During the antenatal period you should have had an opportunity to discuss feeding your baby with your midwife so that you could make an informed choice.
Breastfeeding gives your baby all the nutrients he/she needs for the first six months of life, and continues to benefit them along with solid foods for many months. It can help protect him/her from infection and other diseases and help reduce the chances of getting some illnesses later in life.
https://www.unicef.org.uk/babyfriendly/wp-content/uploads/sites/2/2010/11/otbs_leaflet.pdf
https://www.sciencedaily.com/releases/2016/07/160729092524.htm
If your baby is initially unable to be breastfed for clinical reasons you may need to start expressing as soon as possible after the birth so that the baby they can either have your breastmilk via a nasogastric tube/bottle, or so that your milk can be stored ready for when feeds can be initiated.
The link below to the Best Beginnings website will take you step by step through expressing breast milk for a premature or sick baby to initiating breastfeeding. It will also give you hints and tips on how to encourage your milk supply. https://www.bestbeginnings.org.uk/small-wonders
Multiple births can make breastfeeding a little more challenging, but the following leaflet will give you excellent hint and tips on how to breastfeed twins, triplets or more. If you are formula feeding this can also be a little more challenging but the useful tips will help you through.
http://www.multiplebirths.org.uk/MBFParentsFeedingGuideFINALVERSION.pdf
For some premature and sick babies Human Donor Breastmilk might be the best option if you are struggling to produce enough breastmilk in the early days. The following link gives you information on donor breastmilk http://www.ukamb.org/
If you had initially decided to formula feed you might consider breastfeeding or expressing in the short term for your preterm/sick baby due to the additional health benefits to be gained from breastmilk.
If you have chosen to use formula milk for your baby staff will advise you whether a standard formula milk can be used or if your baby requires a specialised formula due to their weight or condition. If this is the case then ask to speak with the paediatric dietician who will be able to discuss the best formula milk for your baby.
You’ll also need to know how to prepare formula milk once home and how to sterilise equipment, the following link can help with this http://www.nhs.uk/Conditions/pregnancy-and-baby/pages/bottle-feeding-advice.aspx
The above link is also useful for women expressing and giving breastmilk via a bottle.
However you choose to feed your baby remember skin-to-skin contact and spending time with your baby will help you feel closer to them.