SBA — Single Best Answer · Review
Question 17
Feto-maternal medicine → Perinatology
Classification
Question
SSBAQuestion Header
Prenatal diagnosis
Question Stem
A pregnant woman at 12+2 weeks of gestation has received a high-risk screening result for a chromosomal abnormality. Following counselling, she wishes to have a definitive prenatal diagnostic test as soon as possible. Which is the most appropriate investigation?
Options
A
Amniocentesis at 12+2 weeks
B
Amniocentesis at 14+0 weeks
C
Chorionic villus sampling at 12+2 weeks
D
Defer invasive testing until 15+0 weeks
E
Repeat screening instead of offering diagnostic testing
Explanation
Chorionic villus sampling (CVS) is an appropriate definitive prenatal diagnostic procedure at 12+2 weeks. RCOG states that CVS should not be performed before 10+0 weeks and, where possible, should be performed from 11+0 weeks onwards because procedures at earlier gestations may be technically more challenging. Amniocentesis should not be performed before 15+0 weeks because early amniocentesis is associated with an increased risk of pregnancy loss and fetal talipes. Therefore, for a woman at 12+2 weeks who wishes to proceed with definitive invasive prenatal diagnosis without unnecessary delay, CVS is the appropriate procedure.
Option Validity
A) Amniocentesis should not be performed before 15+0 weeks.
B) Amniocentesis at 14+0 weeks is still earlier than the recommended minimum gestation.
D) Waiting until 15+0 weeks is unnecessary when CVS is an appropriate diagnostic option at this gestation.
E) Further screening does not provide the definitive diagnostic information requested by the woman.
Further Reading
Navaratnam K, Alfirevic Z; Royal College of Obstetricians and Gynaecologists. Amniocentesis and chorionic villus sampling: Green-top Guideline No. 8. BJOG. 2022;129:e1-e15. doi:10.1111/1471-0528.16821.