Final answer:
Trisomy 21, or Down Syndrome, is the most likely karyotype abnormality in the stillborn fetus with the described abnormalities, due to characteristic symptoms that align with those of Trisomy 21. The correct option is A. Trisomy 21
Step-by-step explanation:
The most likely karyotype abnormality in a stillborn fetus delivered at the 28th week of gestation, with features such as flat facial features, excessive skin at the posterior neck, a ventricular septal defect, and duodenal atresia is likely Trisomy 21, also known as Down Syndrome. This condition is characterized by an extra chromosome 21, leading to developmental and physical abnormalities. A karyotype analysis revealing the presence of three chromosome 21 copies confirms the diagnosis of Trisomy 21.
The gestational period described in the question, along with the noted abnormalities, aligns with known symptoms and characteristics of Trisomy 21. These include cardiac defects such as ventricular septal defects and gastrointestinal issues such as duodenal atresia, in addition to distinctive facial and physical features. The fetal development described, including the facial structure formation and body proportion, changes during weeks 21-30, provides context to the timeline at which the stillborn fetus was delivered. The correct option is A. Trisomy 21