I can appreciate your concerns as this is the second time you are having Down Syndrome and syphilis scare. The
bacteria which cause syphilis, Treponema pallidum, are normally present in the mouth and oral swabs are often
showing false positive results in pregnancy. In your case, this could be the reason for false positives. So,
specific antibody tests are done to rule out syphilis.
AFP levels alone are not indicative of Down Syndrome. You will need other tests (blood estrogen and HCG
levels) and ultrasound to confirm or refute the suspicion. In Downs syndrome, AFP and estrogen are low and HCG
is very high. Amniocentesis is done in highly suspicious cases.
If you have placenta previa, then you may need regular ultrasounds to manage the progress of the baby. So, the
radiologist will also closely monitor for signs of Downs Syndrome. Also, as pregnancy approached full term,
placenta is often pulled up and the placenta previa disappears.
Please feel free to ask anything else you may want to know. Take care!