Ultrasound, or ultrasound examination, is a method of examination that is widely used in all branches of medicine, including obstetrics and gynecology. Ultrasound is the safest and most cost-effective method for diagnosing pregnancy, as well as for detecting various abnormalities in fetal development.
On the ultrasound machine's monitor the image is in motion, which makes it possible to see the fetal heartbeat and its movements. Using ultrasound, the doctor measures fetal parameters that indicate the gestational age and also make it possible to monitor the normal development of the fetus.
How is an ultrasound performed?
There are several ways to perform an ultrasound during pregnancy: through the skin of the front wall of the abdomen, and also transvaginally (the ultrasound probe is inserted into the vagina).
When the ultrasound is performed through the skin of the abdomen, a thin layer of special gel is applied to the skin surface before the probe is placed on it; the gel helps the ultrasound waves penetrate into the abdominal cavity as well as possible.
What does a woman feel during an ultrasound?
During an ultrasound, a woman does not feel the sound waves coming from the probe. Ultrasound is completely painless.
As a rule, for an ultrasound in early pregnancy, a woman is advised to fill her bladder, which causes some discomfort when the probe presses on the lower abdomen. In addition, a mandatory condition for the ultrasound is applying a special gel to the skin over the area being examined, which may feel cold and "wet" to the woman. However, this is where the unpleasant sensations associated with ultrasound end.
How harmful is ultrasound during pregnancy?
The safety of ultrasound during pregnancy is a fundamental question that determines how widely ultrasound is used among pregnant women. Numerous clinical studies that examined the effect of ultrasound on the course of pregnancy have proven that ultrasound is absolutely safe for the fetus. Despite this, most expectant young mothers fear possible harm from ultrasound to their future baby, equate ultrasound with other hazardous diagnostic methods, and avoid even the recommended ultrasound sessions.
Ultrasound is safe because:
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No radioactive rays are emitted during an ultrasound session.
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Ultrasound waves are very high-frequency sound vibrations carrying very little energy, which cannot damage the baby's tissues even with very prolonged exposure.
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Ultrasound cannot cause any fetal malformations, but it can help detect them in time.
Why is ultrasound used during pregnancy?
Ultrasound is the most accessible and safe method of examination, which is used in obstetrics and gynecology for the following purposes:
Diagnosis and confirmation of pregnancy at an early stage.
The first signs of pregnancy can be detected by ultrasound when the diameter of the gestational sac (the embryo together with its membranes) reaches only 2-3 mm, which corresponds to approximately ,5 weeks of pregnancy. The embryo itself becomes visible at approximately ,5 weeks of pregnancy. During early diagnosis of pregnancy by ultrasound, an important point is identifying where the gestational sac is attached; it must be located in the uterine cavity. The presence of a gestational sac outside the uterus (in the fallopian tube, the cervix, the abdominal cavity) is called an ectopic pregnancy and requires immediate treatment (termination of the ectopic pregnancy).
In addition, ultrasound can reveal a multiple pregnancy.
Assessment of fetal viability.
If bloody discharge from the genital tract appears in early pregnancy, ultrasound makes it possible to determine whether the fetus is viable or to diagnose fetal death.
An important point in assessing fetal viability is examining the fetal heartbeat. The fetal heart begins to beat at 5 weeks of pregnancy and can be detected on ultrasound from approximately 7 weeks of pregnancy. Thus, if no fetal heartbeat is detected at 7 weeks, intrauterine fetal death (missed miscarriage) is likely. The fetal heart rate is also taken into account when assessing fetal viability: normally, at 6 weeks of pregnancy the fetal heart beats at a rate of 90 - 110 beats per minute. A slowing of the fetal heart rate to less than 90 beats per minute very likely indicates that the fetus is not viable and that there is a risk of pregnancy loss.
Determining gestational age and fetal size.
Determining gestational age by ultrasound is indicated for women with an irregular menstrual cycle who do not know the exact date the baby was conceived. In most cases, the gestational age determined by ultrasound corresponds to the time elapsed since the first day of the last menstrual period. Measuring fetal size makes it possible to monitor intrauterine development, and it is also an important method for diagnosing fetal growth restriction and "missed miscarriage."
The following parameters are important when measuring fetal size:
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Crown-rump length of the fetus - measured from 7 weeks of pregnancy and gives an accurate idea of the actual gestational age. Gestational age is calculated from the length of the fetus using special tables.
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Biparietal diameter is the distance between the parietal bones of the fetal head. The biparietal diameter is measured after-12 weeks of pregnancy and is an important indicator of gestational age in the second half of pregnancy.
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Fetal femur length – the longest bone of the body is measured, which reflects how much the fetus has grown in length.
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Fetal abdominal circumference – indicates the size and estimated weight of the fetus.
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Fetal head circumference is also used to determine gestational age and whether the baby can be born naturally. In the last week of pregnancy, a special ultrasound session is usually performed, during which the doctor determines the size of the inlet of the woman's pelvis and the size of the baby's head. If the size of the baby's head exceeds the size of the pelvis, a cesarean section is performed.
Determining the baby's sex.
