Introduction
Michael A. Schellpfeffer, M.D.
Two cases of vasa previa ended with neonatal survival as a
result of aggressive intrapartum management. The etiology and
pathophysiology of vasa previa are reviewed. The current
status of prospective diagnosis is presented, as are the
essentials of successful neonatal management of this condition.
(j Reprod Med 1995;40:327-332)
Keywords: placenta, labor complications.
From Kenosha, Wisconsin.
Presented at the 52nd Annual Meeting of the Wisconsin Society
of Obstetrics and Gynecology, Middleton, July 1992.
Address reprint requests to: Michael A. Schellpfeffer, M.D., 1400 75th
Street, Kenosha, WI 53143.
0024-7758/95/4004-0327/$1.50/0 (9) The journal of Reprodu Journal of
Reproductive Medicine
Despite continued advances in diagnostic and therapeutic
modalities in obstetrics, there still remain several clinical
entities that strike fear in the hearts of all who practice
obstetrics. One such entity is vasa previa. Due to its rare
occurrence and subtle presenting signs and symptoms,
vasa previa remains a clinical problem usually diagnosed
retrospectively and usually results in a poor perinatal
outcome. Indeed, in the > 200 years in which this
condition has been described, the fetal mortality has not
been changed appreciably.
The clinical entity of vasa previa occurs in an estimated
1 in 2,761-5,000 pregnancies. By definition, vasa previa
occurs when fetal vessels traverse the internal os of the
uterine cervix without the structural support of the
placenta or umbilical cord. This is associated only with
placentation involving a velamentous insertion of the
umbilical cord or a bilobed or succenturate-lobed
placenta with membranous vascular connections (Figures
I and 2). In multifetal pregnancies, especially greater than
twins, the incidence of velamentous insertion of the
umbilical cord increases.
The fetal mortality rate associated with vasa previa
varies from 50% to 90% in collected series.12 Previous
authors have stratified the fetal risk into several
categories depending on the maternal symptoms and
signs at the time of diagnosis: (1) asymptomatic, (2)
vaginal bleeding, (3) vaginal bleeding with fetal heart
rate abnormalities, and (4) status of the amniotic
membranes. The reports, then, vary with increasing
maternal symptomatology, reflecting increasing risk to
the fetus.
The following cases illustrate two instances of vasa
previa in which immediate, aggressive neonatal
management was undertaken. This resulted in a favorable
outcome even in the face of the poor prognostic signs of
vaginal bleeding and fetal heart rate abnormalities.
Case Reports
Case 1
A 20-year-old, Hispanic woman, para 1011, at 36 weeks'
gestation was admitted to the labor-and- delivery suite in
early active labor. An unusually heavy "bloody show' was
noted with progression of the patient's labor. A
consultation was obtained by the patient's family
practitioner concerning the unusual bloody show and a
question about fetal heart rate decelerations. Pelvic
examination revealed the patient's cervix to be 8 cm
dilated, with
bulging fetal membranes in front of a vertex presentation.
Fetal heart rate decelerations were noted on external fetal
heart tone monitoring. An amniotomy was accomplished,
with placement of an internal fetal scalp electrode.
Immediately the fetal heart rate dropped to 30-40 beats
per minute (Figure 3), with bloody amniotic fluid from
the vagina. The patient was instructed to push and
progressed to complete cervical dilation almost
immediately. She was transferred to a delivery room, and
forceps were applied to the fetal head, at +3 station with
an occiput posterior position, to expedite delivery. With
delivery of the fetal head, a veil of fetal membrane with
vessels was noted covering the occiput, and the diagnosis
of vasa previa was made.
The male infant weighed 2,700 g. Apgar scores were 1,
3 and 4. The infant was extremely pale and hypotonic,
with clinical evidence of hypovolemic shock. Mask
ventilation and subsequent intubation were accomplished
immediately, and he was stabilized. An umbilical venous
catheter was then placed immediately, and a transfusion
was under- taken with un-cross-matched 0(-) blood. A
total of 27 mL of packed red blood cells and 20 mL of
lactated Ringer's solution was administered initially. The
infant responded dramatically to this treatment, with
marked improvement in color and vital signs.
Subsequently, the attending pediatrician arrived and
further stabilized the infant for transfer to a tertiary care
neonatal intensive care unit (NICU). Initial laboratory
studies obtained from an umbilical artery catheter
revealed a hemoglobin and hematocrit of 17.2 g/dL and
52.7%, respectively.
The infant's NICU course was remarkable for transient
evidence of acute tubular necrosis, hyper-
administered subcutaneously to decrease the patient's
contraction frequency. The fetal heart rate tracing
improved transiently, but recurrent fetal heart rate
decelerations necessitated emergency preparations for an
abdominal delivery.
A primary low transverse cesarean section was
performed, and a female infant was born weighing 3,400
g, with Apgar scores of 2 and 4. Upon delivery, the infant
was extremely pale and hypotonic. Clinically the diagnosis
of hypovolemic shock was established. Immediate
neonatal resuscitation was begun with mask ventilation
and subsequent intubation and positive pressure
ventilation. A large amount of blood was aspirated from
the respirato- ry passages as well as the stomach of the
infant. Frothy, pink secretions were also noted from the infant's respiratory tree after intubation.
