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Essentials of Diagnosis

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  • Labor is a sequence of uterine contractions that results in effacement and dilatation of the cervix and voluntary bearing-down efforts, leading to the expulsion per vagina of the products of conception.
  • Delivery is the mode of expulsion of the fetus and placenta.

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Pathogenesis

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Labor and delivery is a normal physiologic process that most women experience without complications. The goal of the management of this process is to foster a safe birth for mothers and their newborns. Additionally, the staff should attempt to make the patient and her support person(s) feel welcome, comfortable, and informed throughout the labor and delivery process. Physical contact between the newborn and the parents in the delivery room should be encouraged. Every effort should be made to foster family interaction and to support the desire of the family to be together. The role of the obstetrician/midwife and the labor and delivery staff is to anticipate and manage complications that may occur that could harm the mother or the fetus. When a decision is made to intervene, it must be considered carefully, because each intervention carries both potential benefits and potential risks. The best management in the majority of cases may be close observation and, when necessary, cautious intervention.

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Physiologic Preparation for Labor

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Before the onset of true labor, several preparatory physiologic changes commonly occur. The settling of the fetal head into the brim of the pelvis, known as lightening, usually occurs 2 or more weeks before labor in first pregnancies. In women who have had a previous delivery, lightening often does not occur until early labor. Clinically, the mother may notice a flattening of the upper abdomen and increased pressure in the pelvis. This descent of the fetus is often accompanied by a decrease in discomfort associated with crowding of the abdominal organs under the diaphragm (eg, heartburn, shortness of breath) and an increase in pelvic discomfort and frequency of urination.

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During the last 4–8 weeks of pregnancy, irregular, generally painless uterine contractions occur with slowly increasing frequency. These contractions, known as Braxton Hicks contractions, may occur more frequently, sometimes every 10–20 minutes, and with greater intensity during the last weeks of pregnancy. When these contractions occur early in the third trimester, they must be distinguished from true preterm labor. Later, they are a common cause of “false labor,” which is distinguished by the lack of cervical change in response to the contractions.

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During the course of several days to several weeks before the onset of true labor, the cervix begins to soften, efface, and dilate. In many cases, when labor starts, the cervix is already dilated 1–3 cm in diameter. This is usually more pronounced in the multiparous patient, the cervix being relatively more firm and closed in nulliparous women. With cervical effacement, the mucus plug within the cervical canal may be released. ...

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