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 GestationMorbidity and Mortality

• Perinatal mortality rate for monozygotic twins is approximately 3 fold higher than for dizygotic twins

Twin GestationMorbidity 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– 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 ofNuchal Cord

Doppler Velocimetry ofNuchal Cord

3D UltrasoundSingle Nuchal Cord

3D Ultrasound Double Nuchal Cord

3D UltrasoundTriple 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 high-probability of unaffected outcome.

• Critical importance of fetal movement assessment.

In addressing Clinical Management

• 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.