In view of the obvious evidence of hypovolemic shock,
the author broke scrub from the cesarean section and
immediately placed an umbilical venous catheter. The
infant was transfused with 10 mL of heparinized cord
blood, 15 mL of un-cross-matched 0(-) packed red blood
cells and 30 mL of normal saline. Almost immediately the
in- fant's clinical status improved. The matemal surgery
was completed, and the infant was transerred to the
newborn nursery. Evaluation and care by the attending
pediatrician and consulting neonatologist ensued. The
initial hemoglobin and hemat-
bilirubinemia and the need for two subsequent
transfusions prior to transfer back to the delivering
hospital. Neurologically the infant demonstrated
irritability for the first three days of life; it resolved
spontaneously prior to transfer. Decreased head control
and tone were also noted but also resolved spontaneously
prior to discharge from the delivering hospital.
Follow-up by the child's pediatrician over seven years
demonstrated normal growth and development, with no
evidence of abnormal sequelae.
The mother's postpartum course was completely
uneventful. A pathologic examination of the placenta
confirmed the diagnosis of a velamentous insertion of the
umbilical cord with rupture of membranous vascular
connections.
Case 2
A 20-year-old, white woman, para 0000, at 39 weeks'
gestation was admitted in early labor. Her labor
progressed to 3-4 cm of cervical dilation, at which time
an amniotomy was accomplished. Prior to the
amniotomy, nursing assessments of the patients' cervical
dilation had questioned the presence of 'something at the
level of the fetal membranes." External fetal heart tone
monitoring prior to amniotomy was reported as normal.
Approximately one hour after amniotomy an episode of
progressively worsening variable/late decelerations was
noted, with an associated increase in bloody show. A
consultation was obtained by the patient's family
practitioner after placement of an internal fetal scalp
electrode, which confirmed the fetal heart rate
decelerations (Figure 4). Terbutaline, 0.25 mg, was
ocrit were 16.2 g/dL and 46.0%, respectively. An initial
chest roentgenogram revealed bilateral, diffuse pulmonary
infiltrates consistent with aspiration pneumonia. The infant
was stabilized with two additional transfusions of 0(-)
packed red blood ceus because of persistent hypotension
and evidence of hypoperfusion. Transfer was then
accomplished to an NICU.
The NICU course was relatively uneventful. Initially the
infant was given an additional 35 mL of 5% human plasma
protein and treated prophylacticauy with intravenous
antibiotics and anticonvul- sants. The pneumonia resolved
without sequelae. There was evidence of hematuria, with
an initially elevated serum creafinine level, but this, too,
quick- ly resolved. At no time was there evidence of neurologic abnormalities. The infant was discharged on the
10th day of life with a hematocrit of 50%. Subse- quently,
pediatric follow-up of the chidd over 1.5 years revealed
normal growth and development, with no evidence of
abnormal sequelae.
The mother's postoperative course was uneventful, and
she was discharged from the hospital on postoperative day
3. The placenta was examined grossly after the delivery
and was noted to be bi- lobed. There were membranous
vascular connec- tions between the two lobes. This was
also the site of the amniotomy. These findings were
confirmed on a formal pathologic examination.
I
The Journal of Reproductive Medicine
Discussion
In considering the nature of vasa previa, several points of
anatomy and physiology must be addressed.
Anatomically, two distinct types of abnormal
placentation give rise to a true vasa previa. First is a
velamentous insertion of the umbilical cord that traverses
the internal cervical os. Second is a bilobed or
succenturate-lobed placenta with membranous vascular
connections that traverses the internal cervical os (with
the umbilical cord inserting in the placenta proper).
The etiology of a velamentous insertion of the
umbilical cord was first proposed by von Franque in
1900. He postulated that the fetal abdominal pedicle
extended from the decidua capsularis rather than the
decidua basaus during embryogenesis and initial
placentation. This was thought to occur because of a shift
in decidual vascularization, and thus an initial richly
vascularized segment of decidua intended to become
placenta actually be- came membrane. An alternative
theory, popularized by Bernirschke and Driscoll was
advanced by Strassmann in 1902. This was the concept
of trophotropism, which held that the umbilical cord is
originally normally inserted, but due to unidirectional
lateral growth of the chorion frondosum, a velamentous
insertion ensues.
The pathophysiology of vasa previa is unique in that it
presents a life-threatening risk to the fetus but essentially
no risk to the mother. The fetus has a narrow margin of
reserve to deal with acute hypo-
volemia. According to previous neonatal data,6 a
newborn infant can experience a 15% loss of its total
blood volume without evidence of adverse cardiovascular
changes. However, with a 20-25% blood loss, shock
ensues. This is due to the relatively limited fetal/neonatal
cardiac contractility and the relatively small
fetal/neonatal blood volume. A term neonate's blood
volume is estimated at 85-100 mL /kg. This equals a total
blood volume of 250-3,50 mL in the average term infant.
