In Louise Gosbell's article,"'As long as it's healthy': What can we learn from early Christianity's resistance to infanticide and exposure?"she notes that "the New Testament is silent on the issues of infanticide and exposure."
However, David Instone-Brewer has argued that a prohibition against infanticide can be found in Acts 15 (“Infanticide and the Apostolic Decree of Acts 15,” Journal of the Evangelical Theological Society 52 : 301-321). I argued last November at the annual Evangelical Theological Society that Instone-Brewer's argument is not ultimately persuasive so I think Gosbell is correct.
Gosbell's article is worth a read in any case.