Ultrasound diagnosis makes it possible to determine the baby's sex even before birth. Usually the baby's sex characteristics become distinguishable after 20 weeks of pregnancy and are determined during the second routine ultrasound. According to various estimates, the accuracy of determining the baby's sex by ultrasound reaches 80-90%.
If you do not want to know the baby's sex before birth, you must be sure to tell the doctor before the ultrasound session begins, as the doctor may share this news without asking.
Determining the baby's sex is important not only to satisfy the curiosity of some parents, but it also helps address some serious problems. For example, determining the sex makes it possible to assess the risk of the baby being born with a certain congenital disease that affects only boys (for example, hemophilia) and to prepare to start treating the baby immediately after birth.
Diagnosis of fetal developmental abnormalities.
Ultrasound diagnosis at early stages can detect many structural fetal developmental abnormalities, which makes it possible to raise the question of whether continuing the pregnancy is advisable or whether the baby needs treatment even before birth. For example, ultrasound can detect hydrocephalus (water on the brain, or accumulation of a large amount of cerebrospinal fluid in the cranial cavity), anencephaly (absence of the brain), myelomeningocele (a hernia of the spinal cord), spina bifida (a serious malformation of the spine), closure (atresia) of the duodenum, heart defects, and many others.
In the first trimester of pregnancy, ultrasound can raise suspicion of a serious genetic defect in the fetus called Down syndrome: it has been established that a fetus with Down syndrome has an underdeveloped nasal bone and also swelling on the back of the neck (thickening of the nuchal fold). The presence of ultrasound signs of Down syndrome in the fetus is an indication for further tests (for example, amniocentesis - examination of the fetal amniotic fluid), which confirm or rule out Down syndrome.
Determining where the placenta is attached.
The placenta, or afterbirth, is the organ through which the fetus receives its blood supply and nutrition. Ultrasound detects abnormalities in the position and development of the placenta, for example placenta previa (the placenta lying too low in relation to the cervix, which leads to blocking of the exit from the uterine cavity during labor).
Determining the amount of amniotic fluid.
Amniotic fluid is the fluid surrounding the fetus, in which the baby is immersed. An increase in the amount of amniotic fluid (hydramnios) or a decrease in it (oligohydramnios) may indicate certain abnormalities in fetal development.
Use of ultrasound for other diagnostic procedures.
Amniocentesis is an examination of the fetal amniotic fluid that makes it possible to detect certain diseases (including Down syndrome). Amniocentesis is performed with a long needle, which is inserted through the front abdominal wall into the amniotic sac under ultrasound guidance.
Cordocentesis is the taking of blood from the fetal umbilical cord with a needle, which is inserted through the front abdominal wall under ultrasound guidance.
Assessment of the fetal biophysical profile.
The fetal biophysical profile is an ultrasound examination of the fetus that makes it possible to determine its condition in the womb. When determining the biophysical profile, the following are taken into account: fetal breathing movements, tone, movements of individual parts of the fetal body, fetal reactivity, and the amount of amniotic fluid.
Thus, ultrasound is an essential tool for monitoring the course of pregnancy, which makes it possible to assess all the important parameters of fetal development. Ultrasound diagnosis during pregnancy is a guarantee of the health of mother and baby.
Recommended timing of ultrasound during pregnancy.
During pregnancy it is recommended to have at least 3 routine ultrasound examinations of the developing fetus.
The first ultrasound in pregnancy is recommended at 12 to 14 weeks (on average 13 weeks). At this stage of pregnancy, the gestational age is assessed, certain developmental defects are looked for, and signs of Down syndrome in the fetus are identified. At 12 weeks of pregnancy it is possible to examine in detail the structures of the fetal brain, the size of the brain ventricles, the structure of the spine, as well as the fetus's arms and legs and its internal organs. At 12 weeks the fetus is still too small to detect most malformations; therefore, the main goal of ultrasound at this stage is to determine the level of risk of the baby being born with Down syndrome (indicated by absence of the fetal nasal bone and thickening of the nuchal fold). It should be understood that the presence of ultrasound signs of Down syndrome does not mean that this condition is 100% present, and therefore other, more informative diagnostic methods in this area need to be carried out (amniocentesis, etc.)
The second ultrasound is recommended at 20 to 24 weeks of pregnancy (on average 22 weeks). By 22 weeks of pregnancy the fetus is large enough for ultrasound to detect malformations. Among other things, at the 22-week pregnancy ultrasound it is important to detect delayed fetal development, abnormal placental position (placenta previa), and the amount of amniotic fluid. At 24 weeks of pregnancy the fetal heart is fully formed, which makes it possible to determine the presence of heart defects with greater accuracy.
The third ultrasound during pregnancy is recommended at-34 weeks. At this stage, ultrasound helps determine the degree of fetal development, as well as some malformations that were not detected at earlier stages. The amount of amniotic fluid, the location of the placenta, etc. are assessed.
It is important to understand that if there are certain symptoms indicating a possible pathology (abnormal course) of pregnancy, a woman may need to have more than three ultrasound examinations. The most common indications for additional ultrasounds in pregnant women are:
- Bloody discharge from the genital tract.
