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Which of the following BEST represents the risk of placenta accreta in patients with placenta previa who have had 3 or more previous cesarean deliveries?
Answer: (C) 60% to 70%. Read the discussion below.
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Antepartum and postpartum hemorrhage are a major source of morbidity and mortality worldwide. Certain conditions put parturients at higher risk of significant hemorrhage. Abnormal implantation of the placenta is a major cause of life-threatening hemorrhage. Placenta previa exists when the placenta covers the cervical os. The terms complete, partial, and marginal have been used in the past to describe varying degrees of placenta previa. With the improved ultrasound evaluation techniques that are now available, the more common terminology is placenta previa if any portion of the placenta overlies the cervical os. If the placenta is near the cervical os, the term low-lying placenta is used.
The incidence of placenta previa is estimated to be about 1 in 200 term pregnancies. The etiology is not fully known, but often previous uterine trauma is a factor. The placenta may implant in a uterine scar from a previous cesarean delivery, which is typically in the lower uterine segment. The more cesarean deliveries a patient has undergone, the more likely she will develop placenta previa along with placenta accreta. Placenta accreta is an abnormal adherence of the placenta to the uterine wall and varies in severity. Placenta accreta occurs when the placenta penetrates too deeply into the wall of the uterus. A more severe form, placenta increta, occurs when the placenta invades the muscular wall of the uterus. The most severe form, placenta percreta, exists when the placenta invades through the wall of the uterus into neighboring organs, such as the bladder (Figure 1). When this occurs, cesarean hysterectomy is required and may be complicated by life-threatening hemorrhage.
Figure 1. Diagram of degrees of abnormal placental infiltration. (1) Placenta accreta is adherent to the myometrium. (2) Placenta increta invades the myometrium. (3) Placenta percreta extends beyond the uterine serosa and may invade any other organ. Modified with permission, from Reitman E, Devine PC, Laifer-Narin SL, Flood P. Case scenario: perioperative management of a multigravida at 34-week gestation diagnosed with abnormal placentation. Anesthesiology. 2011;115(4):852-857. doi:10.1097/ALN.0b013e31822ea436
A study from 2006 demonstrated the relationship between the number of previous cesarean deliveries and the risk of placenta accreta in parturients with an existing placenta previa (Table 1). The risk of placenta accreta is over 60% in the presence of placenta previa for a mother who has had 3 or more previous cesarean deliveries.
Table 1. Risk for placenta accreta among 723 women with placenta previa. Information from Silver RM, Landon MB, Rouse DJ, et al; National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol. 2006;107(6):1226-1232. doi:10.1097/01.AOG.0000219750.79480.84
|
Cesarean delivery |
Occurrence of placenta accreta (%) |
|
First |
3 |
|
Second |
11 |
|
Third |
40 |
|
Fourth |
61 |
|
Fifth or more |
67 |
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