Ultrasound at 21 weeks of gestation: fetal size and other features

The first half of the pregnancy is over. Week 21 opens the second half of this interesting and difficult period, filled with hopes and new feelings. At this time, a study may be assigned as part of the second screening.

The purpose of the survey

The second prenatal screening, or rather, one of its components - an ultrasound examination, is carried out on any of the days between 18 and 21 weeks of pregnancy. Laboratory blood tests for hormones and proteins, the so-called triple test, are taken earlier - from 16 to 20 weeks. Thus, at 21 weeks, all pregnant women who did not have time to undergo this examination in the previous three weeks will be sent for an ultrasound scan.

Purpose of the study - identify the risks of possible genetic abnormalities in the fetus. Ultrasound diagnostics in this process has a special role, its results significantly affect the overall conclusion.

In addition, at 21 weeks, the expectant mother can visit the ultrasound office for other reasons. The appearance of a pain syndrome, abnormal discharge for the duration of the discharge, ichor, signs of inflammation, the emergence of a threat to maintain pregnancy - all this is the basis for an urgent unscheduled diagnosis of the condition of the mother and fetus. An obstetrician-gynecologist may recommend an ultrasound scan if the height of the bottom of the uterus does not correspond to the obstetric term, if a woman complains that she suddenly stopped feeling fetal movements, although they used to be.

Sometimes it becomes necessary to clarify the timing of pregnancy and determine the date of the upcoming birth.

Preparation and features

At this time, the ultrasound examination procedure is transabdominal: the sensor is located on top of the abdomen, the uterus and the baby are viewed through the anterior abdominal wall. The specialist can use the vaginal sensor only if the view through the abdomen is difficult due to the excess weight of the pregnant woman, obesity, and also in cases where it is necessary to examine the cervix and cervical canal to assess the possible threat of termination of pregnancy at this time.

This ultrasound does not require specific preparation from a woman, no need to fill the bladder, since the amount of amniotic fluid is sufficient for good visualization, and intestinal gases, which had to be dealt with before ultrasound scanning in the first trimester, can no longer affect the examination result, because the uterus has grown, and it is no longer possible to squeeze it with a swollen intestine.

What is seen on an ultrasound scan?

The kid grew up and "took shape": his height has already approached 25 centimeters from the heels to the crown, and his weight has exceeded 350 grams. The smallest children at this time have a height of about 18 centimeters. A toddler with such parameters is clearly visible on any scanner device, even if this equipment does not belong to the category of modern innovative technology. 21 weeks by obstetric standards - about 19 weeks from the moment of conception. During this time, the child has learned a lot and is ready to demonstrate a lot to his mother and doctor, who will observe him through an ultrasonic sensor for several minutes.

The baby has perfectly mastered a variety of facial expressions, this will be especially noticeable if a 3D ultrasound is done. He sucks fists, plays with the umbilical cord. At this time, hair begins to grow on the baby's head, and the digestive system begins to work. On the day, the baby swallows about half a liter of amniotic fluid.

At 21 weeks, the baby learns to distinguish between tastes, since taste buds appear on his tongue at this time. The arms and legs are still moving somewhat chaotically, and on ultrasound it is easy to see, coordination of movements is a task for the near future. The child hears various sounds, during the procedure, he can increase his motor activity to respond to the doctor's unfamiliar voice, to the measured hum of the equipment.

21 weeks is a great time to find out your baby's gender. If before that the doctor spoke uncertainly about the sex of the baby or it was not possible to examine the genitals, right now the secret may become clear. The uterus is still quite free, and the baby is constantly changing its position in space.

It is possible that it is during the ultrasound that the baby will turn around so that his external genitals will be available for examination.

Decoding and norms

The doctor's conclusion about the performed ultrasound scan always begins with determining the number of children. In relation to each of them, the specialist sets the criteria for viability - the baby's heart should be beating and physical activity should be present. Also, the specialist determines the type of location of the child in the uterus - head, pelvic or transverse.

However, while a woman should not be upset by either the pelvic or transverse presentation, because it is still a long time before giving birth, the baby is constantly moving, and his position will change more than once.

Fetometry of the fetus

The obstetricians have a special attitude to fetometric data - the sizes of individual parts of the child's body allow one to get an idea of how proportionally it is complex, whether it grows and develops correctly. Such data include abbreviations already familiar to a woman - БПР, ЛЗР, ОГ and ОЖ:

Bipariental dimension - a visual segment drawn between the two temporal bones of the head,
The frontal-occipital size is a longitudinal segment from the frontal bone to the occipital bone.
Head circumference and abdominal circumference are two additional parameters to judge the development of a child.

