A screening test is carried out once in each trimester. How many weeks 3 screening needs to be done, the doctor will explain in detail. The main thing is to have time to conduct an ultrasound examination from the 32nd to the 36th week. At the last ultrasound, the condition and position of the fetus is finally determined (by this time the fetus should occupy a longitudinal position with head presentation).
What examinations includes screening for the 3rd trimester
The last screening consists of several procedures. For all pregnant women, only an ultrasound scan is mandatory, the rest of the procedures and examinations are performed as directed by the doctor. The range of possible diagnostics includes:
- Dopplerography - 3 screening during pregnancy focuses on the correct location of the fetus and the stage of maturation of the placenta (during this period it should be at the 2nd stage of maturation).
- CTG - cardiotocography (a study of the heart rate of the fetus).
- Biochemical analysis of blood (triple - with the determination of total hCG, PAPP-A and ɑ-fetoprotein).
Biochemical analysis is prescribed only for certain indications. In the last trimester, unlike the first, it is necessary to conduct a triple test instead of a double one in order to more fully assess the development of the fetus.
Why do ultrasound in the 3rd trimester
At how many weeks 3 screening needs to be done, each doctor determines individually. It depends on many indicators. At the latest ultrasound, much attention is paid to the following characteristics:
- The state of the cardiovascular system, the presence of heart disease or other pathologies localized in this area.
- Since the brain is rapidly expanding and developing in recent weeks, special attention is paid to the study of this organ by ultrasound (in particular, the brain and the medulla oblongata).
- The vein of Galen, which is located in the cranial cavity and carries an important function for the normal functioning of the adjacent organs, is carefully studied.
- The state of the face is evaluated - especially the nasolabial triangle, upper lip and orbits. Terms 3 screening allow you to accurately determine the correct development of the facial region of the fetus and exclude any pathology.
- The correct development and condition of the spine, abdominal organs, and genitourinary system is important.
- Diagnosed with amniotic fluid, umbilical cord and placenta (its thickness, localization and degree of maturity).
- The genitals of the mother are also examined: the uterus and appendages.
In addition to these indicators, the doctor evaluates the features of the location of the fetus in the uterus, the presence of cord entanglement and presentation of the fetus. When entwining the neck with an umbilical cord, an additional ultrasound scan may be required after a week or two to see if the fetus has changed and the entanglement has been eliminated. In some cases, caesarean section may be required.
Dopplerometry
Dopplerometry is a study of the characteristics of blood flow in the umbilical cord, vessels of the uterus and fetus. It is necessary for determining the characteristics of the blood flow, it allows you to detect a lack of oxygen, the presence of pathologies of the central nervous system or the cardiovascular system.
How many weeks can 3 ultrasound screening and dopplerometry be performed? As a rule, in the presence of a suitable apparatus, which makes it possible to diagnose the features of blood flow, these studies are carried out simultaneously. Therefore, if it is necessary to conduct Dopplerometry, the gynecologist will send to the laboratory where two examinations are possible at once. In addition, this approach will significantly save money.
Cardiotocography
CTG is performed to determine possible fetal hypoxia. Allows you to determine the number of heartbeats of a child at rest and with motor activity. How is this type of screening done? The examination is similar to ultrasound, the only difference is that with CTG the fetus and its blood flow are not visualized, and only the features of the heartbeat are projected on the screen - slowing down or increasing (depending on the tests performed).
At screening 3, it is possible to determine the degree of maturity of the lung tissue and the readiness of the child for birth. If poor results are found, hospitalization of the pregnant woman and, in some cases, early delivery may be required in order to preserve the life and health of the mother and child.
How do screening: features of CTG
If everything is clear with the features of ultrasound, the technique of cardiotocography raises many questions in pregnant women. The examination consists in the use of an ultrasonic sensor; it can be convex or flat. The sensor is fixed on the pregnant woman’s stomach with a soft strap in the place where the fetal heartbeat is best heard.
A woman at this time is given a special remote control, on which she will need to be pressed at the time of fetal movement. The procedure takes an average of 40 minutes. If necessary, the doctor may recommend causing fetal movements by irritating the abdominal wall or by eating a piece of chocolate.
If it is not possible to cause fetal movements by such methods, the doctor may resort to the introduction of special medications into the vein, with the help of which the drug will show if the fetus has hypoxia.
Blood chemistry
In addition to the above examinations, a biochemical blood test is also necessary, which includes 3 screening. What does this analysis look like? In addition to standard indicators of total hCG and PAPP-A, a survey of indicators of free estriol and placental lactogen is mandatory .
All indicators should normally be in the range of 0.5-2 MoM. If measurements are made in other units, then the laboratory will indicate the norms in another column. Since each laboratory has its own characteristics of calculating normal indicators of pregnancy hormones in the blood.
These indicators indicate the normal development of the fetus, if their concentration is within normal limits. Most often, blood biochemistry is prescribed only if there are bad tests that were done in the second trimester of pregnancy.
3rd Screening Dates
"When to do 3 screening?" - a question that only the attending physician can answer. The final timing of the examination depends on the individual characteristics and indicators of the pregnant woman.
Most often, an ultrasound scan is performed on the 32-34th week, after which, with the results obtained, it is necessary to go to blood biochemistry. CTG and Dopplerography can be started already from the 28th week, especially if there is a special doctor’s testimony for this.
Timely examination eliminates the possibility of fetal hypoxia and other dangerous changes in its development.
What preparation includes 3 screening
What doctors look at greatly affects the characteristics of the preparation of the pregnant woman. So, ultrasound, CT scan and Dopplerometry does not require prior preparation. While a blood test requires a certain diet. The list of prohibited products includes:
- fatty and fried foods;
- spicy and salty dishes;
- smoked meats;
- chocolate.
It is also worth recalling that immediately before the test, you must withstand a 4-hour break in food intake. A diet is necessary to maintain a normal state of blood plasma, since when eating fatty foods, fat drops are deposited in it, which distort the results, and in some cases make diagnosis impossible.
Third Screening Standards
Decoding 3 screening requires care from doctors. In the third trimester, there are certain indicators and their norms. The main ones are:
- The thickness of the placenta. Normally, for a period of 32-34 weeks, the thickness varies between 25-43 mm.
- The degree of maturity of the placenta. At the 32nd week, the placenta is at the 1st or 2nd degree of maturation.
- Amniotic Water Index. Fluctuates within 80-280 mm.
- The internal pharynx of the cervix should be closed, and its length should be at least 3 cm.
- The tone of the uterus should normally be absent. Otherwise, there is a likelihood of premature birth or placental abruption.
- The weight of the fetus is within 2 kg, and the growth is 45 cm, normal anomalies and developmental pathologies are absent.
Only the doctor who initially leads the pregnancy and knows all the nuances of its course can correctly decipher the results of the examination. "What is the optimal time for 3 weeks of screening?" - This is a question that depends on many individual factors.