First and Second Trimester Programs
Biochemical Markers
During pregnancy, there are many pregnancy related products detected in maternal blood. These products include fetal cells, fetal nucleic acids and biochemical molecules. Four of the pregnancy-associated biochemical markers constitute our First Trimester Screening (FTS) program.
By the four marker combination, 70.4% of Down's syndrome (DS) pregnancies were detected, with a 5% false positive rate (FPR)7. With the inclusion of nuchal measurement the DS detection was increased to 88.4%, whilst maintaining FPR at 5%.
Optimum Time for Testing:
Much has been made of the “one-stop shop” model for First Trimester Screening. Whilst this model may suit some practices, it does not necessarily confer optimal diagnostic performance.
For detection of Trisomy 21, maximal diagnostic efficiency for PAPP-A is achieved at 10 – 11 weeks gestation. Therefore, it is quite acceptable to perform biochemistry analysis at 10 – 11 completed weeks, and schedule the nuchal scan for 11 – 12 weeks. With our rapid (24hr) turn-around time, first trimester biochemistry MoM values are available, for incorporation into risk assessment software, well in advance of the patient’s appointment for NT scan.
Time Line and Test Options
When considering prenatal testing, your patient has many options. With respect to prenatal screening, the first trimester program is primarily focussed on feto-placental aneuploidy (and viability), whereas, at midgestation, screening is focussed on fetal structure (such as NTD). For this reason, it is recommended to consider first and second trimester programs as complementary.
From the above schematic, at the Sonic Clinical Institute we have established a seamless First and Second Trimester screening program. This has obvious advantage in those situations where patients are uncertain of dates.
Salient Features of Screening Program:
References:
