The doctor in the LCD talks about some obstetric weeks of pregnancy, the ultrasound sets a completely different period, and according to your calculations, the third is obtained. And how can an inexperienced future mommy not get confused here. In fact, everything is not so difficult, you just need to deal with some of the nuances.
What is an obstetric term and why is it needed?
Obstetric weeks pregnancies include the period from the first day of the last pre-pregnancy period to the expected due date (PDD). The obstetric period is 280 days or 40 weeks, or 10 obstetric months (a month is 28 days). Obstetric weeks of pregnancy are counted even when conception has not yet occurred, but the processes of maturation and release of the egg have successfully passed.
The definition of obstetric weeks is necessary for the convenience of calculating the timing of pregnancy. After all, no doctor can say for sure when a woman had ovulation and, accordingly, conception. And the woman herself can, of course, guess about the possible day of conception, but not be completely sure of it. Meanwhile, as the date of the beginning of the last menstruation is remembered by almost all the fair sex.
What is embryonic term and ultrasound term of pregnancy?Fetal term is the life span of your baby, first as an embryo, and then as a fetus. The embryonic period lasts approximately 265-266 days (38 weeks or 9 normal months).
Ultrasound examination determines the estimated duration of pregnancy based on the available size of the baby, while relying on the standard indicators of its development at embryonic (up to 12 weeks) and obstetric (after 12) weeks. The ultrasound timeline is rather imprecise. The size of the fetus, like the size of an adult, is individual, small children are born, heroic children are born, a slight deviation (no more than 2 weeks from the norm for the corresponding week of pregnancy) is allowed. Nevertheless, the definition is very important, a significant deviation from the standard indicators indicates various pathologies in the development of the baby.
How to count obstetric weeks of pregnancy?
The doctor should tell the expectant mother about what and how the obstetric weeks of pregnancy are considered. But if suddenly he did not cope with his task, and you forgot to clarify this point with him on your own, the following information is for you.
So how to calculate obstetric pregnancy weeks? It's pretty simple. Take the calendar, remember the date of the first day of the last menstrual period, count from this day (including with it) the number of days or weeks (as you like) until today, you get. If you counted in days, do not forget to divide the resulting number by seven. If you want to know the date of the expected birth, use the same scheme to calculate 280 days. You can determine the PDR in a different way, namely: according to the same calendar, count three months from the first day of the last menstruation back and add 7 days.
How are obstetric weeks and fetal weeks different?Based on the above, the difference between obstetric and fetal weeks of pregnancy is the order in which they are counted. Obstetric term 
is 280 days (counted from the last menstruation). Meanwhile, embryonic lasts approximately 265 days (count from the day of conception).
If a woman's menstrual cycle was regular and stable, then with a high percentage of probability it can be assumed that ovulation occurred in the middle of the cycle and in the middle of the cycle, respectively, conception occurred. That is, the time difference between obstetric weeks of pregnancy and embryonic weeks in a healthy woman with regular menstrual cycle duration of 28-30 days is within two weeks. In women with an irregular cycle, the embryonic period can only be guessed at.
So, your suspicions about pregnancy have been confirmed. And now you are most concerned with the question: when did the miracle happen? When did the conception take place, and when is the birth now expected?
Obstetric and actual gestational age
The gestational age is calculated by obstetric weeks, there are forty of them in total (in the normal course of pregnancy). It is a mistake to think that they are calculated from the moment of conception. The starting point is the start date of the last menstrual period, the one that ended with conception.
During the first obstetric week of pregnancy, your future child exists, one might say, only in the form of a maturing egg. During this period, the endometrium of the uterus is also rejected and prepared for a new cycle.
During the second week from the onset of menstruation, the ovarian follicle, which releases the egg, matures and bursts. Ovulation occurs on day 13-16, and the following two to three days - the best time to try to conceive a child.
If it succeeds and the sperm has joined with the target, then at the end of the third week from the beginning of menstruation, the fertilized egg divides and moves along the tube to the uterus. The third obstetric week is the first week of the actual (embryological) pregnancy, which is counted from the moment of cell fusion.
