I have a question about a second trimester ultrasound (23 weeks) that showed small long bones in one of my fraternal twin fetuses (the male fetus). Measurements were FL is 34.8mm, HL is 32.7mm. All other aspects of the ultrasound were normal- brain, heart, kidney, and bowels looked good/normal. First trimester ultrasound (12 weeks) showed nuchal translucency at 1.10 and 1.50, and the nasal bone was present/visible in both fetuses. Blood work for first trimester scan was- free beta hCG 42.90 IU/I, .751 MoM; PAPP-A .850 IU/I, .197 MoM. The ultrasound doc said the blood work pointed to a small increase in the risk for trisomy 18 (not 21), but added that with twins, blood work is not reliable/predictive.

During the second trimester US, the doc said the short long bone lengths raised the Downs risk for the male fetus from appox 1/2,700 to 1/28. That was less than welcome news. My wife is 30 years old patientold. We have decided against amnio, as we plan to keep both babies regardless.

Can you put the above into perspective (more than statistical risk) for me? Do you consider short humerus and femur one marker, or two?