First Trimester Screening

Combined first trimester serum screening includes an ultrasound for measurement of nuchal translucency (fluid area behind the neck) and serum measurement of two proteins in the blood called free beta and PAPP-A.  The ultrasound can be done between 10 weeks 0 days and 13 weeks 6 days following the first day of your last menstrual period.  The levels of free beta and PAPP-A are combined with the nuchal translucency measurement to provide a new risk assessment for Down syndrome and trisomy 18.  In addition, 40% of babies with congenital heart defect have a thickened nuchal translucency. 

Studies have shown that the detection rate of Down syndrome is between 80-90% and the detection for trisomy 18 and 13 is greater.  This test does not detect all babies with chromosomal abnormalities.  If the first trimester screen is positive, tests including CVS (chorionic villus sampling) or amniocentesis are the recommended follow-up evaluations.   

The CVS procedure involves taking a biopsy of the placenta.  There is approximately a 1% risk of miscarriage as a result of CVS.  There is a small chance that additional testing would need to be done in the case of ambiguous results.  An association between CVS done before 10 weeks and limb reduction defects has been reported.  The timing of CVS is therefore after 10 weeks of pregnancy. 

The amniocentesis procedure involves obtaining some of the amniotic fluid surrounding the baby.  This procedure is usually done starting at 15 weeks.  There is a less than 0.5% chance of miscarriage with this procedure.  The accuracy of the chromosome analysis is estimated at greater than 99.4%.  Results take, on average, 10-14 days. 

The benefits of prenatal testing include reassurance, or in the event of a problem, preparation, optimal medical management or termination. 

Those who have first trimester screening, will still need a second trimester AFP (alpha fetal protein) to screen for spina bifida. 

YOU SHOULD FIRST CHECK WITH YOUR INSURANCE COMPANY TO SEE IF THE FIRST TRIMESTER SCREENING IS INCLUDED IN YOUR COVERAGE.