Explain the effects analgesics and anesthesia on childbirth.

Medication is administered in over 80% of births in the United States. Analgesics, such as tranquilizers, may be used in small doses to relieve pain and to help the mother relax. These drugs pass through the placenta to the fetus and are associated with decreases in heart rate and respiration. Newborns exposed to some medications show signs of sedation and difficulty regulating their temperature. Anesthesia is a painkiller that blocks sensations. General anesthesia blocks consciousness entirely; it is no longer used because it is transmitted to the fetus and can slow labor and harm the fetus. Today the most common anesthetic is an epidural, in which a regional anesthetic drug is administered to a small space between the vertebrae of the lower spine. The woman's lower body is numbed. There are several types of epidurals, with varying numbing effects ranging from immobilizing the lower body to numbing only the pelvic region, enabling the mother to move about (a so-called "walking epidural"). Epidurals, however, are associated with a longer delivery as they weaken uterine contractions and may increase the risk of a cesarean section.