Multiple Gestation (2005)
Implications of Chorionicity
Ultrasonography of Nuchal Cords
David M. Sherer, MD
Professor of Obstetrics and Gynecology
State University of New York (SUNY),
Downstate Medical Center
Brooklyn, NY
Multiple Gestations (2005)
Implications of Chorionicity
Twin Gestation
• Marked recent increase in the incidence of
twinning and other high-order multiple
gestations reflects impact of ART
• Current incidence 1:40 deliveries
• Approximately 50% of twin gestations
currently result from infertility treatment.
• Increased representation of older patients
already at increased risk for adverse
perinatal outcome
Twin Gestation
• Significantly increased perinatal morbidity and
mortality rates in comparison with singleton
gestations.
• Perinatal mortality rate 3-7 fold higher than
among singletons.
• While accounting for only 2.5% of the population,
twins account for 12.6% of all perinatal morbidity.
Twin Gestation
• Monozygotic twinning constant across populations
– 1 in 250 births
– independent of maternal age and parity
• Dizygotic twinning rates vary between
– 1 in 20 and 1 in 500 births
– rates vary with maternal age, parity, genetic factors and
ART
• It is estimated that 20% of all twins are
monochorionic and 80% are dichorionic
• Monozygotic and monochorionic twins are
associated with a relatively high incidence of
perinatal morbidity and mortality
Increased Morbidity & Mortality
•
•
•
•
Preterm birth
Fetal growth restriction
Low birthweight
Congenital anomalies
Increased Morbidity & Mortality
• Problems unique to twin gestations
– Twin Twin Transfusion, Twin Reverse Arterial
Perfusion, Conjoined Twins, Cord Entanglement
• Twofold increase in spontaneous abortion
• Birth trauma
• Overall increase in maternal complications
(preeclampsia, pregnancy-induced hypertension,
gestational diabetes, placental abruption, placenta
previa, both ante and postpartum hemorrhage)
Twin Gestation
Morbidity and Mortality
• Perinatal mortality rate for monozygotic
twins is approximately 3 fold higher than
for dizygotic twins
Twin Gestation
Morbidity and Mortality
• Mortality in monochorionic twin gestations
is almost twice as high as dichorionic twin
gestations (and fourfold higher than
singletons)
(Machin G, et al Am J Med Genet 1995;55:71-6)
“Hidden Mortality” of
Monochorionic Twin Gestations
• Data from nuchal translucency screening of 102
monochorionic and 365 dichorionic twins
– Higher rate of fetal loss prior to 24 weeks gestation
(12.2% vs.1.8%)
– Perinatal mortality < 32 wks (2.8% vs. 1.6%)
– Prevalence of preterm delivery (9.2% vs. 5.5%)
– Prevalence of birthweight < 5th centile in both twins
(7.5% vs. 1.7%)
– While overall, MC twins sustained a 3 fold increase in
loss of both twins in comparison with DC twins, the
proportion of birthweight discordancy > 25% was
similar (11.3% vs.12.1)
(Sebire et al. BJOG 1997;104:1203-7)
TVS depiction of chorionic and
amniotic type at < 14 wks
• 212 multifetal gestations scanned < 14 wks
• Number of fetuses and chorionic and amniotic
were determined ultrasonographically
• Of 212, 54 delivered in the authors institution, and
of these 43 had pathology assessment of the
placenta (40 twins and 3 sets of triplets)
• All US membrane assessments were precise
• Conclusion: TVS US < 14 wks accurately depict
chorion and amnion type in multifetal pregnancies
(Monteagudo A et al AJOG 1994;170:824-9)
Chorionicity and Perinatal Outcome
• Perinatal morbidity and mortality differ among
twin gestations of varying membrane and
placental arrangements
• Compared with dichorionic twins, monchorionic
twins exhibit a 3-5 fold higher incidence of
perinatal morbidity and mortality
(Bajora R, Kingdom J. Prenat Diagn 1997;17:1207)
Chorionicity and Perinatal Outcome
• Prospectively assessed outcomes of 68 twin
gestations diagnosed in the first-trimester with two
active fetal hearts as a function of chorionicity,
• The outcome of dichorionic twin gestations was
significantly better than monochorionic twins
(83% vs. 56% delivered twins, 12% vs. 11%
delivered singletons and 5% vs. 33% none,
respectively)
• Interestingly among dichorionic twins, pregnancy
outcome was less favorable when diagnosed
between 6 -8 weeks vs. 8-13 weeks
(Benson C. Ultrasound Obstet Gynecol 1993;3:343-5)
Chorionicity and PerinatalOutcome
• Retrospective cohort study of 44 MC and 164 DC
twin gestations followed > 20 weeks assessed the
effect of chorionicity on infant outcome at 1 year
of age
• Adverse outcomes (death, cerebral palsy and
mental retardation) occurred in 10% (9/88) of MC
vs. 3.7% (12/328) DC infants.
