Hi! Both of my twin boys had a pic line. (They were 10 weeks premature weighing 3lbs. and 2lbs. 15oz.) They can go in different spots. My boys had theirs in their arms, but they are sometimes in the leg, foot or even head. The head one sounds bad, but it is just under the skin and the babies don't even know they are there. They actually tried to put one in Andrew's head, but it didn't take. There are risks, as with anything, but the benefit outweighs any risk in my opinion. The main risk is infection. However, a pic line is used in place of an IV. Due to the smallness of preemie veins, it is hard to keep an IV in for more than a couple of days. So, they use a pic line when an IV is needed for an extended period. This goes from the vein to the artery and can stay in for weeks. This way they don't have to constantly change the IV, which results in a lot of pokes for the baby!
I'm assuming that you have a little one in the NICU, so they should have tons of information you can read about pic lines and other preemie info. Speak to your neonatologist or your NICU nurse. They were always really helpful to me. Good luck!! My guys were in the NICU for 6 weeks so let me know if I can help any other way!