Diagnosis and safe management of placenta previa
As repeat cesareans increase, so do placental abnormalities
IN THIS ARTICLE
2-fold risk of congenital malformations
Most investigators report a 2-fold increased risk of fetal congenital malformations in cases of placenta previa.5 These malformations include anomalies of the central nervous system, cardiovascular system, respiratory tract, and gastrointestinal tract. Therefore, a target ultrasound examination for fetal anatomy is recommended at the initial ultrasound diagnosis of placenta previa.
Risk of fetal growth restriction warrants heightened surveillance
Some controversy surrounds the incidence of fetal growth restriction in pregnancies complicated by placenta previa. Varma38 reported that fetal growth restriction occurs in 16% of women with placenta previa and is correlated with the number of antepartum bleeding episodes. Other investigators have reported normal fetal growth in women with placenta previa.39 Given this uncertainty, serial follow-up ultrasound evaluations are usually advised for fetal growth assessment.
When patient remains asymptomatic, perform amniocentesis at 36 weeks
Some women progress to the late third trimester without any vaginal bleeding. In these women, amniocentesis is recommended at approximately 36 weeks’ gestation to assess fetal lung maturity.34,40 Elective cesarean delivery can then be planned if pulmonary maturity is documented.
The benefits of elective delivery include a stable patient and an optimally prepared surgical team, as well as the avoidance of emergent surgery, which increases the risk for maternal complications. Emergent surgery also places the fetus at greater risk for anemia, compared with elective procedures(27.7% vs 2.9%, respectively).13
Vaginal bleeding requires inpatient evaluation
Any woman with placenta previa who presents with vaginal bleeding should be admitted to the labor and delivery unit for immediate evaluation of maternal and fetal status, including an estimation of gestational age.
Initial acute care and assessment necessitate34:
If hemorrhage is life-threatening, deliver immediately
During initial evaluation, if the hemorrhage is judged to be massive and life-threatening, resuscitative measures and immediate delivery are necessary to avoid serious maternal morbidity. Recommended measures include constant monitoring of maternal status, aggressive IV fluid resuscitation, transfusion of blood and blood products, assessment of fetal status, and immediate delivery without regard to the maturity of the fetus.
A woman at term or near term (with documented fetal lung maturity) who presents with mild or moderate vaginal bleeding should be delivered via cesarean section.
Conservative management may be appropriate for mild preterm bleeding
If vaginal bleeding is not threatening to the life of the mother, and the fetus is preterm, a conservative approach with aggressive expectant management is appropriate, since most first episodes of vaginal bleeding are self-limited and rarely life-threatening to mother or fetus. Expectant management allows fetal maturation in utero without jeopardizing maternal health. If maternal and fetal health remain stable, the expectant approach allows a safe delay of delivery until the fetus matures.
Hospitalization is recommended. Candidates for expectant management should be hospitalized after the initial episode of vaginal bleeding. Once maternal and fetal conditions stabilize, the woman should be transferred to the antepartum ward for hospital bed rest with bathroom privileges. For expectant management:
Delivery is warranted for life-threatening hemorrhage, fetal lung maturity, and/or the usual maternal and fetal indications.
The question of tocolysis
Third-trimester tocolytic therapy in a woman with vaginal bleeding is controversial. In placenta previa, vaginal bleeding appears to arise from disruption of the placental implantation site as the lower uterine segment develops.41,42 It is unclear whether uterine contractions play a role, as only 20% of women with placenta previa have uterine activity at the time of vaginal bleeding.13,14,42 It is difficult to determine whether these women have true preterm labor, because digital examination of the cervix to document cervical dilatation is impossible.
Does uterine activity precipitate bleeding?
Some investigators believe uterine activity is a predisposing factor for the vaginal bleeding associated with placenta previa, and would consider tocolytic therapy in a stable patient at a premature gestational age. However, further evidence of its safety is needed.
In particular, beta-mimetics should be avoided in hemorrhaging women because their vasodilatory effects can precipitate maternal hypotension. Another side effect of beta-mimetics: maternal tachycardia,43 which may mask the hypovolemic state in women with significant hemorrhage.
Magnesium sulfate has less effect on the maternal cardiovascular system and could be a better choice in symptomatic placenta previa.41 Also consider indomethacin, which appears to have fewer adverse maternal effects.
Inpatient vs outpatient management
Because 2 to 3 weeks of maternal hospitalization can pass between the initial warning hemorrhage and delivery of the fetus, outpatient care has become an option. Several retrospective studies have demonstrated the cost-effectiveness and safety of outpatient management of symptomatic placenta previa.44,45 These studies emphasized careful patient section.