During the fourth obstetric week (from the beginning of menstruation), a fertilized egg - a blastocyst - is implanted into the endometrium and, with a successful pregnancy, forms a fertilized egg. At this time, the corpus luteum in the ovary begins to "work" in pregnancy, and the change in hormonal levels already affects your well-being.
In the fifth week after the last menstruation, the next one should already begin. If this does not happen, suspicions about pregnancy increase.
Determining the actual timeframe using tests
By the fifth obstetric week, the concentration of the hormone hCG (human chorionic gonadotropin) in the urine reaches such a level that a rapid test can show two stripes. But this does not always happen, or the second strip may be barely visible. This happens when ovulation is later than usual. As soon as both strips on the test become equally bright, you can be sure: the pregnancy is uterine, the embryological (actual) period is two to three weeks.
If you remember the exact date of intercourse that led to conception, then add five more days to this number to establish a starting point for the actual pregnancy. You may have even felt the attachment of the blastocyst: sometimes it is accompanied by general deterioration feeling of well-being, lethargy, a slight increase in temperature.
Be that as it may, when registering, the gynecologist will still ask you about the start date of the last menstrual period, since it is on obstetric weeks that all examinations are prescribed, as well as going on maternity leave (hospital for pregnancy and childbirth). The due date is indicated exactly 40 weeks after the start of the last menstrual period.
To make sure that the pregnancy is uterine and developing normally, the obstetrician-gynecologist may prescribe you an ultrasound of the pelvic organs. The direction will indicate the period in obstetric weeks, but the specialist on the study will most likely indicate a shorter period - just those two weeks that precede conception. It shouldn't scare you, pregnancy ultrasound early term- a very inaccurate procedure, the ovum and embryo can be of different sizes and shapes with their normal development.
With further examinations, the period indicated by the doctor at the site and the ultrasound period will be equal to 20-23 weeks. The duration of the cycle in women is different, while the average period of 28 days is taken to calculate the period for obstetric weeks, ovulation also does not always occur in the middle of the cycle, which explains the discrepancies in determining the duration of pregnancy.
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Maria Sokolova
Reading time: 8 minutes
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The obstetric method of calculating pregnancy by week is different from the usual one. A month consists of 28 days, not 30-31. The period is usually considered by the gynecologist from the first day of the last menstruation. The waiting period for the baby is only 40 obstetric weeks.
Consider how the fetus develops weekly, and also determine how mommy feels at all stages of pregnancy.
1 obstetric week
The fetus is a follicle that appears on the surface of the ovary. There is an egg inside it. The female body does not feel it, but only prepares for fertilization.
Symptoms of conception at 1 week of pregnancy are not observed. And all because the fruit does not manifest itself in any way. The expectant mother will not even notice the changes.
2 obstetric week
At this stage of development, ovulation occurs. As soon as the ovum matures in the follicle, it is released from it and is sent through the fallopian tube to the uterus itself. It is during this period that the sperm gets to it and merges together. This forms a small cell called a zygote. She already carries the genetic material of both parents, but does not manifest herself.
The body of the expectant mother can behave differently at 2 weeks after conception: signs of PMS may appear, mood changes, she wants to eat more or, on the contrary, will turn back from food.
3 obstetric week
On the 14-21th day of the menstrual cycle, the fertilized cell joins the uterine layer of the endometrium and is placed in a special water sac. The embryo in this period is very small - 0.1-0.2 mm. His placenta is forming.
In a pregnant woman, hormones change at 3 weeks. PMS symptoms may be noticeably expressed: the chest will begin to swell and ache, the lower abdomen will pull, and the mood will change. In addition, early toxicosis may appear.
But many women did not have such signs at this stage of pregnancy.
4 obstetric week
At the 4th week of conception, the fetus establishes a bond with its mother - an umbilical cord is formed, through which the baby will feed for all 9 months. The embryo itself consists of 3 layers: ectoderm, mesoderm and endoderm. The first, the inner layer is responsible for the creation of such organs in the future as: the liver, bladder, lungs, pancreas. Second, middle words are needed to build the muscular system, heart, kidneys, circulatory system, and gonads. The third, external, is responsible for the skin, hair, nails, teeth, eyes, ears.
