What is the recommended initial screening test for fetal aneuploidy in the first trimester?

The recommended initial screening test for fetal aneuploidy in the first trimester is a combination of pregnancy-associated plasma protein A (PPA), beta-hCG, and ultrasound to measure nuchal translucency. This approach is advantageous because it allows for an early assessment of the risk for conditions such as Down syndrome (Trisomy 21) and Trisomy 18 by combining biochemical markers and imaging.

The measurement of nuchal translucency, which assesses the fluid accumulation at the back of the fetus's neck, paired with the concentrations of PPA and beta-hCG in maternal serum, helps to create a risk profile for aneuploidy. When combined with the appropriate gestational age, this screening provides a non-invasive method that is effective for early detection and can guide decision-making for further testing or maternal-fetal medicine consultation if risk factors are present.

In contrast, options like amniocentesis, used for definitive diagnosis, are not suitable for initial screening because they are invasive and carry risks of miscarriage. Maternal serum alpha-fetoprotein, beta-hCG, estriol, and inhibin-A are typically part of the second-trimester screening (the quad screen) rather than the initial assessment in