Final answer:
The recommended initial first trimester screening test for fetal aneuploidy is a combination of maternal blood tests and ultrasound measurements. These tests assess the risk of the fetus having certain chromosomal abnormalities.
Step-by-step explanation:
The recommended initial first trimester screening test for fetal aneuploidy is a combination of maternal blood tests and ultrasound measurements. This screening is commonly referred to as the first trimester combined test or integrated test. It involves a blood test to measure the levels of specific hormones, such as pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG), as well as an ultrasound measurement of the nuchal translucency (NT) – the thickness of the fluid-filled space on the back of the baby's neck.
The results of these tests, combined with the mother's age and sometimes additional factors, can provide an assessment of the risk of the fetus having certain chromosomal abnormalities, including Down syndrome (trisomy 21) and trisomy 18.
It's important to note that the first trimester screening is a screening test and not a definitive diagnostic test. If the results indicate a high risk of aneuploidy, further diagnostic tests, such as chorionic villus sampling (CVS) or amniocentesis, may be recommended to confirm the diagnosis.