In the mother's body, malaise, drowsiness, irritability, nausea, soreness of the mammary glands, improved appetite, and fever may occur.
5 obstetric week
At this stage, the embryo develops some of the makings of the nervous and respiratory systems, as well as fully develops the heart and blood vessels. The fetus weighs only 1 gram and its size is 1.5 mm. At 5 weeks after conception, the baby's heart begins to beat!
Symptoms in a pregnant woman are as follows: morning toxicosis, enlargement and pain in the chest, fatigue, drowsiness, increased appetite, sensitivity to odors, dizziness.
6 obstetric week
Your baby's brain is forming, arms and legs, eye fossa appear, and folds in the place of the nose and ears. Muscle tissue also develops, the embryo begins to feel and manifest itself. In addition, the rudiments of the lungs, bone marrow, spleen, cartilage, intestines, and stomach are formed in him. At 6 weeks from conception, the fetus is the size of a pea.
Despite the fact that a third of pregnant women do not notice changes in the body, women may have fatigue, frequent urination, toxicosis, abdominal pain, mood changes, and breast enlargement.
7 obstetric week
At this time, the child develops very quickly. It weighs 3 g, and its size is 2 cm.He forms five parts of the brain, develops nervous system and organs (kidneys, lungs, bronchi, trachea, liver), the optic nerves and the retina of the eyes are created, the ear and nostrils appear. Little by little, the baby has a skeleton, the rudiments of teeth. By the way, the fetus has already developed a four-chambered heart and both atria are working.
In the second month of pregnancy, mood changes as well. A woman notices rapid fatigability, she wants to constantly sleep. In addition, working capacity may decrease, toxicosis may appear, heartburn and bloating may suffer. In many pregnant women, blood pressure drops during this period.
8 obstetric week
The baby already looks like a person. Its weight and size does not change. He is like a grape. On the ultrasound, you can already make out the limbs and the head. The baby actively manifests itself, turns over, squeezes and unclenches the hands, but the mother does not feel it. At 8 weeks after conception, all organs are already formed in the fetus, the nervous system is developed, the rudiments of male and female genital organs appear.
A pregnant woman in the second month may feel discomfort in the lower abdomen, as the uterus will enlarge and will be the size of an orange. In addition, toxicosis manifests itself, appetite changes, mood changes, working capacity decreases, and frequent urination appears.
9 obstetric week
At the beginning of the third month of pregnancy, the cerebellar region is formed in the fetus, which is responsible for the coordination of movements. In a child, the muscle layer increases, the limbs thicken, palms are created, the genitals appear, the kidneys and liver begin to work actively, the back straightens and the tail disappears.
The expectant mother feels unpleasant sensations, also gets tired quickly, suffers from toxicosis, does not get enough sleep, but feels better than last week. The breast increases dramatically during this period.
10 obstetric week
The size of the fruit is almost 3-3.5 cm. At the same time, it actively grows and develops. The baby develops chewing muscles, forms the neck and pharynx, creates nerve endings, olfactory receptors, taste buds on the tongue. Bone tissue also develops, replacing cartilage.
The pregnant woman also suffers from toxicosis and frequent urination. Weight gain, groin and chest pains, and sleep disturbances may occur.
11 obstetric week
The embryo of this period is already clearly moving, it reacts to external stimuli (smell, food). He develops a digestive system, genitals. At 11 weeks from conception, rarely does anyone determine the sex of the baby. All other organs gain weight and develop further.
A woman may be upset for no reason, want to sleep or refuse to eat. Many people can suffer from toxicosis, constipation and heartburn. There should be no other unpleasant manifestations.
12 obstetric week
At the end of 3 months of pregnancy, the internal organs of the small embryo were formed, its weight doubled, human features appeared on the face, nails appeared on the fingers, and the muscular system developed. The child is already wrinkling his lips, opening and closing his mouth, clenching his fists and swallowing food entering the body. The little man's brain is already divided into two hemispheres, and testosterone is produced in boys.
