This patient's clinical presentation is consistent with placenta previa. Transabdominal ultrasounds have a false-negative rate of up to 7% for this condition, so high-risk patients should be further evaluated with a transvaginal ultrasound.
Placenta previa is characterized by placental implantation over some or all of the internal os. It is most common in older, multiparous women, as well as women with a history of previous placenta previa. Classic symptoms include painless bleeding during the third trimester, either during rest, or after activity or coitus. Diagnosis is made by ultrasound, with transvaginal ultrasound being more sensitive than transabdominal ultrasound. If the fetus is less than 37 weeks and the mother is hemodynamically stable, expectant management can be used to allow the fetus to mature inside the womb. However, emergent Caesarian section is required at any fetal age if the mother is at risk of severe blood loss, or if fetal heart rate is compromised.
Sakornbut et al. review bleeding in late-trimester pregnancy. They note that placenta previa is often diagnosed in patients earlier than 20 weeks gestation, but the condition will resolve by 28 weeks in 90% of such patients. Therefore, placenta previa in early pregnancy should be reevaluated at 28 weeks by ultrasound.
Raisanen et al. performed a case control study to determine whether placenta previa is a risk factor for birth of a child that is small for gestational age (SGA). They found that placenta previa was not associated with SGA neonates in nulliparous women. However, there was a significant association between SGA neonates and placenta previa in multiparous women.
Illustration A shows the three major types of placenta previa. Illustration B shows the three major types of placenta accreta, one of the most important complications of placenta previa.
Answer 1: IV magnesium can be used as a tocolytic in patients with placenta previa who present in labor before 37 weeks gestation, but this patient is not in labor.
Answer 2: Emergency Caesarian section should be performed in patients with maternal life-threatening bleeding or concerning fetal heart rate changes.
Answer 3: Patients with suspected placenta previa should not undergo bimanual or speculum exams, as these procedures increase the risk of bleeding.
Answer 5: This patient has a high risk for placenta previa, and further diagnostic testing should be pursued.
Sakornbut E, Leeman L, Fontaine P. Late pregnancy bleeding. Am Fam Physician. 2007 Apr 15;75(8):1199-206.
PMID:17477103 (Link to Abstract)
Räisänen S, Kancherla V, Kramer MR, Gissler M, Heinonen S. Placenta Previa and the Risk of Delivering a Small-for-Gestational-Age Newborn. Obstet Gynecol. 2014 Aug;124(2 Pt 1):285-91.
PMID:25004348 (Link to Abstract)