The members of the American Academy of Pediatrics Committee on Fetus and Newborn thank Mr Whittall and the Nuffield Council on Bioethics for their correspondence and for calling attention to the recent Nuffield report, “Critical Care Decisions in Fetal and Neonatal Medicine: Ethical Issues.”1 As Mr Whittall pointed out, the Nuffield report provides a practical framework to guide decisions based on gestational age for infants born before 25 weeks’ gestation. The American Academy of Pediatrics Neonatal Resuscitation Program (NRP) Steering Committee took a similar approach in its 2005 NRP guidelines.2 They cited the infant born before 23 weeks’ gestation as an example of the category of infants for whom resuscitation would not be indicated, and they cited the infant of ≥25 weeks’ gestation as an example of one for whom resuscitation is nearly always indicated. For infants of 23 and 24 weeks’ gestation, those with uncertain prognosis, they indicated that parental wishes should take precedence.The Committee on Fetus and Newborn considered such an approach (ie, defining the gestational age below which resuscitation should not be undertaken and another gestational age above which resuscitation should be routine), with decisions in the intermediate range guided primarily by the wishes of informed parents. However, we decided against this categorical approach for several reasons. First, the prognosis for extremely premature infants is influenced by other factors besides gestational age, such as fetal gender and corticosteroid exposure. Second, we avoided proposing gestational-age guidelines because we felt that these demarcation lines are not fixed but have moved over time and may continue to do so. Third, the concept of standard gestational-age cutoffs for active intervention is problematic because there is considerable center-to-center variability in outcome below 25 weeks’ gestation, both in mortality3–6 and morbidity7; ideally, decisions should be based on prognosis. However, much of the variability in outcome among centers results from differences in the attitudes and beliefs of medical staff regarding the potential for intact survival at very early gestation.8–12 In fact, it is not possible to isolate the impact of the attitudes of medical providers on prognosis from other factors that contribute to center-to-center variability in outcome in the United States and other medically advanced countries.The worldwide variation in potential outcome at the threshold of viability dwarfs the magnitude of center-to-center variability in the United States and United Kingdom. The guidelines of the Nuffield Council on Bioethics and the NRP Steering Committee may be reasonable for the United States and the United Kingdom in 2007, but these specific gestational-age boundaries would not be appropriate in many parts of the world where maternal-fetal medicine and neonatal intensive care are not as advanced.13To be truly useful, an approach using default gestational-age cutoffs to guide therapy would have to allow for consideration of other factors in addition to completed weeks of gestation. As an example, a female fetus at 24 weeks, 6 days, whose mother received betamethasone has a better prognosis than a male fetus at 24 weeks, 0 days, whose mother did not receive corticosteroid. In addition, the guidelines would need to be reappraised every few years as new outcome information becomes available.The Nuffield report is a thorough and scholarly document. Insofar as treatment decisions at the threshold of viability are sometimes made primarily on the basis of gestational age, the guidelines proposed in the Nuffield report are valid in medically advanced countries in the early 21st century. We commend the Nuffield Council on Bioethics for their efforts in producing this important document, and we welcome the discussion it has stimulated.