Pregnancy is a happy and long-awaited event for many women. And often with the discovery of two treasured stripes on the test, the expectant mother is faced with many questions. In addition to expecting signs of pregnancy, assumptions about the baby’s gender, health concerns and research, the question arises, “How to calculate the date of birth?” Usually, at the first visit, the doctor sets the approximate gestational age, conducts an examination, gives directions for various tests and calculates the preliminary date of delivery. Subsequently, with subsequent diagnosis, these figures may vary.
Gestational age
Pregnancy refers to the process from conception to the birth of a child, lasting 9 months, 40 weeks, or 280 days. Pregnancy can be measured by two methods: obstetric and embryonic. Obstetricians are calculated from the first day of the last menstruation, which is considered the first day of pregnancy. Fetal - the term from the very conception. Usually these terms vary in 2 weeks. In obstetrics and gynecology for the management of pregnancy, doctors 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, the menstrual cycles for each of various durations, the dates of ovulation and conception are usually unknown.
Date of birth
Predicting a preliminary birth date may not be completely accurate. The date is approximate, since no one can predict when the baby will be ready to be born. The gestational age and the expected date of birth are established in order to assess the development of the fetus, conduct timely studies as necessary, give an approximate idea of when the baby can be born.
Possible dates of birth
Professional doctors use a standard set of three methods for determining the term of delivery: according to the last menstruation, ultrasound and gynecological examination. However, the timing of actual delivery is not so predictable. Some women will give birth on time, others before, and still others after. Only 5 percent of babies are born on time. Up to 10% of babies are born before the 37th week, about 14% of pregnancies last longer than 42 weeks. Hence, the delivery time can vary from the 37th to the 42nd week.
Premature birth is considered to begin before 37 weeks of pregnancy:
- Extremely premature babies are born from the 23rd to the 28th week.
- Moderately premature babies are born between the 29th and 33rd weeks
- Late premature babies are born between the 34th and 37th weeks.
Children born before 39 weeks of pregnancy have more risks of breathing problems, low blood sugar and other problems that may appear when they are admitted to the intensive care unit or as they grow older.
Birth Date Determination
So how do you calculate the date of birth? When to wait for the long-awaited baby to be born? In obstetrics and gynecology, there are the following methods for determining the estimated date of birth:
- According to the last menstrual cycle.
- By date of conception / ovulation.
- By ultrasound.
- Based on a gynecological examination.
- By the date of the first movements.
Determining the date of birth according to the last menstruation
The Ministry of Health defines the stages and duration of pregnancy in a slightly different way than it might seem. It is logical to imagine that the countdown of pregnancy begins from the moment of conception. But instead, the onset is measured from the date of the last menstruation. One reason is that it is not possible to know the exact day of conception (except in cases of fertilization). And the first day of the previous cycle is usually known to every woman. Therefore, the determination of the date of birth by the last monthly is used.
A normal menstrual cycle can vary from 21 to 35 days, usually 28 days. Therefore, when a doctor tells a woman that the gestational period is six weeks after the start of the last menstrual cycle, this means she became pregnant about four weeks ago, around the time of ovulation.
The expected duration of pregnancy is 280 days from the first day after the start of the last menstrual cycle (four weeks more than the traditional nine months, which many people think). Medical specialists consider it premature to give birth when they occur before the 36th week, and extremely premature when the baby is born before 28 weeks after the start of the last menstruation.
Sometimes pregnancy is measured in trimesters. The first trimester, as a rule, is up to 12 or 14 weeks. The second trimester lasts from the end of the first to 28 weeks, and the third trimester - from the end of the second until delivery.
How to calculate the date of birth according to the last menstruation? With a regular 28-day cycle, seven days should be added to the first day of the last month and then subtract three months. Accordingly, with the last menstruation on December 10, 2017, the approximate date of birth is September 17, 2018.
Determination by date of conception
In the case when the date of conception is known, the approximate day of birth can be determined by simple mathematical calculations, namely, add 266 days. Pregnancy lasts approximately as long as it is counted from conception or ovulation. But this method cannot be 100 percent correct, since the onset of ovulation and sexual intercourse performed on this day does not mean at all that the conception has occurred. The sperm cell travels a long way before meeting the egg and fertilizing it. Therefore, it is possible that conception occurred a few days later. Theoretically, with a standard 28-day menstrual cycle, ovulation occurs in its middle on the 14th day. With 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 is already fertilized, therefore, with artificial insemination, the determination of the date of birth by the date of conception is reliable.
Ultrasonography
Ultrasound diagnostics can also be used to determine the gestational age and date of birth, especially when the day of the last menstruation is not known. This happens:
- If pregnancy has occurred after a recent birth in the absence of menstruation. Usually, some time should pass after delivery to normalize the hormonal background of the woman and the formation of the menstrual cycle. If a woman is breastfeeding, then the period of absence of menstruation usually stretches until the end of lactation.
- With an 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 assume and predict the date of ovulation onset without additional diagnosis.
When determining the date of birth by ultrasound, the doctor is based on a series of measurements of the fetal egg and fetus as pregnancy progresses. An ultrasound study helps to determine the date of birth in the early stages of pregnancy most accurately. 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, the gestational period and development of the fetus can differ by as much as 3 weeks in any direction. In the later stages, ultrasound diagnostics are mainly used to assess the growth and development of the child compared to previous studies than to predict the date of birth.
All pregnant women undergo an ultrasound examination according to the plan 3 times:
- At 11-14 weeks. Screening for exclusion of chromosomal abnormalities, assessment of fetal size, placenta location, amniotic fluid level.
- At 18-20 weeks. Scanning aimed at examining the anatomical structure of the fetus, presentation, elimination of deviations from the norm, assessment of cardiac activity.
- At 32-34 weeks. Study of amniotic fluid volume, assessment of fetal development, presentation, exclusion of abnormalities, assessment of cardiac activity.
Evaluation of gestational age and date of birth is most effective when conducting ultrasound diagnostics in the first trimester. Measurement of the coccygeal-parietal size of the fetus allows you to almost accurately determine the gestational age. Thus, ultrasound is the most reliable method for determining the estimated date of birth.
First stir
It was previously believed that a woman who was pregnant for the first time had fetal movements around 20 weeks. At the same time, the multiparients notice the child's movements earlier - at 18 weeks. But already over 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, determining the date of birth by the first stir 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, lifestyle. Someone can feel the baby moving at 16 weeks, others much later - at 22. The thin ones usually begin to feel the baby's tremors earlier than the full ones. Actively engaged in physical education feel later, while women with a calmer pastime have more time to focus on their feelings. Therefore, this method of determining the estimated date of birth is not informative.
Gynecological examination
The fact of pregnancy and an approximate period can be established during the examination of the gynecologist. During the examination at 12 weeks, the uterus can be felt over the pubic bone, over the navel, starting from the 20th week. The uterus usually rises above the navel about a centimeter per week. This measurement is called the height of the uterine fundus 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 when examined, the possibility of determining the date of birth can be erroneous due to factors such as multiple pregnancy, uterine tumors, or obesity.
Other methods
Similarly, the estimated date of birth is determined by the fetal heart rate. Heart sounds can be heard with dopplerography, starting from 9-12, and with a stethoscope after 20 weeks. In this case, the calculation result will be very approximate.
Finally
It is worth remembering that any of the methods for determining the estimated date of birth does not give a 100% guarantee that a long-awaited baby will be born on this day. Of course, if a woman does not have a cesarean 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 from 38 to 42 weeks.
Regardless of how the estimated 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 at the hospital and for discharge, so that subsequently no troubles would overshadow this momentous event.