Maternal serum screening and genetic counseling

The earliest protocol for maternal serum screening to detect chromosomal abnormalities in the fetus was screening during the second trimester measuring alpha feto-protein, human chorionic gonadotrophin and estriol (detects about 69% of Down syndrome). The next generation of this screening protocol was the quad screen – which added inhibin A to the substances screened for (detects 81% of Down syndrome). The next step in the evolution of serum screening was the first trimester screening which included measuring pregnancy-associated plasma protein-A (PAPP-A) and Human chorionic gonadotropin (hCG) and measuring nuchal translucency by ultrasound. While the detection rate of second trimester screening was 81%, first trimester screening can detect 82-87% of Down syndrome. Combining the first and second trimester screening increases the detection rate to 90-95%.
What does this evolution of screening mean for the consumer/patient? To make an informed decision on whether to avail of the testing, the patient has to understand the benefits and limitations of each of them. Timing of the testing (first trimester vs second trimester) is one factor to be considered. The detection rate of the various protocols is another. The limitations of each of the protocols is yet another (second trimester screening can detect neural tube defects whereas first trimester screening cannot). The highest detection rate is obtained by combining first and second trimester screening. However the patient has to wait until results of the second trimester screening is available for calculating the risk for Down syndrome.
If a patient decides to have the screening and already in the second trimester, there is no difficulty in decision making since the choice is limited; only second trimester is possible. However if the patient is in the first trimester, deciding between first trimester and combing first and second trimester screening can be difficult, particularly if the first trimester results are abnormal. Counseling prior to participating in the screening program is vital in ensuring that the patient is informed about its sensitivity and about the meaning of false positives and false negatives. Even in developed countries, real counseling is often conducted only after a positive serum screening result is made and an invasive procedure (amniocentesis or chorionic villus sampling) is discussed as the next level of testing. In developing countries where serum screening is now being made available, are patients provided with appropriate counseling prior to the screening? When the screening results are positive for a chromosome abnormality, are there adequate facilities for follow up invasive procedures and cytogenetics studies?
As always as soon as new scientific information is available, it is applied in the clinical arena, irrespective of how complex the information is for the patient to understand or how complicated the logistics are for reaping the full benefit of the information. The article “First-trimester screening: dealing with the fall out” (Fisher J in Prenatal Diagnosis 31:46-49, 2011) discusses parental anxiety that is associated with prenatal screening procedures such as ultrasonography and the need to have facilities available to deal with this anxiety. An important facility is the the availability f trained professionals who have the skills to help patients make an informed decision as well as help deal with their anxiety.