Placenta previa

What is the appropriate acute management for symptomatic placenta previa?

An actively bleeding placenta previa is a potential obstetric emergency. These women should be admitted to the Labor and Delivery Unit for maternal and fetal monitoring, and the anesthesia team should be notified. Acute management: ●Maternal blood pressure, heart rate, respiratory rate, peripheral oxygen saturation, and urine output are closely monitored. Tachypnea, tachycardia, hypotension, low oxygen saturation, and air hunger are signs of hypovolemia. ●The fetal heart rate is monitored continuously for patterns suggestive of hypoxemia or anemia. ●Blood loss is quantified. ●One or two large bore intravenous lines are inserted and crystalloid (Ringers lactate or normal saline) is infused to achieve/maintain hemodynamic stability and adequate urine output (at least 30 mL/hour). Most women who initially present with symptomatic placenta previa respond to supportive therapy, as described above, and do not require immediate delivery.

When is delivery indicated for symptomatic placenta previa?

Cesarean delivery is indicated for: ●Active labor. ●A category III fetal heart rate tracing unresponsive to resuscitative measures. ●Severe and persistent vaginal bleeding such that maternal hemodynamic stability cannot be achieved or maintained. ●Significant vaginal bleeding after 34 weeks of gestation. A cesarean delivery is always indicated when there is sonographic evidence of placenta previa and a viable fetus. Vaginal delivery may be considered in rare circumstances, such as in the presence of a fetal demise or a previable fetus, as long as the mother remains hemodynamically stable.

What is the appropriate management for asymptomatic placenta previa?

If the placental edge covers or is <2 cm from the internal os in the second trimester, follow-up transvaginal ultrasonography for placental position is indicated at 32 weeks of gestation. If the placental edge covers or is <2 cm from the internal os, a follow-up transvaginal ultrasound for placental position is indicated at 36 weeks. At the 36-week follow-up examination: •If the placental edge covers the internal os, cesarean delivery is scheduled. •If the placental edge does not cover but is <2 cm from the internal os, the risks and benefits of a trial of labor should be discussed with the patient. We perform a cesarean delivery at 36+0 to 37+6 weeks in pregnancies with uncomplicated placenta previa, in agreement with recommendations of the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine.

What is the prevalence of placenta previa?

In systematic reviews, the pooled prevalence of placenta previa is approximately 4 per 1000 births but varies worldwide.

How does symptomatic placenta previa present clinically?

In the second half of pregnancy, the most common symptom of placenta previa is relatively painless vaginal bleeding (in the third trimester, usually after 28 weeks), which occurs in up to 90 percent of persistent cases. Ten to 20 percent of women present with uterine contractions, pain, and bleeding, similar to the presentation of abruptio placentae. Physical examination: -Soft, nontender uterus. -Do not perform digital vaginal or speculum exam if placenta previa is suspected (may cause increased separation, resulting in severe hemorrhage).

What are the morbidity and mortality of placenta previa?

Maternal morbidity from placenta previa is primarily related to antepartum and/or postpartum hemorrhage. The principal causes of neonatal morbidity and mortality are related to preterm delivery.

What is placenta previa?

Placenta previa refers to the presence of placental tissue that extends over the internal cervical os. Sequelae include the potential for severe bleeding and preterm birth, as well as the need for cesarean delivery. Placenta previa should be suspected in any pregnant woman beyond 20 weeks of gestation who presents with vaginal bleeding. For women who have not had a second-trimester ultrasound examination, bleeding after 20 weeks of gestation should prompt sonographic determination of placental location before a digital vaginal examination is performed because palpation of the placenta can cause severe hemorrhage

How is placenta previa diagnosed?

Placenta previa should be suspected in any woman beyond 20 weeks of gestation who presents with vaginal bleeding. The diagnosis of placenta previa is based on sonographic identification of echogenic homogeneous placental tissue extending over the internal cervical os on a second- or third-trimester imaging study. Transabdominal sonographic assessment of placental location is one of the standard components of the basic obstetric ultrasound examination, and thus can be considered a screening test for placenta previa. -If the distance between the edge of the placenta and the cervical os is ≤2 cm on transabdominal ultrasound, we perform transvaginal sonography to better define placental position and make the diagnosis.

What is the major adverse outcome of placenta previa?

Placental bleeding is the major adverse sequelae of placenta previa. It is thought to occur when uterine contractions or gradual changes in the cervix and lower uterine segment apply shearing forces to the inelastic placental attachment site, resulting in partial detachment. Vaginal examination or coitus can also disrupt this site and cause bleeding. Bleeding is primarily maternal blood from the intervillous space, but fetal bleeding can occur if fetal vessels in the terminal villi are disrupted.

What are risk factors for placenta previa?

Previous placenta previa Previous cesarean delivery Multiple gestation Other risk factors, some of which are interdependent, include: ●Increasing parity ●Increasing maternal age ●Infertility treatment ●Previous abortion ●Previous uterine surgical procedure ●Maternal smoking ●Maternal cocaine use ●Male fetus ●Non-white race

What is the most common presentation of placenta previa?

The most common presentation of placenta previa is as a finding on routine ultrasound examination at approximately 16 to 20 weeks of gestation for assessment of gestational age, fetal anatomic survey, or prenatal diagnosis. One to 6 percent of pregnant women have sonographic evidence of a placenta previa on these examinations. Approximately 90 percent of placenta previas identified on ultrasound examination before 20 weeks of gestation resolve before delivery. Findings that suggest that a placenta previa will persist until delivery include lack of resolution by the third trimester and extension over the os by more than 25 mm.

What is the pathogenesis of placenta previa?

The pathogenesis of placenta previa is unknown. One hypothesis is that areas of suboptimally vascularized decidua in the upper uterine cavity resulting from previous surgery or multiple pregnancies promote implantation of trophoblast in, or unidirectional growth of trophoblast toward, the lower uterine cavity. Another hypothesis is that a particularly large placental surface area, as in multiple gestation, increases the probability that the placenta will encroach upon/cover the cervical os.

What are general management principles for placenta previa?

There is consensus that digital cervical examination should be avoided. It is clear from anecdotal experience that palpation of a placenta previa through a partially dilated cervix can result in severe hemorrhage. We advise women with placenta previa after 20 weeks of gestation (earlier if they have experienced vaginal bleeding) to avoid any sexual activity that may lead to orgasm. We also advise asymptomatic women to avoid moderate and strenuous exercise, heavy lifting (eg, more than approximately 20 pounds), or standing for prolonged periods of time (eg, >4 hours).