A 36-year-old woman, gravida 3 para 2, at 35 weeks gestation comes to the emergency department due to leakage of fluid and painless vaginal bleeding. The patient had rupture of membranes 30 minutes ago; the fluid was initially clear but became bloody a few minutes later. She had normal fetal movement earlier today. The patient has not received prenatal care this pregnancy; her 2 previous pregnancies resulted in term cesarean deliveries. She has hypertension but stopped taking her medication when she became pregnant. Temperature is 36.1 C (97 F), blood pressure is 140/96 mm Hg, and pulse is 92/min. The uterus is nontender. Speculum examination confirms rupture of membranes; the cervical os is 1 cm dilated with minimal vaginal bleeding. Doppler ultrasound is unable to detect fetal heart tones. Which of the following is the most likely cause of this patient's presentation?
Vasa previa | |
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FHR = fetal heart rate; ROM = rupture of membranes. | |
Normal fetal vessels travel in the umbilical cord surrounded by thick, gelatinous tissue (ie, Wharton jelly) that protects the vessels. In contrast, vasa previa is an aberrant condition in which fetal vessels overlie the cervix surrounded only by thin fetal membranes. Their location over the cervix and lack of protection by Wharton jelly make these vessels prone to tear with rupture of membranes or contractions.
Vasa previa is typically diagnosed on fetal anatomy ultrasound at 18-20 weeks gestation, and patients normally require third-trimester, inpatient management with early cesarean delivery at 34-35 weeks gestation (ie, prior to the onset of contractions or membrane rupture). However, vasa previa may be clinically diagnosed when patients, such as this one, present with rupture of membranes accompanied by painless, minimal vaginal bleeding that primarily reflects fetal blood loss from a torn fetal vessel. Vaginal bleeding is minimal because total fetal blood volume is low (~250 mL, or 1 cup); however, hypotension from fetal bleeding leads to fetal heart rate abnormalities (eg, bradycardia, sinusoidal pattern) and rapid (eg, within minutes) fetal exsanguination and demise.
(Choice A) Patients with hypertension are at higher risk for abruptio placentae, a premature separation of the placenta from the uterus that can cause vaginal bleeding and fetal compromise. However, it also typically causes severe abdominal pain and a tender, hypertonic uterus, which are not seen in this patient.
(Choice B) Intraamniotic infection can cause fetal death, particularly in patients with prolonged (ie, >18 hr) membrane rupture. This patient has no fever or uterine tenderness, making this diagnosis unlikely.
(Choice C) Patients with prior cesarean deliveries are at increased risk for placenta previa, which can also present with painless vaginal bleeding. However, bleeding from placenta previa is primarily maternal blood loss and, therefore, usually heavy and persistent rather than minimal and transient. In addition, signs of maternal hemorrhagic shock (eg, hypotension, tachycardia) are typically present prior to severe fetal compromise.
(Choice D) Patients with prior uterine surgery are at increased risk for uterine rupture, which can present with fetal demise; however, these patients typically have associated, sudden-onset abdominal pain and uterine tenderness.
Educational objective:
Vasa previa is a rare condition in which fetal vessels overlie the cervix, making them prone to tear with rupture of membranes or the onset of labor. Patients with vasa previa may have painless, minimal vaginal bleeding and rapid fetal deterioration or demise.