fetal cardiac chamber

Dear doctor,
I'm 26 years old and this is my first pregnancy.
This week I did Ultrasound (gestation age 21 weeks). While doing the scan my doctor asked me if my husband is my relative or not, I told her that he is my first cousin.. I was too much worried and I asked her why? is there any abnormality in my fetus?. She said that cardiac chamber can'not be seen cleary. She gave me an appointment after 3 weeks to repeat the scan. Is it correct that in this age (21weeks) the fetal cardiac chamber is not clear to set any diagnosis?

[Marie M Gleason, M.D.]

By 21 weeks of gestation, the fetal heart is fully developed. After that it is just a matter of growing along with the rest of the baby. It is an excellent time to visualize the fetal heart anatomy and function.  It is a common time for us to look for major heart defects.  There are times when the baby's position in the womb makes it difficult to see the heart clearly, and it is common to ask women to return for re-imaging at another time.  However, if the heart chambers cannot be seen clearly at the subsequent study, then a referral to a fetal cardiologist would be indicated to rule out a congenital heart abnormality. If there is consanguinity (you and your husband are closely related genetically) then it does raise the chances of congenital anomalies of all types in the baby.