The timing of the second screening for pregnancy
Approximately 25-30 years ago in our country there was no such thing as a comprehensive examination of pregnant women. In the absence of a testimony, ultrasound was performed once for the entire term or not at all.
Modern medicine looks differently at conducting pregnancy, and according to world standards, prospective mothers are strongly recommended to undergo first and second screening. Ultrasound can help evaluate the development of the fetus.
The second trimester is called "golden period", which lasts from 14th to 27th week. The level of hormones in the blood gradually decreases, the body gets used to the changes. Morning sickness, nausea and excessive fatigue are giving up their positions, and pregnant women feel a surge of vitality.
Every two weeks, the expectant mother visits the attending physician who monitors the change in blood pressure and body weight, and also tracks the appearance of swelling. The blood and urine tests are mandatory.
Separately, the obstetrician-gynecologist tells about the timing of the second screening during pregnancy. Usually women are very nervous during these studies, but even with an unfavorable outcome, there is a probability of error. Screening rates are also given in our review.
A two-level system of antenatal research appeared relatively recently in Russia. A comprehensive examination is aimed at early detection of hereditary and congenital pathologies in the fetus.
The first stage is held for a period of 10-14 weeks. The results of 1 screening allow the formation of risk groups for some congenital malformations and chromosomal pathology. It is performed by ultrasound examination and blood analysis on PAPP-A and β-hCG. Additionally, the attending physician may prescribe a chorionic biopsy according to the following indications:
- an increase in the collar area of the fetus (from 3 mm);
- the age of a woman is 35 years old;
- chromosomal abnormalities in the family.
The timing of the second screening during pregnancy is 17-19 weeks. In the second trimester, the expectant mother will also have a diagnostic ultrasound and a blood test, often called a triple test.
The World Health Organization recommends conducting a second screening for all pregnant women and be sure to those at risk:
- age over 35 years;
- Two miscarriages and more;
- reception of contra-indicated to pregnant women in the first trimester;
- marriage between close relatives;
- prolonged threat of termination of pregnancy;
- pathology of fetal development on the first ultrasound;
Screening does not require special preparation. It is important to remember that after the twentieth week, it is already impossible to examine the blood for hormones.
When conducting a diagnostic study, experts assess:
- The structure of the fetus and the condition of internal organs.
- The length of the cervix (the norm is 36-40 mm).
- Quality and quantity of amniotic fluid (norm - 1-1,5 liters).
- The condition of the placenta (norm - degree of maturity 0).
As for the baby, we will give an example at the time of 18 weeks:
- Weight - 160-215 g.
- The height is 20-22 cm.
- The average size of the fetal head is 3.8-5.5 cm.
- The size of the cerebellum is 1.5-1.9 cm.
- The diameter of the heart is 1.5-2 cm.
- The diameter of the humerus is 1.9-3.1 cm.
- The diameter of the femur is 1.8-3.2 cm.
- The diameter of the abdomen is 3.1-4.9 cm.
Obtained norms of ultrasound allow the doctor to draw an opinion on possible deviations in development and to resolve the issue of additional studies.
As we have already said, the timing of the second screening for pregnancy is established in accordance with WHO recommendations. Due to the triple test, experts determine the level of three markers: hCG, free estriol and alpha-fetoprotein.
A blood test is recommended during the seventeenth week of pregnancy. Screening, or rather, the received indicators, is processed by a special program. The result is known only after two weeks.
Analysis requires little preparation. Doctors advise a day before the trip to the laboratory to exclude from the diet citrus, seafood, chocolate and cocoa, as well as fatty and fried foods. Eating should be no less than 4-6 hours. It is permissible to drink 150 ml of plain water in four hours.
Let's take a closer look at the markers that appear in the triple test. The production of hCG is produced by the chorion of the fetus. Overestimated values can signal a multiple pregnancy, toxicosis or diabetes in a pregnant woman. In combination with low levels of the other two hormones, doctors presume the risk of Down syndrome.
Underestimated values of hCG allow to draw conclusions about ectopic or undeveloped pregnancy, the threat of interruption or death of the fetus, as well as chronic placental insufficiency. The risk of Edwards syndrome increases.
AFP is a plasma protein of the blood, first produced in the yolk sac, and then in the digestive tract and liver of the fetus. A low level of AFP indicates Down's disease or Edwards disease, low placenta, diabetes maternity.
An overestimated hormone level can signal a risk of brain damage, kidney anomalies, duodenal atresia, neural tube defects and anterior abdominal wall. In addition, an increase in indicators is possible in the case of Rhesus-conflict, lack of water, threats of abortion, and the death of a child.
The synthesis of the hormone occurs in the liver of the fetus and the placenta. In the normal course of pregnancy, the level of estriol is steadily increasing, which contributes to the preparation of mammary glands for lactation and improvement of blood flow in the uterine vessels. However, a sharp increase or decrease in its level can cause serious concern.
The decreased values of estriol indicate the risk of miscarriage, anemia of the child, delay in physical development or intrauterine infection. There is also the possibility of developing Down's syndrome, fetoplacental or adrenal insufficiency. Abnormal nutrition and taking antibiotics can also lead to a sharp decrease in values.
An overestimate level of estriol may be a sign of a multiple pregnancy or liver disease. In addition, specialists with a sharp reduction in the hormone predict premature birth.
About the results
So, the strictly established terms of the second screening during pregnancy and the results of the tests allow us to draw preliminary conclusions regarding the presence or absence of genetic diseases.
However, there are factors that can influence the triple test. For example, carrying out IVF, multiple pregnancies, incorrect definition of the gestation period, diabetes mellitus, as well as excess (or insufficient) weight of a woman.
It is believed that if the indicators of ultrasound and a blood test are within normal limits, then the baby is most likely healthy. The reverse situation is the basis for assuming the risks of many pathologies, but on the basis of screening, no obstetrician-gynecologist will diagnose. In this case, the attending physician recommends additionally conducting other studies (amniocentesis, expert ultrasound and cordocentesis), from which future parents have the right to refuse.
From the beginning of the 14th to the end of the 27th week, the second trimester lasts. Screening is troubling to a pregnant woman, because according to the results of the study, she may be at risk. There is no greater grief than the illness of a child, even the unborn.
Diseases, which doctors suggest by the results of the triple test:
- Down Syndrome. It appears immediately after conception, when an extra chromosome appears in the egg or sperm. Thus, in the fetus, instead of 46 chromosomes, 47 are formed (superfluous in the 21st pair). The probability of Down syndrome is 1-1.5%. Predicting the disease is impossible beforehand, but to a small extent, the age of the mother influences its appearance.
- Edwards Syndrome. It occurs similar to Down's syndrome, but the extra chromosome is in the 18th pair. The babies born in time outwardly resemble preterm: weak, painful and very small, with numerous defects in parts of the body and internal organs. Children with Edwards syndrome rarely live until their first birthday. Probability of the disease is 1 case per 5000 newborns.
- Defect of the neural tube. On the 20th day of pregnancy a neural tube is formed - first as a plate. In a few days, she should fold into the tube. This process proceeds quite unnoticed, and it is impossible to fix the problem in the early stages. The nerve tube may not completely close or turn around later, because of this the child has hernias and clefts of the spine.
The timing of the second screening for pregnancy is selected in such a way as to detect these defects.