The length of the paired bones - femur, lower leg, forearm and shoulder - are important signs of the successful growth of the baby, as well as markers of possible chromosomal abnormalities.

The table of average norms of fetometric indicators at 20-21 weeks is as follows:

The table of norms for the length of paired bones at week 21 is as follows:

The interhemispheric size of the baby's cerebellum at this time is close to 21-23 mm. The estimated weight of the crumbs is already in the range of 350-420 grams.

Anatomical features of the fetus

All internal organs of the child are fully formed. Most of them are running smoothly, some are just getting started. Ultrasound examines the hemispheres of the brain, the presence and features, if any, of the lungs, organs of the urinary system - the bladder and kidneys. The heart should have 4 chambers, beat rhythmically, evenly. Since the gastrointestinal tract begins to work actively at 21 weeks, the doctor carefully examines the stomach, intestines, gallbladder. The spine and bones of the face and skull are evaluated.

If no visible defects are found, the doctor does not delve into the details of the description of each examined organ and indicates that they are all normal and have no peculiarities. If a defect is found, the doctor describes in detail the type of pathology, the decision on additional diagnostics and possible treatment.

In this case, all decisions will be made by the obstetrician and pediatrician jointly.

Placenta, uterus, amniotic fluid

Zero maturity of the placenta is considered normal this week. This means that this temporary body, which is entrusted with important responsibilities - to provide the child with everything necessary, is young enough and successfully copes with its main task. If the doctor claims that the placenta is located low, do not worry, because the uterus has yet to grow, and along with the stretching uterine walls, the "child's place" can also "migrate".

However, low placentation leaves its mark on the daily life of the expectant mother - she needs to treat her pregnancy more reverently and carefully, take care of yourself, do not lift weights, do not make sudden movements, take vitamins and visit your doctor more often than other pregnant women, so that the control is constant. The amniotic fluid at 21 weeks should be clean, transparent, free from suspension. Their normal amount at this time is 143-214 mm.

The uterine walls should not be toned, the cervix should not undergo changes, the cervical canal is normally tightly closed.

Possible problems

There are several problems that can be detected on an ultrasound scan at this time.

Fetometric data differ from real term

A slight deviation of the individual sizes of the baby from the average norms may not indicate pathologies of fetal development. The reason may be heredity: the small stature of the parents is likely to be passed on to the child, and therefore one should not expect a large length of bones from him. If mom or dad has a big head, then the child may have the same, and therefore the head parameters by ultrasound will be slightly ahead of the normative data.

Such a deviation is considered alarming, in which the period according to the tables is "shifted" by 2 or more weeks. If at 21 weeks the size of the head (BPR and LZR) barely reaches 18-19 weeks, this is the basis for the appointment of additional diagnostics, since there can be many reasons for this - microcephaly, malformations, genetic pathologies, oxygen starvation, malnutrition of the fetus, developmental lag.

An increase in sizes by 2 or more weeks may also indicate possible problems in the future, but other sizes should also be estimated. If the increase is proportional, and other parameters are also ahead of the standards, then we can talk about a tendency to give birth to a large or giant child. If only certain parts of the body are enlarged, a detailed examination of the reasons for this phenomenon is required.

With pronounced asymmetry of the child's body parts, invasive diagnostics can be prescribed - amniocentesis or cordocentesis, which with a probability of 99.9% will answer the question if the child has gross malformations.

Low water or polyhydramnios

A small amount of water at 21 weeks, as well as too much water, can also be a sign of possible malformations. Some of the incurable chromosomal syndromes are indeed accompanied by oligohydramnios or polyhydramnios, but most often the reasons lie in other pathologies of pregnancy - inflammation of the genitourinary system, infectious diseases, Rh-conflict, and so on.

Any deviation in the amount of water from the norm is a threat primarily to the safety of the child, therefore you should not leave the identified violations to their fate.

Only with medical help is it possible to inform a child and in some cases even give birth to a child naturally, without a cesarean section.

Pictures

The ultrasound images at 21 weeks clearly show the baby's profile, the shape of the nose, jaw, and forehead. The outlines of the spine, costal arches, limbs are no less noticeable. The sex of the child, if the doctor manages to choose a good angle, can already be seen almost without a doubt.

In three-dimensional pictures, a baby can be captured with an interesting grimace, in such a first "photo" the baby's facial features are already visible, and parents can understand who their son or daughter looks like. The accuracy of sex determination and ultrasound diagnostics at this time is from 85 to 90%.