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Ultrasound examinations are recognized as the best methods for examining the course of pregnancy at any stage, due to their information content and complete safety for the woman and the fetus. With the help of ultrasound, it is possible to detect pregnancy in the early stages (about the fifth week), as well as to visualize the formation of the fetal egg at the fifth week, and the emergence of the embryo at the sixth.
It is necessary to undergo ultrasound during pregnancy three times – between 10 and 14 weeks, 20 and 24 weeks and 30 and 34 weeks. Gynecologists recommend that all women adhere to this schedule and not abuse this procedure, heading for it only according to indications and strictly according to the doctor’s prescription.
Types and purposes of ultrasound in the first trimester
Ultrasound during pregnancy can be transabdominal or transvaginal. In the case of transabdominal ultrasound, a pregnant woman should drink about half a liter of ordinary table water half an hour before the procedure and then do not go to the toilet. To make the study possible, it must be carried out with a full bladder. There is no need to prepare for transvaginal ultrasound in advance; it is better to empty the bladder on the eve of the procedure. Such an ultrasound is performed by inserting a special sensor into the vagina.
The duration of any ultrasound examination during pregnancy in the 1st trimester cannot exceed half an hour, which is usually enough to record all the measurements necessary for the doctor and enter this information into a special protocol that helps the future gynecologist who observes the patient to draw the right conclusions about the condition of the woman herself and the development of the fetus .
Ultrasound of the first trimester should be performed by all pregnant women in order to identify the location of the fetal egg, in order to avoid the occurrence of an ectopic pregnancy, diagnose pregnancy with multiple fetuses, assess the development of the embryo and the size of the fetal egg, as well as to identify abnormalities in the course of the condition – the presence of uterine tone, the threat of spontaneous abortion and other things.
Also, when conducting ultrasound, it becomes possible to diagnose all kinds of internal diseases of the genital organs – uterine myoma, ovarian tumors, intrauterine septum, uterine bicornuity.
Indicators of ultrasound of pregnancy in the first trimester
When conducting an ultrasound examination of pregnancy in the first trimester, the diagnostician should observe a rounded darkening in the upper part of the uterus, which means the presence of a fetal egg. In the event of a multiple pregnancy, there will be several such spots, which will allow us to conclude that twins are conceived.
With transabdominal ultrasound, a normal intrauterine pregnancy can be diagnosed as early as the 5th week after conception, with a delay in the menstrual cycle for a period of about 2 weeks from the expected date of occurrence.
At the fifth week, the fetal egg has a diameter of about 5 millimeters. With transvaginal diagnosis, it becomes possible to see the emerging life as early as 4 weeks, on the sixth day, with a delay in the onset of planned menstruation. In this case, the norm for the size of the fetal egg will be an indicator of 3 millimeters.
In order to make it possible to visually verify the presence and health of the embryo, transabdominal ultrasound should be done no earlier than the sixth week, and transvaginal one a week earlier. The appearance of the embryo is a light spot inside a dark one, which means a fetal egg in the diagnosis. To listen to the fetal heartbeat, any type of ultrasound in the first trimester must be performed no earlier than 6 weeks of pregnancy.
As a rule, with a regular menstrual cycle, it is possible to perform a transvaginal ultrasound at six weeks of the expected pregnancy, but this is not necessary. With regular failures in menstruation, gynecologists rely on diagnosticians to set the exact timing of the conception of the fetus.
Diagnostic evaluation of the embryo and ovum
To diagnose the normal development of the fetal egg and embryo during pregnancy, experts use 2 main indicators that characterize these structures:
- coccygeal-parietal dimensions;
- fetal egg in the context of the inner average diameter.
In the software of devices designed for ultrasound examination of pregnancies, there are built-in parameters for the relative norm of certain indicators, including the average internal diameter of the fetal egg.
According to these parameters, the program determines the timing of pregnancy with high accuracy. Errors in setting deadlines are 6 days in any direction.
The coccygeal-parietal dimensions determine the length of the visualized embryo from the head to the level of the coccyx. This size becomes available for visualization before other parameters of the baby’s nascent body. It is according to these indicators that it is easy to clarify the timing of conception with an error of only 3 days.
It is important to remember that when visualizing a fetal egg with dimensions reaching 14 millimeters, and the absence of visualization of the embryo, experts talk about stopping the development of pregnancy. In the presence of an embryo, doctors pay special attention to its motor activity and heartbeat. According to these indicators, the viability of the fetus is assessed.
With transvaginal ultrasound, the heartbeat is noticeable as early as the sixth week. With its normal indicators, a high-precision rhythm in contractions is noted, and the frequency indicators may vary, depending on the gestational age:
- until the eighth week they should be about 130-140;
- until the tenth week, the rate will be 190 beats per minute;
- after the tenth week and until childbirth, the heartbeat should be 140-160 beats per minute.