Mom is starting to feel better. The malaise, fatigue disappears, he runs less to the toilet, but the change in mood also remains. There may be constipation.
13 obstetric week
At 4 months, the little man develops the brain and bone marrow, the respiratory system, and thin skin appears. The baby feeds through the placenta, this week it is finally formed. The weight of the fruit is 20-30 g, and the size is 10-12 cm.
A woman at the 13th week may suffer from constipation, seizures and changes in blood pressure. She feels better and is awake. Some people still have morning sickness.
14 obstetric week
This week, the fetus is rapidly gaining weight, its organs and systems are improving. The crumb weighs about as much as an apple - 43 g. It has cilia, eyebrows, facial muscles and taste buds. The child begins to see and hear.
Mom now eats with great pleasure, her appetite appears, her breasts and abdomen increase. But there are also unpleasant sensations - shortness of breath, pulling pains in the lower abdomen. Stretch marks may appear.
15 obstetric week
At this time, it is already possible to determine the sex - the genitals are formed in the fetus. The child develops legs and arms, ears, and the first hairs grow. The kid is gaining weight, his bones are getting stronger.
The expectant mother feels more vigorous, toxicosis and weakness go away. But shortness of breath, stool disturbance may remain. Blood pressure will be lowered. Dizziness will remain and the weight will increase by 2.5-3 kg.
16 obstetric week
At the end of 4 months, according to obstetric calculations, the fetus already weighs like an avocado and fits on your palm. His organs and especially the digestive system are actively beginning to work. He already reacts to voices, hears and feels, moves. Those mothers who are pregnant with their second child may feel a wiggle in their tummy.
An expectant mother at the 16th week may complain of leg pain. The mood and well-being improves. Skin pigmentation may change.
17 obstetric week
At the beginning of 5 months, the baby becomes more like a newborn, since subcutaneous adipose tissue called brown fat is formed in him. He is responsible for heat exchange in the child's body. The fetus also gains weight. And he can also eat about 400 g of amniotic fluid. He develops a swallowing reflex.
Mom can feel the baby moving in the tummy, and the doctor can hear his heartbeat. The expectant mother in the 17th week of pregnancy will feel calm, happy and a little absent-minded. Some women will only be bothered by late toxicosis.
18 obstetric week
The fruit is actively developing, growing, moving, pushing. Fat folds form on the skin. In addition, the child begins not only to hear you, but also to distinguish between day and night. His retina becomes sensitive, and he understands when there is light outside the tummy, and when it is dark. All organs except the lungs function and fall into place.
Mom's weight at 18 weeks should already increase by 4.5-5.5 kg. The appetite will increase, as the baby will have to be fed. A pregnant woman may feel discomfort in the abdomen, and vision may deteriorate. A midline will appear on the tummy.
19 obstetric week
At this time, the nervous system and the brain of the fetus develop. The respiratory system and lungs are improved. His kidneys begin to work actively - to excrete urine. The digestive system is also on the verge of completion. The child actively manifests itself, gives signals and gains weight.
The mother should not have any health problems. In rare cases, nasal congestion, shortness of breath, constipation, heartburn, changes in blood pressure, cramps and discharge from the chest will appear.
20 obstetric week
The fetus also continues to develop - the immune system is formed, parts of the brain are improved, the rudiments of molars appear. Doctors are not mistaken with determining the sex at this stage of pregnancy.
Half of the term has passed. You should feel great. Some points may bother you: vision deterioration, shortness of breath, frequent urination, dizziness from low pressure, nasal congestion, swelling.
21 obstetric week
At 6 months old, all organs and systems have already been formed in a belly-lover, but not all of them function as they should. The child already lives according to the mode of sleep and wakefulness, swallows amniotic fluid, grows and gains weight. The pituitary gland, adrenal glands, sex glands, spleen begin to work.
