See below link from Rav Silberstein of Bnei Brak (SIL of Rav Elyashiv ZTL) for detail regarding nowadays that there is an incubator etc. See what he quotes from the Rogatchover and the psak of the Chazon Ish that ‘nishtaneh heteva’.
http://www.hebrewbooks.org/pdfpager.aspx?req=28410&st=&pgnum=83