It is the indicator of the heart rate that demonstrates to specialists the presence or absence of problems with the bearing of the fetus, therefore this parameter is always subject to mandatory registration. With a sharp excess or decrease in the heart rate of the embryo, a woman is at risk of miscarriage. At the same time, if the length of the embryo is visualized in the region of 8 millimeters, and the heartbeat cannot be determined, a second ultrasound is performed after 7 days and after that a decision is made to make a diagnosis of “non-developing pregnancy”.
In terms of the motor activity of the embryo, which occurs and is visualized at 7-9 weeks of pregnancy, doctors do not make any special conclusions about the viability of the embryo, since along with the chaotic movements of the whole body, and later with its clear flexion-extension, there are unpredictable and long-term periods of rest and rest. That is why, on ultrasound, embryos are often completely motionless, but at the same time, experts do not find anomalies in the development of pregnancy.
Also, a very important aspect of ultrasound examination of pregnancy in the first trimester is the assessment of the anatomy or structure of the fetus.
At a period of 12 weeks, numerous possible pathological anomalies of the structure are clearly visible, which in the future will not be compatible with the life of the child. Such anomalies include the absence of a brain, anomalies in the development of the skeleton, a hernia of the spinal cord, and so on.
On ultrasound, it is important to assess the collar space, since in terms of its thickness, conclusions can be drawn about the presence of chromosomal diseases in the fetus. Exceeding the set value by 3 millimeters is the norm, and with a higher indicator, a conclusion is made about the likelihood of chromosomal pathology in 80% of cases.
Modern ultrasound equipment allows specialists to diagnose with high accuracy all anomalies in the development of the fetus already at a period of 12 weeks, which allows future parents to independently decide whether to continue the pregnancy or terminate it for medical reasons.
Extraembryonic structures and their characteristics
There are also some extraembryonic structures that must be studied using ultrasound in the first trimester of any pregnancy. These include the yolk sac, chorion and amnion.
Throughout pregnancy, nutritional and hematopoietic functions will be performed by the yolk sac. It begins to be visualized at 5 weeks, at 10 weeks it begins to reach a size of 7 millimeters, but after the 12th week it becomes impossible to normally identify or assess the condition and size of the yolk sac.
At the same time, there is a direct relationship between the size of the yolk sac, its shape and walls with the development of the embryo – if the parameters of the yolk sac are violated, specialists can draw conclusions about violations of the course of pregnancy in general.
The hairy membrane of the fetal egg is called the chorion. In the first trimester of pregnancy, the thickness of the chorion is usually equal to the very period of gestation in weeks. With changes in the structure of the chorion, specialists can predict dangers to the viability of the embryo. When the structure of this shell changes, the villi, with the help of which the chorion is attached to the walls of the uterus, cease to fix the fetal egg, and the process of miscarriage begins.
The water sac where the embryo is located in the fetal egg is called the amnion. Amnion must be studied in the early periods of bearing a child to determine the absence or presence of pathologies in the diameter of the amniotic cavity.
With a small amnion size, pregnancy will have difficulties in its own development, and with a large one, experts will conclude that intrauterine infectious processes have occurred.
Identification of complications on ultrasound
Diagnosis of the first trimester of pregnancy is almost entirely carried out in order to prevent the interruption of childbearing. It is ultrasound that will help specialists to examine the thickened walls of the uterus of a pregnant woman, which will be evidence of the onset of a miscarriage.
Such hypertonicity of the myometrium is usually always accompanied by pain in the lower abdomen, which leads women to ultrasound at the earliest possible date.
With early detection of hypertension, drug treatment is possible, which should lead to the preservation of pregnancy.
However, this does not apply to cases of the onset of spontaneous abortion with bloody discharge, when the detachment of the fetal egg is visualized on ultrasound. At the same time, ultrasound is necessarily performed again to determine the remnants of particles of the ovum in the uterine cavity, so that, if any, send the patient for curettage in order to prevent the occurrence of foci of intrauterine infection.
With the help of ultrasound examination of early pregnancy, doctors can also diagnose corpus luteum cysts, which are quite common and are capable of self-resolving by the end of the first trimester of pregnancy, and hydatidiform drifts, which are rare complications with pathological lesions of the chorion. With cystic drifts, fetal death always occurs.
Also, ultrasound of the early stages of pregnancy helps to determine any type of pathology in the fetus. So, at week 12, doctors can see the baby’s cleft lip and other facial malformations.
The main difficulty in this case is that ultrasound can be performed on women only at their personal request, which does not allow in 100% of cases to identify malformations and make an adequate decision on the advisability of maintaining the current pregnancy.