You’d have to ban all females. Some women don’t show much and some will overstay a visa after getting knocked up by a citizen.
Honestly, I’d be okay with that.
Why not direct Immigration to limit tourist visas to no more
than 90 days for women of child-bearing age and stipulate that
the holders of tourist visas cannot return to the US for 270
days after their visit? Next, women must submit to a pregnancy
test at the airport or port of exit. Those testing positive will
be denied access to the US for a period of 1 year. Finally,
women showing signs of obvious pregnancy will be denied access
to the US for a period of 1 year.
No exceptions.
I would add that women who overstay their visas for any reason
that results in a viable offspring born in the US will be deported.
The child is a US citizen (according to John Roberts). They
can stay. The mom cannot.