A 21 week pregnant woman should feel good, but she may be bothered by pain in the abdomen and back. Shortness of breath, heartburn, swelling of the legs, frequent urination, stretch marks, increased sweating may appear.
22 obstetric week
The little man at this time actively begins to tactilely study his mother's belly. He grabs the umbilical cord with his handles, plays with it, sucks his fingers, can turn over and react to food, light, voice, music. The brain stops developing at 22 weeks, but neural connections are established.
Mom, as a rule, gets tired quickly and feels unwell. Since the baby is always moving, it is difficult for a woman to find a comfortable position for rest. The pregnant woman becomes very sensitive, reacts to smells, food.
23 obstetric week
The child is also actively moving, gaining weight. The digestive system is so well developed that he already eats about 500 g of amniotic fluid. At 23 weeks, the baby can already dream, the doctors will record the activity of the brain at your request. The child opens his eyes, looks at the light. He can even breathe - usually 55 breaths and exhalations per minute. But breathing is not constant yet. The lungs develop.
A 6 month pregnant woman has contractions. They are quite rare and manifest as mild cramps in the uterus. Of course, a woman is gaining weight, and if she is in an uncomfortable position, she may feel pain in her back and abdomen. Varicose veins and hemorrhoids may appear. Puffiness, pigmentation and nausea will appear.
24 obstetric week
In a fetus of this age, the development of the respiratory system is completed. Oxygen that enters the baby moves through the blood vessels. A baby born at 24 weeks can survive. The function of the fetus at 6 months is to gain weight. The expectant newborn also contacts the mother by pushing and moving.
The pregnant woman feels a surge of strength, is rapidly gaining weight. She may be worried about swelling of the face, legs, and the problem of sweating. But, in general, the state of health is great.
25 obstetric week
In the 7 month fetus, according to obstetric calculations, the osteoarticular system is strengthened, the bone marrow is finally improved. The baby weighs already 700 g, and his height is 32 cm. The baby's skin acquires a light shade, becomes elastic. A surfactant builds up in the lungs, which prevents the lungs from collapsing after the first breath.
A woman may suffer from the following troubles: heartburn, constipation, anemia, shortness of breath, swelling, pain in the abdomen or lower back.
26 obstetric week
The toddler gains weight, his muscles develop, and fat is stored. The lungs prepare to receive oxygen. Growth hormone is produced in the baby's body. The rudiments of permanent teeth appear.
The skeletal system is getting stronger. The baby is already moving in such a way that it hurts mom. Mom also suffers from heartburn, shortness of breath, and back pain. Anemia, swelling, and vision problems may occur.
27 obstetric week
The pupil actively trains all organs and systems. It weighs about 1 kg, and is 35 cm tall. The baby also senses extraneous sounds, senses touch, and reacts to light. His reflexes of swallowing and sucking are improved. When pushing, a mother may notice her baby's arm or leg.
The mother should be feeling well at week 27. It may be disturbed by itching, anemia, convulsions, changes in blood pressure, sweating.
28 obstetric week
At the end of the second trimester, the fetus becomes even more mobile. His brain mass increases, the grasping and sucking reflex is manifested, muscles are formed. The little man lives according to a certain routine - he sleeps for about 20 hours and is awake for the remaining 4 hours. The baby's eye membrane disappears, he learns to blink.
Mom at the end of the 7th month of pregnancy may feel itching, back pain, swelling of the legs, shortness of breath, heartburn. Colostrum appears from the mammary glands. There may be stretch marks on the body.
29 obstetric week
The baby has already grown up to 37 cm, his weight is 1250 g. The baby's body can regulate its temperature, its immune system works perfectly. The child is gaining weight, gaining weight, accumulating white fat. The baby is almost ready for existence outside the belly of the mother, who feels every movement of the little man. In addition, a pregnant woman gets tired of carrying, gets tired quickly, her appetite improves, shortness of breath and bouts of urinary incontinence may appear.
