If you suffer from certain genetic illnesses, or carry a gene for that illness, scientists can take one or two cells to check for those genes and transfer only healthy embryos.
Scientist cannot tell healthy embryos from unhealthy embryos.
( z1 possible :polarity - :ARG1 ( z2 tell :ARG0 ( z3 scientist ) :ARG1 ( z4 embryo :mod ( z5 healthy ) ) :ARG2 ( z6 embryo :mod ( z7 healthy :polarity - ) ) ) )