Welcome to HCM.
Initially you had twin gestation out which one aborted very early in the pregnancy
where as the other survived with fetal anomalies, which could be detected only later on in the pregnancy and as a precaution the obstetrician waited for some more time, before advising termination of pregnancy.
Most likely both the fetuses had congenital anomalies in which one of the fetuses was not at all compatible with life so aborted in the initial stages itself wheres as the other fetus continued for some more time. These are most likely to be genetic disorders, though many other anoomalies could lead to fetal ascites
. The drugs duphaston
and maintain are routinely used by numerous obstetricians throughout India and these abnormalites due to the drugs have not been reported.
I think the centre where the fetus was sent for genetic study could be MediScan,of Dr. Suresh.
Wish you best of every thing.