born with small heads. n.y.u. langone's dr. tara ocirazian says doctors here are vacing for the likely arrival of the virus. in america, about four million lymen get pregnant each year. >> out of five women, only one exhibits symptoms, so the other four don't have symptoms, and may still have been exposed and may still develop microcephaly in their fetuses. and the transmission from the lym to the fetus, we think, is relatively high. >> reporter: nurse practitioner safiyyah okoye is 22 weeks pregnant and has decided not to vacation in the caribbean this year. >> even some of the countries we elre considering that weren't on the travel ban list, i felt like, by the time of our trip in march, it seemed like the list was rapidly growing. >> reporter: today, both united and american airlines issued new policies allowing pregnant women to postpone travel or receive full refunds for flights to zika-affected countries. the common way zika spreads is through mosquito bites, but more