The onset of labor is a complex neuroendocrine event involving the release of the hormone oxytocin from the baby's pituitary gland into the maternal circulation. This hormone stimulates uterine contraction. Labor is divided into three stages. The first stage begins at the onset of regular contractions, which cause progressive dilation of the cervix. The latent phase of this stage is from the start of labor to approximately 4 cm (1.6 in) dilation, and the active phase is from the end of the latent phase to approximately 10 cm (3.9 in), which is complete dilation. At the end of this stage, the baby's head begins to move down the birth canal, accompanied by a bloody discharge from the vagina and a marked change in contractions. This is known as the transition stage and marks the end of the first stage and the beginning of the second stage of labor. It may last from a few minutes up to several hours.
The second stage of labor begins at the onset of complete dilation and continues to the birth of the baby. The fetal membranes can rupture during these first stages of labor or prior to the onset of contractions. Generally, labor follows shortly after spontaneous rupture of membranes. The third stage of labor begins at the birth of the baby and continues through the expulsion of the placenta. In general, the contractions of the uterus get progressively stronger and closer together over the course of labor.
MODERN BIRTH PRACTICES
Over the years there has been an increased emphasis on childbirth as a natural process to be shared by the father and sometimes the extended family. This has given rise to alternatives in the location and the way in which birth has been handled. Approximately 90 percent of all births in the United States occur in hospitals, but many hospitals have built on-site birthing centers with a homelike atmosphere.
Birth can take place outside the hospital, depending on a woman's risk for complication and the training and expertise of the care providers. Freestanding birthing centers and home birth for very low-risk women account for most of the remaining births.
Fear of anticipated pain of childbirth creates body and muscle tensions that in turn make the labor process more difficult and unnecessarily painful. It is very common for women to attend some type of childbirth-preparation class during the latter weeks of pregnancy. The three most common techniques of so-called natural childbirth are the Lamaze Method, or psychoprophylaxis technique; the Leboyer Technique, or gentle birth technique; and the Bradley Method, or "husband coached" technique. Use of any of these methods can enhance the family's birth experience and lead to a decrease in the amount of analgesia and anesthesia needed for birth. Many women find these techniques all that is necessary for pain management.
When pain of labor is too intense for the mother, or when an operative birth is required, drugs can be given for relief. Narcotics and sedatives are used intravenously or intramuscularly to reduce anxiety and give some pain relief at certain times in labor. Regional anesthesia, in the form of local and epidural blocks, is becoming increasingly popular. General anesthesia includes various combinations of barbiturates, narcotics, and muscle relaxants.