• Delivery did occur on average 1 week earlier
(34.7±2.8 vs 35.7 ±2.3) in MC vs. DC twins
(Minakami et al. J Reprod Med 1999;44:595-600)
Chorionicity & PerinatalOutcome
• However, no significant difference in GA at birth
or birthweight were noted between 9 MC and 12
DC infants with adverse outcomes
• TTT was considered etiology of adverse outcome
in 7 MC infants
• All nine MC and 33% (4/12) DC infants with
adverse outcomes belonged to twin pairs that had
birthweight discordancies
≥ 25%
(Minakami et al. J Reprod Med 1999;44:595-600)
Fetal Death of One Twin
• Antepartum death of a single fetus
complicates between 2.5% and 5% of all
twin gestations and is associated with
significant morbidity and mortality in the
survivor
Fetal Death of One Twin
• Intrauterine fetal demise of one of the twins is 3-4
times more common in monochorionic twins, yet
by no means unique to MC gestations
• Carlson and Towers reported 17 cases of a fetal
death among 642 multiple gestations
• No major morbidity or mortality occurred among
survivors of dichorionic twins
(Carlson and Towers, Obstet Gynecol 1989;73:685-9)
Fetal Death of One Twin
• Compared outcomes between 50 MC vs. 42 DC
twin gestations with one fetal demise
• Among MC twins, the incidence of fetal demise of
the co-twin (13/50 vs. 1/42) and total perinatal
mortality rate (29/50 vs. 9/42) were higher in the
MC group
• Among MC group anemia was noted in 19/37 of
the surviving co-twins
(Bajora et al. Hum Reprod 1999;14:2124-300)
Twin Gestation
• Fetal testing of twins includes
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–
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Fetal movement assessment
Nonstress testing
Biophysical profile
Doppler velocimetry
US (interval fetal growth)
• The above surveillance methods have not
been assessed prospectively (randomized or
sratified according to chorionicity)
Twin Gestation
• Assessed 37 patients with twins who received care
prior to 32 weeks with25 patients with no care/or
presented >32 weeks
• Statistically significant differences were noted in
the perinatal mortality rate of monitored (68/1000)
vs. non-monitored patients (160/1000).
• Significant differences were observed in mean
birthweights (2645 g vs. 2007 g, respectively)
(Gardner et al, J Reprod Med 1990;35:519-21)
Twin Gestation
Randomized 8662 women to receive (or not receive)
routine US screening
• All twins were detected in the US group vs. 76.3%
of controls.
• Perinatal mortality was 27.8/1000 vs. 65.8/1000
among controls
(Helsinki Ultrasound Trial, Saari Kempainen et al,
Lancet 1990;336:387-91)
Summary
• A marked lack of objective evidence-based
data are available as to the precise preferred
surveillance modalities and recommended
intervals between testing of twins in
general, irrespective of chorionicity.
Summary
• It appears reasonable to maintain that
– The DC twin gestation represents a high-risk
pregnancy
– The MC-DA twin gestation represents a very
high-risk pregnancy
– The MC-MA twin gestation represents an
extremely high-risk pregnancy
Summary
• Early prenatal knowledge of chorionicity is
important
• Nevertheless, at least until definitive (prospective
randomized) data become available, DC twin
gestations should not be exempted from increased
fetal surveillance applied to twins
• Twins should be followed routinely with interval
US growth assessments (3-4 week intervals)
• Targeted surveillance of MC twins may be
implemented at critical (early) gestational ages
Prenatal Ultrasonographic
Diagnosis of Nuchal Cords
Pathogenesis of Nuchal Cords
• Unclear.
• It appears that fetal movements may result in the formation
of nuchal cords.