- Pulling pain in the lower abdomen.
- Abnormal placental attachment.
- Fetal size not matching the expected gestational age (fetal growth restriction).
- Suspected pregnancy loss.
Remember! Changing the timing of the ultrasound examination reduces its effectiveness.
Why and at what stage of pregnancy is Doppler ultrasound performed?
Doppler ultrasound is an examination of blood flow parameters in vessels. In obstetric practice, the vessels of the fetus, uterus, and placenta are examined. Based on the data obtained, a conclusion is made about the functional condition of the fetus. This examination is usually performed in the third trimester of pregnancy, but sometimes earlier.
Doppler ultrasound is prescribed by the doctor monitoring your pregnancy, or by the ultrasound doctor during the examination when they see a need for it.
Doppler ultrasound during pregnancy is performed when indicated!
It is better to perform this examination after 20 weeks of pregnancy (preferably at 26-28 weeks), and if necessary it is performed– as many times as needed, right up to delivery.
In which cases is an additional Doppler examination indicated?
Indications for an additional Doppler examination may include certain diseases of the pregnant woman (kidney disease, hypertension, diabetes) or pregnancy complications (late toxicosis, Rh incompatibility, polyhydramnios or oligohydramnios). In addition, a Doppler examination is prescribed if congenital fetal malformations are suspected that cannot be detected in early pregnancy – for example, congenital heart defects or a fetus not matching the gestational age. Doppler examination determines the speed and direction of the flow of fluids circulating in the baby's body.
Doppler examination during pregnancy helps assess the condition of the fetal circulatory system: the degree of blood flow in the main vessels, as well as the work of the fetal heart. Doppler examination of blood flow in the fetal umbilical vessels makes it possible to determine the cause of low fetal weight (reduced blood supply to the fetus is the cause of a low-birth-weight baby).
Is Doppler ultrasound dangerous for the health of the fetus and mother?
Currently, WHO recommends performing ultrasound four times during pregnancy. Meanwhile, many expectant mothers fear that ultrasound, being essentially a form of irradiation, harms the fetus. Although scientists have so far not recorded any harmful effects of ultrasound on the physical and neuropsychological development of the fetus or the condition of the expectant mother, opponents of ultrasound believe that the studies carried out are insufficient and that the harmlessness of these procedures has not been fully proven.
Modern prenatal diagnosis uses probes with an emission frequency that is safe for humans; the ultrasound lasts only a few minutes, and most of the ultrasound energy does not reach the fetus, being reflected by and absorbed into other organs. In addition, the machines used for the examination operate in pulse mode, with a pulse duration of no more than 1 microsecond and an interval between pulses of 1 millisecond, which means the actual emission lasts no more than one thousandth of the total examination time. Nevertheless, scientists confirm that in the first weeks of development the embryo is more sensitive to high-frequency ultrasound than a mature fetus, and therefore do not recommend undergoing a Doppler examination in early pregnancy without special indications, since this examination uses a higher level of ultrasound emission than a regular ultrasound.
Three-dimensional (3D) and four-dimensional (4D) ultrasound during pregnancy.
Three-dimensional ultrasound is a newer method of examination that makes it possible to see a "photograph" of the unborn baby on the monitor. With 3D ultrasound, the doctor can detect malformations of the fetal facial skeleton and abnormalities such as cleft lip, an increased number of fingers and toes on the fetus's hands and feet, etc. Four-dimensional fetal ultrasound is an even more complex and advanced method of examination that makes it possible to observe a three-dimensional image of the baby in motion. Thus, 3D ultrasound can be compared to a photograph, and 4D ultrasound to video recording. It is not fair to say that 3D and 4D ultrasound are more informative than ordinary, classic 2D ultrasound, since all these methods are used for different purposes. For example, classic ultrasound can detect those fetal malformations that are not visible on 3D ultrasound.
The first ultrasound examination does not allow a full assessment of anatomy or diagnosis of malformations because of the small size of the fetus. The optimal time for assessing fetal anatomy on ultrasound is 21-24 weeks.
The second ultrasound of the fetus and pregnant woman (21-24 weeks) is necessary to assess fetal anatomy and rule out congenital malformations that can be detected by ultrasound. The interval from 21 to 24 weeks is optimal for visualization (visual detection) of fetal structures on ultrasound. Earlier and later in pregnancy, many fetal structures are poorly visible on ultrasound, which creates the conditions for some malformations to be missed.
Remember! Unfortunately, the laws of prenatal fetal formation are such that not all developmental abnormalities can be detected by ultrasound examination in the prenatal period, even in the 21-24 week interval. In addition to assessing fetal anatomy on ultrasound, in the 21-24 week interval it is possible to assess blood flow in the uterine arteries and umbilical cord arteries in order to predict the development of various complications later in pregnancy.
The third fetal ultrasound during pregnancy (32-34 weeks) is necessary to detect those malformations that manifest only late in pregnancy. In addition, in the 32-34 week interval, additional examinations (Doppler ultrasound, cardiotocography) are performed to assess the condition of the fetus in the womb and to predict certain complications in the prenatal period and during labor.
