Am I sinful for having intercourse with my sick, pregnant wife, which then led to bleeding, resulting in premature birth and the death of the baby? Should I have celebrated the newborn while she was in the hospital, and can I celebrate her now?

If the intercourse that occurred between the spouses was done with their knowledge that it would harm the fetus, then both are aggressors, and they must offer the expiation for accidental killing, and their 'asabah (male relatives on the father's side) must pay blood money to the heirs. However, if the intercourse was done with the belief that it would not harm the fetus, then there is nothing upon them, because intercourse is permissible in Islamic law. As for the 'aqiqah (definition) for the newborn, it is sunnah (definition) for it to be on the seventh, fourteenth, or twenty-first day, or at any other time it becomes easy.