, a woman can also successfully calculate her gestational term. This method is fairly accurate, especially if the woman keeps a calendar account of the start and end dates of her menstrual periods.

Another method to calculate the gestational age is the baby’s movement. If this is the first pregnancy, the woman will feel his movements in about the twentieth week. If a woman gives birth for a subsequent time, then the baby’s movement will be felt in the eighteenth week. Of course, before that time you must visit a specialist and consult with him about the pregnancy.

Now you can calculate the gestational age by weeks with an online calculator which accurately and clearly gives a woman an expected due date and the period of possible conception. And having calculated the term, you can then view on the weekly pregnancy calendar what happens to the mother and baby. All that is required from a woman, is to enter the start date of her last menstrual period. This calculator of gestational age, of course, has a small margin of error of 3-5 days, but in fact its calculations match those that are usually carried out by gynecologists.

[attention type=green]But which method is used by the readers of our article? You can share your valuable experience in the comments section. Maybe your advice regarding how to calculate the gestational age by weeks can help someone become happy parents.[/attention]

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