Therefore, a fetus could lose a significant amount of its
total blood volume, and clinically this might be attributed
only to a heavy bloody show or possible marginal sinus
abruptio placentae. The fetal heart monitor changes that
occur often initially reflect fetal tachycardia with rupture
of the fetal vessels as the fetus at- tempts to maintain its
cardiac output. Fetal heart rate decelerations in this
condition, however, indicate an advanced state of fetal
hypovolemia and shock.
Diagnostically one needs to maintain a high index of
suspicion in at-risk cases, such as multiple gestations.
During labor a timely evaluation of abnormal vaginal
bleeding is also imperative. With the advent of more
sophisticated ultrasound technology, the possibility of an
antenatal diagnosis becomes closer to reality.
Specifically, with the ability to identify the umbilical
cord insertion into the placenta and/or scanning of the
internal cervical os with a color flow Doppler probe, this
problem can be revealed.
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Volume 40, Number 4/April 1995
Historically, the most common means of diagnosis is
palpation of fetal vessels at the level of the fetal
membranes. Amnioscopy is also a means to the
diagnosis or confirmation of it. With the onset of
abnormal vaginal bleeding, tests for fetal hemoglobin are
possible as a diagnostic modality prior to the onset of
fetal heart rate tracing abnormalities. These tests include
the Apt and the Kleinhauer-Betke. They will
qualitatively or semiquantitatively identify fetal red
blood cells by virtue of the resistance of fetal
hemoglobin to denaturing in alkaline conditions. Several
immunologic tests have also been developed to more
sensitively identify fetal red blood cells by
antigen/antibody reactions. Finally, on more of a
historical note, is the examination of smears of vaginal
blood for the presence of fetal hematologic forms.
Therapeutically, with a true prospective antenatal
diagnosis of vasa previa, an elective cesarean section
should be performed (at term or with appropriate
definitive documentation of fetal maturity) to optimize
the fetal outcome. This, in reality, is a rare situation.
More likely, to effect a favorable outcome in this
condition, an emergency cesarean section is performed
with the onset of symptoms and/or a definitive
intrapartum diagnosis. Only with a fully dilated cervix
and adequate descent of the fetal head should an
operative vaginal delivery be considered unless the fetus
is nonviable. Vacuum extraction as a method of
operative vaginal de- livery is also relatively
contraindicated unless the device can be placed on the
fetal vertex without further damage to the placental
membranous vasculature.
The cornerstone of optimizing the neonatal out- come
is rapid and aggressive neonatal resuscitative
techniques-specifically, the use of immediate basic life
support measures and establishment of vascular access
for fluid and blood component therapy. In a hypotensive,
hypovolemic neonate the latter usually involves
placement of an umbilical venous catheter. Placement of
an umbilical artery catheter is generally impossible due to
time constraints and the intense umbilical artery
vasoconstriction.
Circulatory resuscitative therapy should begin with
crystalloid and/or colloid therapy. They are generally
routinely available on an emergency basis. However, the
mainstay of therapy consists of replacement of red blood
cells as quickly as possible. This might include the use of
heparinized cord blood, but usually blood loss as a result
of the con-
331
dition precludes its use in any significant amount. More
likely is the use of un-cross-matched 0(-)
(cytomegalovirus[ - 1, if possible) packed red blood cells.
Another possible alternative is the use of heparinized
maternal blood if an 0(-) status can be assessed with
certainty from the prenatal record and if the clinical
condition of the mother warrants it.
The actual amounts of fluid and blood component
therapy will depend upon the clinical situation at the time.
The following are some general transfusion guidelines.
The generally recognized neonatal blood volume is
approximately 85-100 mL/kg. If a neonate is assumed to
have lost at least 25-50% of its blood volume to produce
clinically significant hypovolemic shock, a starting point
would be to replace roughly 50% of the blood volume with
equal volumes of fluid and blood component (10-20
mL/kg of packed red blood cells). In both cases above this
was accomplished, but during both infants' neonatal
course, further transfusions were required. The need for
further transfusions may have been the result of an
underestimation of the blood loss, with subsequent
equilibration of the neonatal circulation or iatrogenic blood
loss from multiple phlebotomies. In previous reports in
which neonatal hemoglobin and hematocrit were
documented, the initial neonatal hemoglobin and
hematocrit did not reflect the severity of the neonatal
blood loss. Clinical status, then, is the best determinant of
the acute need for fluid and blood component replacement
therapy. One must be aware of overzealous fluid and blood
component therapy, especially with improvements in the
clinical status of the infant.
In conclusion, these two cases demonstrated that with
prompt, aggressive neonatal management, even in the
face of poor prognostic signs and a retrospective
diagnosis, a favorable neonatal outcome can be
achieved. However, if the umbilical cord insertion is not
seen to arise from the placenta on an ultrasound
examination (especially in multiple gestations), a
careful search for the origin of the umbilical cord must
be undertaken, including the use of color flow Doppler
scanning, to rule out vasa previa.