International Technologist in Cytogenetics ASCP Practice Test

In pregnancies at increased risk for trisomy 18, serum analytes display specific patterns that differ from those seen in normal pregnancies or those at increased risk for other conditions like trisomy 21.

In the case of trisomy 18, the commonly observed pattern is characterized by low levels of alpha-fetoprotein (AFP), low levels of human chorionic gonadotropin (hCG), and low levels of unconjugated estriol (uE3). This is due to the chromosomal abnormalities affecting fetal development and hormone production.

Low AFP is often indicative of neural tube defects, but in the context of trisomy 18, it aligns with the decreased production of various substances by the abnormal placenta and fetus. Similarly, low hCG and low uE3 levels also reflect the altered endocrine environment associated with the trisomy 18 condition, as both peak in normal pregnancies during specific gestational periods, while in trisomy 18 cases, these peaks are not achieved due to the genetic disorder.

Understanding these biomarkers is crucial in prenatal screening processes, as identifying such patterns can aid healthcare professionals and parents in assessing the risks for chromosomal abnormalities in the fetus.