• Excessive fetal movement and long umbilical cords - are
prone to entanglement.
• Does not explain why some fetuses develop nuchal cords
and others do not.
Incidence of Nuchal Cords
• Frequency of nuchal cords increases with
advancing gestational age (from 5.8% to 29.0%
between 20 and 42 weeks’ gestation, respectively).
• Ranges between 15.8% and 30%.
• Single, double, triple, quadruple loops; at 10.6%,
2.5%, 0.5% and 0.1%, respectively (Br J 1957).
• Single, double, triple loops; at 21.7%, 1.7%, and
0.3% (J Fam Prac 1992).
• Nuchal cords may reduce spontaneously.
Perinatal Outcome (1)
• Unclear whether or not nuchal cords are
associated with increased adverse perinatal
outcome.
• Associated with neonatal shock and anemia.
• Increased incidence of intrapartum “fetal distress”.
Perinatal Outcome (2)
• Fetuses with nuchal cords were associated with a
significantly increased prevalence of variable decelerations
of the FHR versus matched controls in both the first and
second stages of labor.
• Umbilical artery pH, 7.25 vs. 7.27 (P<.05).
• Umbilical artery acidemia usually mixed (68%) or
respiratory in origin (23%).
• Metabolic acidemia was infrequent (9%).
(Hankins GV et al, Obstet Gynecol 1987;70:687-91).
Perinatal Outcome (3)
• Retrospective, case control study of 167 infants with
nuchal cords vs. 523 controls.
• Fetal bradycardia and variable decelerations occurred
significant more often in the nuchal cord group (18.6% vs.
9.6%).
• No significant differences in operative deliveries or 1, 5
minute Apgar scores.
• Neonates with nuchal cords weighed significantly less than
controls.
(Miser et al, J Fam Prac 1992;34:441-4)
Perinatal Outcome (4)
Compared with single or no cord entanglement,
pregnancies with multiple nuchal cords were more
likely to have
– Meconium-stained amniotic fluid
– Intrapartum fetal heart rate changes
– Operative vaginal delivery
– Low 1 minute Apgar scores
– Mild umbilical artery acidosis at birth
(Larson et al, Am J Obstet Gynecol 1995;173:1228-31)
Perinatal Outcome (5)
• Among 70 women delivering infants with nuchal cords,
there were significantly increased incidences of
– Meconium-stained amniotic fluid
– Severe intrapartum variable decelerations
– Fetal bradycardia
• These authors suggested that in the presence of
oligohydramnios, nuchal cord might represent an increased
risk of intrapartum FHR changes.
(Strong et al, J Reprod Med 1992;37:718-20)
Perinatal Outcome (6)
• Although it is extremely difficult to prove
causality, nuchal cord(s) have been
implemented in occurrences of intrauterine
fetal death.
Previous Diagnostic Modalities
• Spontaneous testing:
– Increased incidence of variable FHR decelerations (≥3
episodes, ≥15 bpm, lasting 15 sec).
– “Double” or “W” pattern of FHR.
• Evoked testing:
– Recording FHR following manual transabdominal
compression of fetal neck (82.3% sensitivity and
89.1% specificity).
– FHR decelerations following vibroacoustic stimulation.
Ultrasonography of the
Umbilical Cord
• Traditionally not performed uniformly due to:
– Objective difficulty (2D depiction of “free
floating” narrow structure in 3D environment).
– Fetal movement
– Lack of immediate availability of color Doppler
imaging
– Lack of institutional guidelines.
– Dependent on “determination” of sonographer.
Ultrasonography of the
umbilical cord
• The umbilical cord exhibits coiling (helical twists),
• Fetuses with non-coiled umbilical cords are at increased
risk for adverse perinatal outcome.
• Nuchal cords, have less vascular coiling.
• Potentially, the coiled umbilical cord may be able to
withstand vascular stretching and compression associated
with nuchal entanglement.
Ultrasonography of nuchal cords
• Requires a high-degree of suspicion (due to the
sonolucent nature of umbilical vessels).
• Represents a “fixed point” of the umbilical cord,
specifically in the vicinity of the fetal neck.
• Become significantly easier with high-resolution
ultrasound with the “divot” sign representing circular
indentations of the fetal nuchal skin (Ranzini et al, Obstet
Gynecol 1999;93:854).
