The incidence of conjoined twins is estimated to range from 1 in 50 000 to 1 in 100 000 births1. The most common types of conjoined twins are thoracopagus, omphalopagus and thoraco-omphalopagus1. Only about 12% are of the ischiopagus variety2, which refer to twins joined at the level of the ischium.
A 30-year-old woman, gravida 2, para 1, was seen at our antenatal clinic during her 9th week of pregnancy. She denied exposure to ovulation medication prior to conception. Two-dimensional (2D) ultrasonography revealed monoamniotic twins lying face-to-face, one yolk sac (Figure 1) and two separate cardiac pulsations. The embryos were fused at the lower part of the trunk and were suspected to be twins conjoined at the level of the pelvis. Subsequently, a three-dimensional (3D) volume dataset of the embryos was acquired using transvaginal ultrasonography with power Doppler (Voluson 730 Expert, GE Medical Systems, Milwaukee, WI, USA). Vascular communication between the conjoined twins in the pubic area was accurately delineated (Figure 2). A volume dataset was acquired in the sagittal plane for subsequent analysis. The multiplanar views and surface-rendered images of the embryos were obtained to precisely delineate the level of fusion, connecting vessels and fetal contour (Figure 3). One week later, repeat scans by 3D transvaginal ultrasonography confirmed the diagnosis of conjoined twins. After counseling, the patient opted to terminate the pregnancy. After evacuation, two separate bodies and two separate upper and lower extremities were noted. The location of the conjoined site could not be identified on gross inspection of the abortus because the embryos had been destroyed during the evacuation procedure.
Early diagnosis of conjoined twins is crucial for determining subsequent management and possibly decreasing maternal morbidity (evacuation vs. hysterotomy). Specific sonographic findings of conjoined twins examined during the first trimester include inseparable fetal bodies despite manipulation of the uterus with a transvaginal probe or prolonged continuous scanning, bifid appearance of the embryo, single yolk sac3, and a single umbilical cord with more than three vessels. Recently, some reports4–8 have described early diagnosis of conjoined twins by 3D ultrasound imaging combined with power Doppler, computed tomography and magnetic resonance imaging.
In this case, prenatal diagnosis of conjoined twins was established by transvaginal 2D ultrasonography and power Doppler. However, 3D imaging with surface-rendering provided clearer images of the characteristic features of ischiopagus twins and helped the parents to understand the complex anomalies present in their fetuses. Furthermore, it improved our diagnostic confidence to provide adequate early intervention.