An anaesthetist places an epidural in the lower back, in the space just outside the membrane around the spinal cord (the epidural space). Numbing medicine (local anaesthetic) is then given through a thin tube (catheter) that stays taped in place. It blocks pain signals travelling from the uterus and birth canal to the brain. That is why it relieves labour pain without putting you to sleep. It is the most effective labour pain relief available and is considered safe when given with routine monitoring.
What it feels like, and why the baby is largely unaffected
The sensation is heaviness and warmth spreading down from the waist rather than complete numbness. You feel contractions as pressure instead of pain. As pushing gets closer, the dose is usually lowered so you can still feel when to push. The medicine goes into the epidural space, not a vein. So very little enters your bloodstream, and very little crosses the placenta. Unlike opioid pain-relief injections, an epidural does not make the baby drowsy. The one indirect way it can affect the baby is a temporary drop in the mother's blood pressure. That is why your blood pressure and the baby's heart rate are both monitored after it is started. An epidural is not the same as a spinal, which is a single injection into the spinal fluid and is typically used for a planned caesarean. What an epidural actually feels like, and is it safe for the baby? covers the practical details in full.