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The puerperium, or postpartum period, generally lasts 6 weeks and is the period of adjustment after delivery when the anatomic and physiologic changes of pregnancy are reversed, and the body returns to the normal, nonpregnant state. The postpartum period has been arbitrarily divided into the immediate puerperium, or the first 24 hours after parturition, when acute postanesthetic or postdelivery complications may occur; the early puerperium, which extends until the first week postpartum; and the remote puerperium, which includes the period of time required for involution of the genital organs and return of menses, usually approximately 6 weeks.
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The uterus increases markedly in size and weight during pregnancy (approximately 10 times the nonpregnant weight, reaching a crude weight of 1000 g) but involutes rapidly after delivery to the nonpregnant weight of 50–100 g. The gross anatomic and histologic characteristics of this process have been studied through autopsy, hysterectomy, and endometrial specimens. In addition, the decrease in size of the uterus and cervix has been demonstrated by magnetic resonance imaging, sonography, and computed tomography.
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Immediately after delivery, the uterus weighs approximately 1 kg, and its size approximates that of a 20-week pregnancy (at the level of the umbilicus). At the end of the first postpartum week, it normally will have decreased to the size of a 12-week gestation and is palpable at the symphysis pubis (Fig. 10–1). In case of abnormal uterine involution, infection and retained products of conception should be ruled out.
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Myometrial contractions, or afterpains, assist in involution. These contractions occur during the first 2–3 days of the puerperium and produce more discomfort in multiparas than in primiparas. Such pains are accentuated during nursing as a result of oxytocin release from the posterior pituitary. During the first 12 hours postpartum, uterine contractions are regular, strong, and coordinated (Fig. 10–2). The intensity, frequency, and regularity of contractions decrease after the first postpartum day as involutional changes proceed. Uterine involution is nearly complete by 6 weeks, at which time the organ weighs less than 100 g. The increase in the amount of connective tissue, elastin in the myometrium and blood vessels, and the increase in numbers of cells are permanent to some degree, so the uterus is slightly larger after pregnancy.
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Changes in the Placental Implantation Site
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After delivery of the placenta, there is immediate contraction of the placental site to a size less than half the diameter of the original placenta. ...