Choroid plexus cysts

I went for my 18 week level II u/s two days ago.  It revealed that I am having a little boy however, they found two unilateral CPC's on his brain.  They checked every other part of the baby and all looks great (according to the perinatologist) My AFP came back as 1:2700 for Trisomy 18.  My baby is also measuring big (about a week ahead) which the perinatologist also said is good since Tri 18 babies tend to be smaller.  I was offered an amnio (I am 30) but he felt in his opinion that the risk of the amnio was much greater than the risk of Tri 18.  I go for another level II in ten weeks.  My question is, can most level II u/s find other markers pretty clearly?  The babies heart, fingers, feet and measurements all look good but I am still so nervous. Thanks!

[Lisa Kessler, MS, CGC]

It can bring a great deal of anxiety when something unexpected comes up during a pregnancy.  It is very reassuring that the perinatalogist thought that the rest of the anatomy looked great on the ultrasound.  As you know, choroid plexus cysts are a common finding on level II ultrasound and can be associated with an increased risk for trismomy 18.  However, the majority of pregnancies with isolated choroid plexus cysts do not have chromosome problems such as trisomy 18.   Regarding your question about detection rate of the ultrasound, one study found that the highest detection rate (this is the ability of the ultrasound to find markers if they are present) for markers in the second trimester is at or greater than 18 weeks gestational age.   The quality of the images from the ultrasound can also impact the detection rate.  Best wishes to you.