Conjoined Twins Workup

Updated: Feb 03, 2016
  • Author: Khalid Kamal, MD, MBBS, FAAP, FCPS, MCPS; Chief Editor: Robert K Minkes, MD, PhD  more...
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Laboratory Studies

Chromosomal studies are inconclusive. An abnormal X-chromosome inactivation has been proposed, but this has not been proven.

Amniocentesis with an estimation of the lecithin-sphingomyelin ratio is performed to assess fetal lung maturity and to determine the optimal time for a cesarean delivery.


Imaging Studies

Prenatal ultrasonography can reveal conjoined twinning as early as 8 weeks' gestation. Conversely, twins with extreme fusion may be mistaken for a singleton. The twin fetuses do not move apart with fetal movement. Polyhydramnios is frequent (75%). A monoamniotic cavity is present, and more than 3 umbilical vessels may be observed. Fusion sites include the thorax (thoracopagus), abdomen (omphalopagus), pelvis (ischiopagus), sacrum (pygopagus), or skull (craniopagus). Extensive zones of fusion may be named by the prefix di- (meaning 2), followed by the portion of the twins that is unfused. Examples include dicephalus (2 heads on one body), and dipygus (double buttocks; single head and torso with separate pelves and 4 legs). Serial scans may be required to monitor for hydrops.

Prenatal echocardiography has better yield than postnatal echocardiography in thoracopagus twins, because surface scanning may be difficult.

MRI of the brain is performed along with magnetic resonance angiography and magnetic resonance venography to delineate structures and blood supply in the craniopagus variety.

Radionuclide angiography is performed to calculate the extent of cross-circulation. Selective angiography is usually not necessary in twins with a shared liver.

Sonography allows for a complete anatomic examination and search for associated lethal malformations. A detailed ultrasound examination to exclude the possibility of conjoined twins is mandatory in all multiple pregnancies. Two-dimensional ultrasonography is instrumental in prenatally diagnosing conjoined twins, but precise classification is difficult because of 3-dimensional structures. Three-dimensional ultrasound has shown promise in improving the visualization of complex anatomic spatial relationships. Abdominal ultrasonography is performed to determine how many gallbladders are present (1 or 2) and to determine the polarity of the liver and pancreas if these organs are also conjoined. Often, however, this determination may not be precise.

Advantages of sonography include the following:

  • Images other structures (eg, aorta, pancreas, liver)
  • Identifies complications (eg, stenosis, obstruction)
  • Can be rapidly performed at the bedside
  • Does not involve radiation (important in pregnancy)

Disadvantages of sonography include the following:

  • Dependent on the type and extent of fusion, as well as the operator's abilities
  • Inability to image the ductal system proximal to the common bile duct
  • Decreased sensitivity for the site and extent of duplication or fusion compared with CT scanning or MRI.

Fetal MRI can identify shared anatomy of twins with precise detail. However, this test is not 100% accurate.

CT scanning has been used in some studies. [26] However, the yield for complex anatomy is lower than that obtained from MRI. CT scanning may be helpful in shared bony pelvis and shared pelvic perineal muscles.

Contrast studies are performed to evaluate the extent of GI (see the image below), genitourinary, and reproductive system fusions.

Esophagram showing union at the level of stomach. Esophagram showing union at the level of stomach.

Diisopropyl iminodiacetic acid (DISIDA) scanning is a nuclear medicine study performed to visualize the biliary tract. Technetium-labeled analogue of DISIDA is administered intravenously (IV) and is secreted by hepatocytes into bile, enabling visualization of the gall bladder and biliary tree in 30 minutes.


Other Tests

On ECG, a single QRS indicates that cardiac separation is not possible. However, the presence of 2 separate patterns does not guarantee a successful separation.

EEG may be performed to evaluate baseline brain activity in craniopagus twins.


Diagnostic Procedures

Cardiac catheterization is performed to determine the nature of complex cardiac anomalies. An accurate estimation of all major inflow and outflow vessels should be made.