An epidural is a regional anesthetic that can be given at any stage of labor to numb the abdomen and therefore block the pain of contractions, but it's typically given when the woman is at least 4 cm dilated. In some cases, if a woman's labor progresses very quickly and she doesn't request one right away, she may not be able to get one before delivery. Epidurals are the most popular form of pain relief during labor in the US, with more than half of pregnant women delivering in hospitals choosing this treatment.
How epidurals work
A hollow needle is inserted between two vertebrae in the lower back. A tiny plastic tube is then passed through the needle and into the epidural space surrounding the spinal cord. A local anesthetic is injected into the needle and flows through the tube into the epidural space so that the nerve roots carrying the pain stimulus to the brain are coated with anesthetic and pain is reduced or completely blocked. This will affect sensation in your legs so that you need to remain in bed and your baby will be closely monitored. A stronger epidural also affects sensation in your bladder, so you will need to have a catheter. Used late in labor, a stronger epidural may mean that you need help to push the baby out, since the pelvic floor muscles will be heavy and ineffective. In this case, your doctor will put a hand on your abdomen to feel when a contraction starts and will tell you when to push. In some cases, an assisted delivery becomes necessary.
When are epidurals used?
Epidurals can be used throughout labor, but they're typically given during active labor when a woman is 4-5 cm dilated. Since everyone has varying pain thresholds, the time when one is requested varies. There are factors to bear in mind should you opt for an epidural late in labor. To minimize the risks, you must remain completely still during the placement of the epidural tube. If your labor has progressed too far to enable you to do this, the anesthesiologist may refuse to proceed with an epidural for your own interest. Also, if you choose to have an epidural late in labor, it may be necessary to give a high dose so that it takes effect in time, which has disadvantages (see Considering an epidural).
If you're considering using an epidural, inform your doctor early in labor so that she can consult the anesthesiologist. The anesthesiologist may then discuss this with you and take a brief medical history to ensure that it's safe for you to have an epidural. She will discuss any risks, and answer any questions that you or your partner has, all of which can save time later on if you decide to go ahead.
There are occasions when an epidural is not advised. These include cases where a woman has had spinal surgery or is taking blood-thinning medication. Rarely, a woman may have an infection that could be exacerbated by an epidural.