Determining the date of birth: exact calculation methods

2024 Author: Priscilla Miln | [email protected]. Last modified: 2023-12-16 00:21

Pregnancy is a happy and long-awaited event for many women. And often with the discovery of two cherished strips on the test, the expectant mother is faced with many questions. Aside from waiting for signs of pregnancy, speculation about the baby's gender, he alth concerns, and research, the question is "How to calculate due date?". Usually, at the first visit, the doctor determines the approximate gestational age, conducts an examination, gives directions for various tests, and calculates the preliminary date of delivery. Subsequently, with subsequent diagnostics, these figures may vary.

Pregnancy term

Pregnancy is the process from conception to the birth of a child, lasting 9 months, 40 weeks or 280 days. Gestational age can be measured by two methods: obstetric and fetal. Obstetric is calculated from the first day of the last menstruation, which is considered the first day of pregnancy. Embryonic - the period from the very conception. Usually these terms differ in 2 weeks. In obstetrics and gynecology for pregnancy managementdoctors use the calculation of the period from the first day of the last menstruation. This is due to the fact that all women are unique, each menstrual cycle has a different duration, the dates of ovulation and conception are usually unknown.

Date of birth

Predicting the due date cannot be completely accurate. The date is approximate, as no one can predict when the baby will be ready to be born. The gestational age and the expected date of delivery are set in order to assess the development of the fetus, conduct timely studies if necessary, and give an approximate idea of when the baby may be born.

Possible timing of the baby's birth

Professional doctors use a standard set of three ways to determine the due date: last menstruation, ultrasound and gynecological examination. However, the timing of actual delivery is not so predictable. Some women will give birth at term, others before, and still others after. Only 5 percent of children are born on time. Up to 10% of children are born before the 37th week, about 14% of pregnancies last longer than 42 weeks. From here, delivery times can vary from the 37th to the 42nd week.

Premature births before 37 weeks gestation:

• Extremely premature babies are born between 23 and 28 weeks.
• Moderately premature babies are born between 29 and 33 weeks
• Late premature babies are born between 34 and 37 weeks.

Children,those born before 39 weeks of gestation are at higher risk for breathing problems, low blood sugar, and other problems that may develop on admission to the neonatal intensive care unit or as they grow up.

Determining the date of birth

So how do you calculate your due date? When to expect the birth of a long-awaited child? In obstetrics and gynecology, there are the following methods for determining the expected date of birth:

• According to the last menstrual cycle.
• By date of conception/ovulation.
• According to ultrasound.
• Based on gynecological examination.
• By the date of the first movements.

Determining the date of delivery by the last menstruation

The Ministry of He alth defines the stages and duration of pregnancy a little differently than it might seem. Logically, one can imagine that the countdown of pregnancy begins from the moment of conception. But instead, the onset is measured from the date of the last menstrual period. One of the reasons is that it is impossible to know exactly the day of conception (except in cases of fertilization). And every woman usually knows the first day of the previous cycle. Therefore, they use the definition of the date of birth by the last menstruation.

A normal menstrual cycle can vary from 21 to 35 days, usually 28 days. Therefore, when a doctor tells a woman that her gestational age is six weeks after the start of her last menstrual period, it means that she has become pregnant aboutfour weeks ago, around ovulation.

The expected duration of pregnancy is 280 days from the first day after the start of the last menstrual cycle (four weeks longer than the traditional nine months that many believe). Medical professionals consider preterm births before the 36th week, and extremely preterm when the baby is born before 28 weeks after the start of the last period.

Sometimes gestational age is measured in trimesters. The first trimester is usually up to 12 or 14 weeks. The second trimester runs from the end of the first to 28 weeks, and the third trimester runs from the end of the second until delivery.

How to calculate due date from last menstrual period? With a regular 28-day cycle, seven days should be added to the first day of the last menstruation and then three months should be subtracted. Accordingly, with the last menstruation on December 10, 2017, the approximate date of delivery is September 17, 2018.

Determination by date of conception

In the case when the date of conception is known, you can determine the approximate day of birth by simple mathematical calculations, namely, add 266 days. This is approximately how long a pregnancy lasts, if you count from conception or ovulation. But this method cannot be 100 percent correct, since the onset of ovulation and sexual intercourse performed on that day does not mean at all that conception has occurred. The sperm cell travels a long way before it meets the egg and fertilizes it. Therefore, it is possible that conception took place for severaldays later. Theoretically, with a standard 28-day menstrual cycle, ovulation occurs in its middle on the 14th day. For longer cycles, you can find out the approximate date of ovulation using ultrasound diagnostics or using special tests.

