Have heard of this a few times.  With one mother, she continued to have
problems during breastfeeding, and responded to nifedipine (long
acting), 30 mg daily.  I have had an obstetrician phone me about this as
well, but I did not hear from the mother after she delivered.  It
doesn't seem rare, but probably not common either.  Nifedipine can
apparently also be used during pregnancy.

Jack Newman, MD, FRCPC