30 obstetric week
At 8 months old, the child is already quite developed. He feels the world around him, listens to the mother's voice. The kid lives according to his own sleep and wakefulness routine. His brain grows and develops. The fruit is very active. He can turn from the bright light, push Mom from the inside. Because of this, a woman will feel a slight pain in the abdomen, back, lower back. The load is also on the legs - they can swell. Also, a pregnant woman may feel shortness of breath, constipation, and bloating.
31 obstetric week
At this age, the baby's lungs are also improved. Nerve cells begin to work actively. The brain sends signals to the organs. The liver lobules are finishing their formation. The kid also grows and feels the world around him. His mom gets tired faster now. She may be worried about shortness of breath, swelling, late toxicosis and pain in the lower back and tummy.
32 obstetric week
There are no changes in fetal development. He is gaining mass and weighs 1.6 kg, and his height is already 40.5 cm. The child is also sensitive to smells, food, ambient sounds and light. And by the end of the 7th month, he takes a pose for birth. His skin takes on a light pink hue. The expectant mother can only complain of shortness of breath, frequent urination and swelling.
33 obstetric week
At the 8th month of pregnancy, the baby performs an important function - gaining weight. Now he weighs 2 kg, and his height is 45 cm. The nervous system develops in the baby, new connections are formed. The immune system is also still developing. The baby becomes less mobile, as it takes up all the space in its mother's uterus. A 33-week-old woman is feeling well. She may have shortness of breath, heartburn, leg cramps, back pain and itching.
34 obstetric week
The kid is already ready to get out. He gains weight and becomes 500 g more. His organs and systems are trained to function before going out. If the baby is born at 34 weeks, she can already breathe on her own. And the belly takes calcium from the mother's body and further builds bone tissue.
Mom may lose her appetite during this period. Back pain, shortness of breath, numbness, swelling will torment. Many women have contractions, but the pain in the upper abdomen should subside.
35 obstetric week
There are no significant changes in the development of the fetus. All organs and systems are simply debugging their work. Completing processes take place in the nervous and genitourinary systems. Meconium accumulates in the intestines. From this week, the child is rapidly gaining weight of 200-300 g. And his mother suffers from frequent urination, edema, heartburn, shortness of breath, insomnia. Contractions are also poorly expressed.
36 obstetric week
At the end of 8 months, the placenta begins to fade. Its thickness is small, but it fulfills its functions. The child is less active, sleeps more and gains strength before childbirth. Its systems and organs are developed. And the expectant mother may complain about the feeling of fatigue and possible contractions.
37 obstetric week
The baby is ready to be born this week. His eyesight and hearing have finally matured, an organism has formed. The child already looks like a newborn and is waiting in the wings. Mom, on the other hand, feels discomfort, pain. The contractions may recur more frequently. But breathing and eating will become easier. The stomach may sink. This phenomenon occurs several weeks before delivery.
38 obstetric week
The weight of the baby is 3.5-4 kg, and the height is 51 cm. The placenta, which connects the baby with the mother, is aging and loses its plethora. The fruit stops growing because it receives less nutrients and oxygen. The child sinks closer to the "exit" and eats through the mother's placenta. He is already ready for an independent life.
A pregnant woman feels heaviness in the lower abdomen. She may also be disturbed by frequent urination, leg cramps.
39 obstetric week
The baby will be on time this week. Girls are usually born earlier than boys. The kid is already viable. Mom, on the other hand, feels contractions. If they were not observed, a woman should never call them on her own. The expectant mother's mood changes, appetite disappears, and frequent urination worries.
40 obstetric week
The child is also waiting for the birth, gaining strength. It can grow up to 52 cm and weigh about 4 kg. The puzzler moves a little, but still reacts to mom's mood. A pregnant woman is usually ready to become a mother. She is worried about irritability, white-yellow discharge, pain throughout the body, nausea, heartburn, diarrhea, constipation, and, of course, contractions.
Modern experts use generally accepted norms regarding the bearing of a woman's fetus. Pregnancy without complications lasts an average of 280 days. Usually, the very beginning of the term means the first day of the last menstrual bleeding. This counting system is called obstetric timing. In modern gynecology, according to such data, the time of prenatal leave is calculated, the size of the fetus is estimated by ultrasound, and the estimated date of birth is calculated.
