Women who are breast-feeding should be given the opportunity to continue, for whatever reason – and wherever – they are in hospital, unless they are receiving treatment that specifically contraindicates breast-feeding.
If the admission is planned, there is time to organise care appropriate to the mother’s and baby’s needs. In certain circumstances it may be possible for the baby to stay in hospital, usually depending on hospital dynamics and the reason for admission. The mother’s plan of care should include provision of a fridge/freezer space for breast milk storage and the provision of (or use of the mother’s own) breast pump. 
Expressing and freezing breast milk prior to admission is recommended, so that there is a supply for use if the mother cannot breast-feed (e.g. because of her health or treatments that are contraindicated).
If the admission is unplanned, the mother or her family should communicate that she is breast-feeding and however serious her condition, arrangements can be made for her to express milk, or have it expressed for her, in order to maintain her supply or avoid engorgement/mastitis.

From: Journal of Family Health Care Bulletin. Directory of Breast-Feeding Advice. December 2009. Published with JFHC 2009; 19(6). http://www.jfhc.co.uk/images/stories/breastfeeding.pdf