The first screening or first trimester screening is a comprehensive study that identifies fetal development pathology.
Most often this is Down syndrome, Edwards syndrome and malformations of the nervous system, which can lead to disability or non-viability of the future baby.
This study consists of two stages – the blood test stage and an ultrasound examination.
The last thing may be performed as a transvaginal ultrasound examination (when the sensor is inserted into the vagina), and also, as an abdominal ultrasound examination (when the doctor examines the fetus through the abdominal).
The first trimester screening is usually performed at 11-13 weeks of pregnancy, when all organs and systems of the fetus are formed.
It should be noted that it was previously intended only for women who were in the risk group, namely:
- who already have children with genetic diseases;
- who worked in harmful or hazardous working conditions;
- who took medications that were incompatible with fetal life or threatening its health;
- who had genetic pathologies in the family;
- who had a miscarriage;
- who have not reached the age of 18 or have crossed 35 years old. As a rule, during this period either the risk of developing fetal pathologies increases, or the chances of childbearing reduce.
In the last decade, the first screening is recommended to do absolutely for everybody. This is explained, on the one hand, by the deterioration of the environment or the presence of harmful habits of future parents. On the other hand, the ability to detect pathology in a timely manner, to conduct additional diagnostics, for example, the сhorionic villus sampling (the geneticist will tell about) and begin treatment. In most cases it ends successfully.
How to prepare for the first screening?
- Within 1-3 days prior to the screening, a woman should refrain from:
- typical allergens (chocolate, citrus, seafood);
- Fried and fatty food;
- Meat (the day before the examination).
- Just before the first ultrasound screening with the transducer, which is used over the abdomanal surface, the bladder should be filled. You can do this by drinking 0,5 l of water for half an hour before the procedure. In the case of a transvaginal ultrasound method, no special preparation is required.
- The blood test should be done on an empty stomach.
What can the first screening show?
- The first screening can detect the location of the fetus in the uterus and thus exclude ectopic pregnancy;
- it can determine the number of fetus;
- it can evaluate the future baby's heartbeat, assessing the chances of its viability;
- it can control the development process of the internal organs.
During the first ultrasound screening, the specialist determines the specific indicators and checks them for compliance with the norms:
- Crown–rump length (CRL) can range from 33 to 49 mm (for a period of 10 weeks), 42 to 58 mm (11 weeks), 51 to 83 mm (12 weeks).
- Nuchal translucency (NT), which allows you to determine the presence of Down syndrome.
Ideally, it is 1.5-2.2 mm in 10 weeks, 1.6-2.4 mm in 11 weeks, 1.6 – 2.5 in 12 weeks, 1.7 – 2.7 mm in 13 weeks .
- Heart rate. Normally for 10 weeks it should be 161 – 179 beats per minute, 153 – 177 beats per minute for 11 weeks, 150 – 174 beats per minute for 12 weeks, 147 – 171 beats per minute for 13 weeks.
- Biparietal diameter (BPD) is one of the basic biometric parameters used to assess fetal head size and is 14 mm in 10 weeks, 17 mm in 11 weeks, 20 mm in 12 weeks, 26 mm in 13 weeks.
- The nasal bone, which also indicates the presence of Down syndrome and in 12 – 13 weeks it is at least 3 mm normally. It's impossible to evaluate it before.
In parallel with the evaluation of the data obtained in the first screening, a placenta examination is conducted to determine its condition, maturity, and the method of attachment to the wall of the uterus.
Biochemical blood test shows:
- Human chorionic gonadotropin (hCG) – the level ranges from 25.8 to 181.6 ng / ml in 10 weeks;
17.4 – 130.3 ng / ml in 11 weeks; 13.4 – 128.5 ng / ml in 12 weeks; 14.2 – 114.8 ng / ml in 13 weeks.
- Protein A level, or RARR-A;
- glucose level.