What is Obstetric Pregnancy Week?
The specialist, in order to determine the time of delivery by the obstetric method, counts exactly three months from the initial day of the last menstrual bleeding back, then adds 7 days to the result. It should be borne in mind that the resulting date of birth is not an exact day, but a certain range that can recede 10-12 days forward or backward from the most likely day of the natural birth of the fetus. Each pregnancy follows a unique scenario, so the time for carrying a baby varies. It is noticed that specialists mainly operate with the concept of obstetric term, because almost every unexpectedly pregnant woman can name the date of the last menstruation, since it is customary to record these data in the calendar, but few people will be able to accurately indicate the day when conception occurred.
A feature of the obstetric period of pregnancy is that it contains the full cycle of the birth of a new life, that is, the time from the beginning of the life of the egg, and until the appearance of a fully developed and ready for life in the external world of the child. There is nothing complicated in how obstetric weeks of pregnancy are counted. The week itself, as usual, is 7 days. The difference was found to be hidden in the number of months. We know that the gestation period is 9 calendar months, which is equal to 10 obstetric months, which is an average of 40 weeks - if you count from the date of your last period, and 38 weeks - if you start from the date of conception.
Obstetric gestational age: exceeds the embryonic term by 14-15 daysDetermining the duration of pregnancy
What is embryonic gestation?
It is known that in medical practice, the embryonic gestation period is also calculated, which begins with the fact of conception and, as a rule, coincides with the time of ovulation. A woman's menstrual cycle, lasting from the first day of her period until the first day of her next period, is usually between 28 and 30 days. During the first part of the cycle, the follicle matures inside the ovary; by the 14-15th day, the ovulation process is observed, implying the release of the formed egg from the follicle. It has been scientifically proven that after ovulation for about 2 more days, the egg retains the ability to fully further develop through fertilization. It is also taken into account that the sperm produced by a man are viable and prone to fertilization for about 4 days. It turns out that only 6 days have the highest probability of conception. Based on the foregoing, a feature of the obstetric term can be distinguished: it certainly exceeds the embryonic one. The difference between these concepts is 14-15 days.
Calculation of gestational age according to ultrasound
It is theoretically possible to calculate the gestational age based on the size of the uterus and the nature of fetal movements. These criteria cannot be considered accurate, because these are strictly individual data with a significant scatter. In fact, the fetus begins to move at 7-8 weeks of life, but the mother may feel tremors at 18-20 weeks. Every woman needs to have an idea of ovulation and fetal timing, monitor her own menstrual cycle, and at least in general terms know how obstetric weeks of pregnancy are counted. Having accurate data will facilitate medical follow-up and increase the chances of a normal delivery of a healthy baby.
Today, many unenlightened people mistakenly believe that pregnancy can be determined by performing an ultrasound scan. In reality, this is not the case. The main task of ultrasound is to assess the state of the embryo. Experts are trying to find out with what gestational age the real size of the fetus is comparable, based on the estimated period, calculated directly from conception or the beginning of the last menstrual bleeding. Ultrasound is prescribed at least 3 times to assess the dynamics of development and growth of the fetus in accordance with the gestational age.
For example, it was previously found out that the period is 32 weeks, and the ultrasound examination showed such dimensions of the fetus, which are inherent only in a 29-week-old embryo. In this case, doctors will not adjust the period according to the size, but conclude that there is a developmental delay of 3 weeks, and this implies a detailed examination and determination of the cause of the deviations.
In many cases, the pregnancy is proceeding normally, and an ultrasound scan reveals the correspondence between the size of the fetus's body and the established period. This fact gives rise to a false statement that an ultrasound examination is a way to determine the duration of pregnancy.
Based on the above information, we can conclude that it is really important for expectant mothers to know how obstetric weeks of pregnancy are counted. Experts emphasize that the correct gestational age in weeks can be established by examining the totality of data, which includes the following indicators: fetal growth dynamics, the onset of the last menstrual bleeding, the results of several ultrasound examinations and the date of conception.