Acardia Health Article

Diagnosis

A mother carrying an acardiac twin pregnancy is not likely to have any unusual symptoms. An acardiac twin is most often found incidentally on prenatal ultrasound. No two acardiac twins are formed exactly alike, so they may present differently. During ultrasound, an acardiac twin may appear as tissue mass or it may appear to be a twin who has died in the womb. Acardia is always suspected when, on ultrasound, a twin once considered to be dead begins to move or grow, or there is visible blood flow through that twin's umbilical cord. In 50% of cases the acardiac twin has only two, instead of the normal three, vessels in the umbilical cord. A two vessel umbilical cord may also be found in some normal pregnancies.

Ultrasound diagnostic criteria for the acardiac twin usually include:

• absence of fetal activity
• no heart beat
• continued growth
• increasing soft tissue mass
• undergrowth of the upper torso
• normal growth of the lower trunk

An acardiac fetus may also be missed on prenatal ultrasound. A 1991 report describes an acardiac twin who was missed on ultrasound and only detected at delivery. In rare cases a diagnosis of acardia is not possible until autopsy.

Treatment and management

As of 2001, there is no consensus on which therapy is best for pregnancies complicated by TRAP sequence. No treatment can save the acardiac twin, so the goal of prenatal therapy is to help the normal twin. The normal twin is not always saved by prenatal treatment.

Specialists have used laser and electrical cauterization, electrodes, serial amniocentesis, medications, and other treatments successfully. Physicians often recommend prenatal interruption of the blood vessel connections (thus sacrificing the acardiac twin) before heart failure develops in the pump twin.

Cutting off blood circulation to the acardiac twin can be accomplished by cauterizing or burning the blood vessel connections. In a 1998 study of seven pregnancies treated with laser therapy the rate of death in the normal twin was 13.6%, a vast improvement over the expected 50% death rate. Medications like digoxin may be used to treat congestive heart failure in the normal twin. Current studies examining the success and failure rates of these treatments will be helpful in determining which therapy is the best option.

Fetal echocardiography is recommended to assist with early detection of heart failure in the normal twin. Chromosome studies are recommended for both fetuses in all pregnancies complicated by TRAP sequence.

Prognosis

The acardiac or parasitic twin never survives as it is severely malformed and does not have a functioning heart. Complications associated with having an acardiac twin cause 50–70% of normal twins to die. The normal twin is at risk for heart failure and complications associated with premature birth. Heart failure in the normal twin is common. The normal twin of an acardiac twin pregnancy has about a 10% risk for malformations. Therapy is thought to decrease the normal twin's risk for heart failure and premature birth. Improvement of therapies will undoubtedly lead to a better outlook for pregnancies complicated by TRAP sequence.

PERIODICALS

Arias, Fernando, et al. "Treatment of acardiac twinning." Obstetrics & Gynecology (May 1998): 818-21.

Brassard, Myriam, et al. "Prognostic markers in twin pregnancies with an acardiac fetus." Obstetrics and Gynecology (September 1999): 409-14.

Mohanty, C., et al. "Acardiac anomaly spectrum." Teratology 62 (2000): 356-359.

Rodeck, C., et al. "Thermocoagulation for the early treatment of pregnancy with an acardiac twin." New England Journal of Medicine 339 (1998): 1293-95.

ORGANIZATIONS

Twin Hope, Inc. 2592 West 14th St., Cleveland, OH 44113. (502) 243-2110. <http://www.twinhope.com>.

Judy C. Hawkins, MS