176 Obstetrics and Gynecology Board Review •••
❍ What is the most common adnexal mass visualized during a first trimester ultrasound?
The corpus luteum.
❍ The resistance index (RI) and pulsatility index (PI) of the uterine artery decline from 6 to 12 weeks’
gestation due to?
Establishment of the intervillous circulation.
❍ Name some fetal anomalies that can be detected with reliability in the first trimester.
Large encephalocele, holoprosencephaly, ectopia cardis, and conjoined twins.
❍ Name a few major malformations that should NOT be diagnosed in the first trimester.
Renal agenesis, anencephaly, Dandy-Walker malformation, hydrocephalus, and omphalocele.
❍ Nuchal translucency (NT) is performed between which gestational weeks?
10 to 14 weeks.
❍ What variables are used to calculate the Down syndrome risk when performing NT?
The NT measurement, the CRL, the gestational age, and the age of the mother.
❍ What value for NT is generally considered abnormal?
3 mm or greater.
❍ What percentage of fetuses with an abnormal NT will have aneuploidy?
About 75%.
❍ Which congenital abnormality is associated with an abnormal NT, but normal karyotype?
Congenital heart disease (in 27%).
❍ Fetuses with abnormal NT and normal karyotype and anatomy may be at increased risk of what?
Preterm delivery and growth restriction.
❍ What are the advantages of first trimester aneuploidy screening?
The potential for earlier diagnosis, which can be confirmed by CVS, allowing for earlier, less traumatic termination
with more privacy.
❍ What is the difference between NT and nuchal skin fold (NSF) measurements?
NT is a first trimester measurement, while NSF is a second trimester measurement.
❍ How does the NT change with gestational age?
It increases from 10 to 14 weeks’ gestation.