• Care should be excercised not to confuse posterior cystic
masses, folds of skin or amniotic fluid pockets, with the
“divot” sign.
Ultrasonography of Nuchal Cords
• The condition renders itself to color Doppler imaging.
• Both sagittal and axial sections (cross-section and linear,
respectively) are required to avoid overdiagnosis.
• Doppler flow velocimetry may be applied to confirm
diagnosis.
• 3D ultrasound may improve prenatal diagnosis.
Color Doppler Ultrasound of
Nuchal Cord
• Color Doppler imaging correctly identifies 72% of single,
and 94% of multiple nuchal cords found at birth.
• Overall sensitivity of color Doppler ultrasound in the
prenatal detection of nuchal cords is 79%.
• Greater sensitivity noted after, rather than before 36 weeks’
gestation (93% vs. 67%), possibly reflecting spontaneous
reduction with earlier diagnosis.
(Jauniaux et al, Ultrasound Obstet Gynecol 1992;2:417-9)
Color Doppler Ultrasound of
Nuchal Cord
• Reported sensitivity and specificity of intrapartum color
Doppler ultrasound diagnosis of nuchal cord, 96% and
97%, respectively.
(Funk et al, Geburtshilfe Frauenheilkd 1995;55:623-7)
(Qin et al, Ultrasound Obstet Gynecol 2000;15:413-7)
• 3D surface imaging does not provide more useful
information than conventional 2D or color Doppler
ultrasound in detecting nuchal cords.
(Hanaoka et al, Ultrasound Obstet Gynecol 2002;19:471-4)
Single Nuchal Cord
(sagittal view)
Single Nuchal Cord
(color Doppler, sagittal view)
Single Nuchal Cord
(color Doppler, axial view)
Single Nuchal Cord
(color Doppler, axial view)
Single Nuchal Cord
(color Doppler, axial view)
Double Nuchal Cord
(sagittal view)
Double Nuchal Cord
(color Doppler, sagittal view)
Double Nuchal Cord
(color Doppler, axial view)
Double Nuchal Cord
(color Doppler, axial view)
Doppler Flow Velocimetry of
Nuchal Cord
• Abnormal Doppler flow waveforms suggesting an
obstruction to flow have been reported in
association with true knots of the cord.
• Potential waveform abnormalities include:
– systolic notching of the umbilical artery waveform.
– poststenotic acceleration of umbilical vein flow.
– absent end diastolic flow (reported with nuchal cord).
Doppler Velocimetry of
Nuchal Cord
Doppler Velocimetry of
Nuchal Cord
Doppler Velocimetry of
Nuchal Cord
3D Ultrasound
Single Nuchal Cord
3D Ultrasound
Double Nuchal Cord
3D Ultrasound
Triple Nuchal Cord
Ultrasonography of Nuchal Cords
• Disregard?
“don’t ask, don’t tell”
• Inform?
• Monitor?
• Intervene?
Suggested Modified Management
• Information regarding the presence of nuchal
cord(s) should not be withheld.
• Findings should be discussed openly in real-time
with the patient, preferably by a Perinatologist.
• Should be explicitly stated on the written report
generated following US examination.
Patient Counseling,
Should Address
• Reassurance as to the highprobability of unaffected outcome.
• Critical importance of fetal
movement assessment.
In addressing Clinical Management
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•
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Number of involved nuchal loops.
Amniotic fluid volume status (AFI).
Gestational age.
Fetal growth.
Fetal Testing Indicated
• Significantly decreased amniotic fluid
volume.
• Postdates.
• Fetal growth restriction.
• Decreased fetal movements.
Fetal Testing Should Include
•
•
•
•
Nonstress test.
Biophysical profile.
Doppler flow velocimetry
Potentially, evoked tests including:
– Vibroacoustic stimulation
– Oxytocin challenge test
With less than optimal fetal testing
• Delivery should be considered
Potentially, application of these
new guidelines, may decrease the
occurrence of third-trimester
in-utero fetal demise associated
with nuchal cords.
In summary:
Ultrasonographic depiction of a
nuchal cord should be
• Recorded in the patient’s chart.
• Fowarded to the patient and her physician.
• Managed with close fetal surveillance
including fetal movement counts and
interval fetal testing.
• In selected cases, may indicate delivery.