You usually can return to your normal routine right after chest MRI.
If you got medicine to help you relax during the test, your doctor will tell you when you can return to your normal routine. The medicine may make you tired, so you'll need someone to drive you home.
If contrast dye was used during the test, you may have a bruise where the dye was injected. If you're breastfeeding, the contrast dye can be passed to your baby through your breast milk. So, you'll need to bottle-feed your baby for a short time after the test.
Ask your doctor how long you need to wait before you breastfeed. You may want to prepare for the test by pumping and saving milk for 24 to 48 hours in advance.