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Entangled Umbilical Cords

Monoamniotic Twins

Intertwined Umbilical Cords
Intertwined Umbilical Cords (Arrows)

Findings:

A twin pregnancy with intertwined umbilical cords is seen. Though delivered preterm, both twins survived and a monoamniotic monochorionic twin pregnancy was confirmed.

Discussion:

The incidence of monozygotic twins is approximately one in 250 pregnancies. The amnionicity and chorionicity of monozygotic twins will depend upon when division of the morula occurs. Divsion prior to 3-4 days after conception, a time at which the trophoblast (chorion) differentiates, will resuslt in two placenta . If cleavage occurs between days 4-7 a monochorionic, diamniotic pregnancy will result and after 7 days, a monoamniotic monochorionic gestation will occur. The true incidence of monoamniotic twins is unknown, but the results of published studies put the incidence between one in 1,650 and one in 93,000 live births and between one in 33 to one in 700 twin births. Only 1% to 2% of monozygotic twins are monoamniotic.

In most studies, twins are reported to have higher perinatal morbidity and mortality rates than do singleton pregnancies. This is due to preterm delivery, congenital malformations, twin-twin transfusion syndrome and intertwining of the umbilical cords, in the case of monoamniotic twins. In the past, cord entanglement has been reported in up to 70% of monoamniotic twin pregnancies, leading frequently to death of both twins by occlusion and asphyxia. Rarely, cord entanglement may lead to single fetal death. In the past ten years the survival rate for both twins in monoamniotic pregnancies has increased to as much as 50-70% in some series.

Entanglement of the umbilical cords may be the result of monoamniotic twinning or diamniotic twinning with disrpution of the dividing membrane either naturally or secondary to a procedure such as amniocentesis. As such, an early diagnosis of two separate gestational sacs does not always mean that they will persist throughout gestation, particularly if invasive procedures occur.

When twins share the same placenta, death of one twin may result in abnormalities in the remaining twin. This is felt to be due to either thromboplastic agents that cross a shared circulation or partial exsanguination of the living twin into the circulation of the dead twin resulting in hypovolemia and selected organ infarction. This occurs by virtue of the monochorionicity and shared circulations and does not require cord intertwining.

Prior to 1990 the prevailing management of monoamniotic twins was to deliver them early, in the third trimester. This management scheme was based upon an attempt to deliver the twins prior to the occurence of cord entanglement. Management schemes involved hospitalization with bed rest and continued monitoring and delivery by cesarean section. There have been several reports indicating that if monoamniotic twins survive to the mid-third trimester (30-32 weeks) fetal death rarely occurs. The likely explanation is that with increasing size of the fetuses there is less likelihood of movement around one another resulting in cord entanglement.

A recent report by Rodis et al documents their experience with 13 sets of monoamniotic twins and compares their outcomes to a combined review of the reported literature for monoamniotic twins. The average age at diagnosis was 16.3 weeks. 12 of 13 patients had antenatal fetal surveillance consisting of nonstress tests, biophysical profiles or both beginning at 24-26 weeks gestation. Non-stress tests were performed daily in 9 patients, 2-3 times / week in 3 patients and < times / week in one patient. All patients were delivered by cesarean section. Two patients died in the neonatal period, one from congenital heart disease and one from complications of asphyxia and sepsis. Thus, the overall perinatal survival rate was 92%. The average gestational age at birth was 32.9 weeks and the average birth weight was 1669 g. Umbilical cord entanglement was noted in delivery in all patients with cord knotting in 8 of 13 patients. Two patients had twin-twin transfusion syndrome. The indications for delivery were as follows: 8 patients for non-reassuring nonstress tests, two patients for preterm labor, two patients delivered electively with mature lung profile and one patient with intrauterine growth retardation. The combined literature review revealed 202 sets of monoamniotic twins. This included 58 sets that had prenatal diagnosis, with outcomes available in 52 sets and overall perinatal survival in 82 of 104 infants (79%). In the group that did not have accurate prenatal diagnosis (77 sets), perinatal survival occured in 101 of 154 infants (66%). The remaining 67 sets had no mention of whether prenatal diagnosis was made.

These authors showed a marked reduction in perinatal mortality due to accurate prenatal diagnosis and careful and frequent antenatal testing. It is uncertain what the right frequency of testing for this condition is, however it appears that a minimum of 2-3 times per week is necessary. These authors presently deliver all of these cases by cesarean section, deliver either at fetal lung maturity or 35 weeks (whichever comes sooner) and administer weekly antenatal corticosteroids beginning at 24-26 weeks gestation.

Differential Diagnosis:

Twin pregnancy in which the membrane could not be identified. Female and male genitalia (arrows) mean the pregnancy must be dizygotic and diamniotic

A true or false knot in the umbilical cord of one twin may simulate intertwined cords. Identification of the dividing membrane will help differentiate these entities. The dividing membrane, particularly when thin, may not be seen for techinical reasons. Identification of opposite sexes of the fetuses means the pregnancy must be diamniotic whether the membrane is seen or not. An anterior abdominal wall defect, such as a gastroschisis, with extruded bowel in the amniotic cavity may simulate two umbilical cords.

References:

Quigley JK. Monoamniotic twin pregnancy-a case record with review of the literature. Am J Obstet Gynecol 29:354-62,1935

Tessen JA, Zlatnik FJ. Monoamniotic twins: a retrospective controlled study. Obstet Gynecol 77:832, 1991

Carr SR, Aronson MP, Coustan DR. Survival rates of monoamniotic twins do not decrease after 30 weeks gestation. Am J Obstet Gynecol 163:719-722, 1990

Blane CE, DiPietro MA, Johnson MZ, White SJ et al. Sonographic detection of monoamniotic twins. J Clin Ultrasound 15:394-396,1987

Bhakthavathsalan A, Heinz L, Wafalosky J, Armstrong CL and Kirkhope TG. Ultrasound diagnosis of monoamniotic twins with cord entanglement: case report with double survival. J Clin Ultrasound 13:137-140, 1985

Nyberg DA, Filly RA, Golbus MS, Stephens JD. Entangled umbilical cords: a sign of monoamniotic twins. J Ultrasound Med 3:29-32, 1984

Gilbert WM, Davis SE, Kaplan C, Pretorius D, Merritt TA, Bernirschke K. Morbidity associated with prenatal disruption of the dividing membrane in twin gestations. Obstet Gynecol 78:623, 1991

Rodis JF, McIlveen PF, Egan JFX, Borgida AF, Turner GW, Campbell WA. Monoamniotic twins: Improved perinatal survival with accurate prenatal diagnosis and antenatal fetal surveillance. Am J Obstet Gynecol 177:1046-9, 1997

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California