Umbilical cord entanglement in monoamniotic twins.

Abstract

Monochorionic–monoamniotic twin pregnancies are a rare obstetric high-risk situation with an estimated frequency of 1 per 25 000 pregnancies. They occur when the division of the morula into two similar totipotent parts takes place between days 9 and 12 after conception. Perinatal mortality is extremely high, ranging between 28% and 70%1. Fetal mortality is caused by prematurity, cord complications and associated congenital anomalies. These days, with the widespread application of sophisticated first-trimester ultrasound, the detection of monoamniotic twin pregnancies can occur earlier and be more precise. Sonographic criteria include single placenta, absence of separating membrane and concordant sex. However, this improved diagnosis has little impact on the regime of surveillance, management and outcome of such pregnancies. While intensive surveillance of monoamniotic twin pregnancies is generally performed, the right time for and mode of delivery are still under discussion. Delivery by Cesarean section at 32 weeks' gestation is recommended by some groups2 in order to avoid intrauterine complications in late pregnancy. However, whether there is excess mortality after 30–32 weeks is questionable. A recent study by Demaria et al.3 of 19 monoamniotic twin pregnancies documented that there were no double fetal deaths after 26 weeks. Delivery of monoamniotic pregnancies by Cesarean section can also help avoid intrapartum accidents of collision and impaction. However, Demaria et al.3 report a 40% rate of uncomplicated vaginal deliveries. The Picture of the Month (Figure 1a) demonstrates prenatal color Doppler imaging of a monoamniotic twin pregnancy in week 26 showing the two very close cord insertions. Under strict surveillance the pregnancy was successfully continued until week 32. Two healthy newborns were delivered via primary Cesarean section after systematic pulmonary maturation. Part (b) illustrates the large umbilical cord entanglement with a very short section of ‘free’ cord in both twins. In this case a cord accident with a tight clinch and entanglement with impaired umbilical perfusion seems probable if the pregnancy had been prolonged. Furthermore, this situation excludes a normal vaginal delivery. In retrospect, a planned Cesarean section in the 32nd week was justified since both newborns showed a normal neonatal adaptation period. (a) Prenatal color Doppler ultrasound image of a monoamniotic twin pregnancy in week 26 showing the two very close cord insertions. (b) Postnatal photograph showing the large umbilical cord entanglement (black arrows) with a very short section of ‘free’ cord (white arrow) in both twins. Knowing that no optimal protocol for the management of monoamniotic pregnancies has been defined, we believe that sonographic investigation and documentation of the umbilical cord may contribute helpful information to the decision-making process.