Steroids are often used in pregnancy. There's no evidence that steroids harm your baby and doctors often give them during pregnancy to help the baby's lungs to mature (usually when labour begins before 34 weeks).
If you're planning a family or find you're pregnant while you're taking steroids, don't stop taking them but discuss things with your doctor. If you're taking steroids regularly, you may be slightly more likely to develop high blood sugar (diabetes of pregnancy), so you may need to have a test called a glucose tolerance test at 26-28 weeks. This problem usually clears up when the steroids are stopped. You won't need a test if you're taking the steroids temporarily to help the baby's lungs mature.
If you've been on high doses of steroids for a long time you may be given an extra boost of steroids to help your body cope with the stress of labour, which is routine in this situation. Women taking steroids throughout pregnancy are advised to take supplements of calcium and vitamin D to help prevent osteoporosis.
Steroids are transferred in small amounts in breast milk, but it's very unlikely to affect your baby at doses less than 40 mg daily of oral prednisolone.