Fetal cells recovered during amniocentesis are grown in tissue culture. what mitotic phase are the chromosomes recovered from these cells arrested at for karyotype examination?

Karyotype examination needs to be done at metaphase.

In karyotype test, the examiner is trying to find whether the chromosome is having any abnormality.  In metaphase, the chromosome is easier to count and observed.
A chemical (colchicine) will be given to make the cells stuck at metaphase.