In in vitro fertilization (IVF) and other assisted reproductive procedures, the day of embryo transfer is considered the date of conception. In this case, the egg has already been fertilized, therefore, in artificial insemination, the determination of the date of birth by the date of conception is reliable.

Ultrasound

Ultrasound can also be used to determine gestational age and date of birth, especially when the date of last menstruation is not known. It happens:

• If pregnancy occurred after a recent birth in the absence of menstruation. Usually, after delivery, some time must pass for the normalization of the hormonal background of a woman and the formation of the menstrual cycle. If a woman is breastfeeding, then the period of absence of menstruation is usually extended until the end of lactation.
• When irregular cycle. In such situations, the cycle may not be the usual 28 days, but more than 40 or even 60 days. It is not possible to predict and predict the date of ovulation without additional diagnostics.

When determining the date of delivery by ultrasound, the doctor is based on a series of measurements of the ovum and fetus as the pregnancy progresses. Ultrasound examination helps to most accurately determine the date of birth in early pregnancy. In the first trimester, the age of the fetus is determined with an error of 3-5 days. Up to 20 weeks, the error is 7-10 days. By the third trimester, gestational age and fetal development can differ by as much as 3 weeks in either direction. Late-term ultrasound is used more to assess the growth and development of the baby compared to previous studies than to predict the due date.

All pregnant women undergo an ultrasound examination according to the plan 3 times:

• At 11-14 weeks. Screening for chromosomal abnormalities, assessment of fetal size, location of placenta, amniotic fluid level.
• At 18-20 weeks. Scanning aimed at examining the anatomical structure of the fetus, presentation, exclusion of deviations from the norm, assessment of cardiac activity.
• At 32-34 weeks. Study of the volume of amniotic fluid, assessment of fetal development, presentation, exclusion of deviations from the norm, assessment of cardiac activity.

Estimation of gestational age and date of birth is most effective when performing ultrasound diagnostics in the first trimester. Measurement of the coccyx-parietal size of the fetus allows you to almost accurately determine the gestational age. Thus, ultrasound is the most reliable method for determining the expected date of delivery.

First movements

It used to be that a woman pregnant for the first time had fetal movements at about 20 weeks. At the same time, multiparous people noticemovements of the child earlier - at 18 weeks. But already after the lapse of time, it was found that in all pregnant women the fact of the appearance of fetal movements is determined at different times. Therefore, at present, the determination of the date of birth by the first movement in gynecology is not used. It all depends not only on the number of pregnancies, but also on the anatomical features of women, their body structure, physical fitness, and lifestyle. Someone can feel the baby's movements at 16 weeks, others much later - at 22. Thin people usually begin to feel the baby's tremors earlier than full ones. Active exercisers feel later, while women with more relaxed pastimes have more time to focus on their sensations. Therefore, this method of determining the expected due date is not informative.

Gyno exam

The fact of pregnancy and the approximate date can be established during examination by a gynecologist. During the examination at 12 weeks, the uterus can be palpated above the pubic bone, above the navel, starting from the 20th week. The uterus usually rises above the navel by about a centimeter a week. This measurement is called fundal height and is usually measured from 24 to 34 weeks. For example, at 28 weeks, the height of the uterine fundus is usually about 28 cm. But on examination, the ability to determine the date of delivery may be erroneous due to factors such as multiple pregnancies, uterine tumors, or obesity.

Other methods

SimilarThus, the estimated date of delivery is determined by the heartbeat of the fetus. Heart sounds can be heard with Doppler starting at 9-12 weeks and with a stethoscope after 20 weeks. In this case, the calculation result will be very approximate.

In closing

It is worth remembering that any of the methods for determining the expected date of birth does not give a 100% guarantee that the long-awaited child will be born on this day. Of course, if the woman is not scheduled for a caesarean section, in this case the date of the operation is known in advance. It is worth remembering that each pregnancy is unique, and the baby will be born only when it is ready for it. A normal pregnancy usually lasts between 38 and 42 weeks.

Regardless of how the expected date was calculated, you need to be ready for the birth of a child in about two weeks. Buy all the necessary things, make repairs, assemble furniture, prepare things for the hospital and for discharge, so that later no troubles overshadow this significant event.