The first time the ultrasound is done during the first visit of a woman to the doctor immediately after she learns the good news. In the early stages (5−6 weeks), the main goal of the study is to determine if it is a uterine pregnancy or ectopic.
The next time a mandatory ultrasound is carried out for a period of 10 to 13 weeks. If a woman finds out that she is pregnant during this period of time, then the second scheduled examination becomes the first in a row.
This time we are talking about ultrasound screening – a study that allows you to identify the risk of developing defects in the baby. At this stage, it is possible to identify 2 congenital chromosomal diseases – Down and Edwards syndromes.
For the next 7 days, and ideally on the same day, for the accuracy of the results, the expectant mother should undergo a biochemical screening, the so-called “double test”. To do this, you will need to donate blood from a vein.
If the results of these two studies reveal a high risk of malformations in a child, the doctor will recommend invasive prenatal diagnosis in order to analyze the chromosome set of the child and clarify the diagnosis.
The second ultrasound screening occurs on the 20th to 22nd week. His results are also summarized with the results of biochemical screening (this time it is called the “triple test”: in addition to Down and Edwards syndromes, it allows you to detect the third chromosomal disorder – a neural tube defect that is done for a period of 16 to 21 weeks.
The last planned ultrasound is performed on the 32nd week. It is also aimed at detecting possible defects that could not be identified at earlier periods due to the fact that the baby was still too small.
During ultrasound examinations, doctors evaluate a variety of parameters that should correspond to a given gestational age: the size of the uterus and baby, the tonus of the myometrium, the degree of maturity of the placenta, the quantity of amniotic fluid are evaluated. Analyze the structure of the internal organs of the baby, the position of the umbilical cord.
Deviations from the norm can talk about the threat of termination of pregnancy, problems with gestation, possible complications during and after childbirth.
This method of ultrasound diagnostics allows you to find out if the baby is getting enough nutrients and oxygen from the mother or not. To do this, during the examination, doctors evaluate the characteristics of blood flow in the uterine artery, umbilical artery and the middle cerebral artery of the child.
Having found out with what speed the blood flows through the vessels, it can be concluded how quickly and in what quantities the nutrients and oxygen are supplied to the baby and whether these figures correspond to the gestational age.
The study is conducted in 2 stages. First, the doctor finds each of the three arteries using an ultrasound machine.
When her image appears on the screen, the doctor turns on a special sensor (doppler) that measures the speed of blood flow, its pressure and vessel resistance.
Depending on what kind of blood flow disturbances dopplerometry revealed, it can be assumed what complications will arise during pregnancy. So, if the baby does not have enough nutrients, it can be born low in weight, and when it does not receive enough oxygen, it develops hypoxia.
According to the doctor, for example, if there were complications during previous pregnancies, dopplerometry can be performed from the 13th week. In the general practice and without fail, this examination is prescribed to every pregnant woman from the 22nd to the 24th week.
If the doctor reveals a violation, he will prescribe a re-examination.
The study is to assess two parameters – the baby’s heart rate and the state of uterine tone. They are measured by 2 sensors that are attached to the expectant mother on the stomach.
She holds the third in her hand, pressing the button every time the baby moves. The essence of the method is to analyze the change in the child’s heartbeat in response to his own movements.
The goal is to find out if there is enough oxygen to the baby.
How does this method work? When we move, our heartbeat quickens.
This phenomenon is called the cardiac reflex, which is formed during fetal development, as a rule, by the 30th week of pregnancy. If we do not have enough oxygen, the heartbeat will increase more than usual and the number of beats per minute will exceed the norm. The same changes can be traced to the baby.
However, if he has experienced oxygen starvation for a long time, his body will behave differently. Saving strength, the baby will move less, and in response to the movement of his pulse will not increase, but rather slow down.
However, in both cases, the diagnosis is one: fetal hypoxia, only of varying degrees.
As a rule, during pregnancy, the second sensor, assessing the tone of the uterus, is rarely used. But during childbirth, it is irreplaceable, because it shows how often the contractions take place, what is their strength and duration. If they are weak, special preparations will be required to strengthen them.
Watching the baby’s heartbeat changes, doctors can notice a number of other complications in time. So, if they notice that the child does not have enough oxygen, it is possible that he will not be able to withstand natural childbirth, and then he will have to do a caesarean section.
CTG must be done at least once, at the 34th week. However, many obstetrician-gynecologists advise all women to undergo this study at intervals of 10–14 days from the 30th week, once the baby has a cardiac reflex.
The sooner the child has hypoxia, the more time will be left for treatment.