The follow-up protocol for patients in the first trimester screening is as follows:
Based on the results of the Down syndrome screening test in the first trimester, patients are divided into seven groups:
1- Screen positive group (high risk): If the pregnant woman’s risk is greater than 1:50 (that is, the denominator of the declared risk is smaller than 50), she should be referred directly for diagnostic tests.
2- Group with intermediate risk (Borderline risk): If the pregnant woman’s risk is between 1:50 and 1:1500, it is recommended to wait until the second trimester and perform the sequential test.
3- Negative screen group (low risk): If the screening result of the first trimester is less than the discriminating risk (1:1500), the Down syndrome screening will end and the patient will only be examined for neural tube disorders or NTDs in order to measure alpha-fetoprotein and AFP MoM calculation is referred to the laboratory in the 15th to 16th week of pregnancy.
4- If the only abnormal finding in the fetus is the presence of NT above 3 mm and the mother’s age is above 35 years, she should be referred for amniocentesis.
5- If the only abnormal finding in the fetus is NT above 4 mm and the mother’s age is less than 35 years, she should be referred for amniocentesis.
6- Women of any age should be referred for echocardiography at 18-20 weeks of pregnancy if their fetus has NT above 3.5 mm.
7- According to the recommendation of the latest guide of British Colombia Prenatal Genetic Screening Program = BCPGSP of Canada, in addition to the second group, the following groups should also perform complete sequential tests:
– Women over 35 years old during childbirth (in the previous edition of the guide, the age of this group of women over 36 years old was mentioned.)
– Women with twin pregnancy
– Women who have a history of a child or fetus with Down syndrome, Edward or neural tube disorders (or parents who are carriers of any type of translocation, deletion, insertion or inversion that increases the risk of having a child with unbalanced chromosomal development ).
– Women over 35 years of age who have had 3 or more miscarriages in the past. (In the new edition of this guide, this group is removed and placed in the same first group).
– Women who are HIV positive (since performing amniocentesis in this group of women causes a possible increase in the transmission of HIV from mother to fetus, so it is better to use sequential test to reduce false positive cases of screening tests in this group of women).
– Women who have done IVF or ICSI.
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