Interventions developed during the past three decades have dramatically altered the course of selected fetal anomalies and conditions. Reviewed in this chapter are fetal disorders amenable to treatment with either maternal medication or surgical procedures. The treatment of fetal anemia and thrombocytopenia is reviewed in Chapter 15, and the treatment of some fetal infections is discussed in Chapters 64 and 65.
Fetal pharmacotherapy, administered to the mother and transported transplacentally, can be used to treat an array of serious conditions. Two well-described examples are fetal tachyarrhythmia treatment with medications such as digoxin, and corticosteroid therapy to prevent virilization of female fetuses with congenital adrenal hyperplasia. More recently, a course of corticosteroid therapy—the same used to promote lung maturity before preterm birth—has been used to stabilize the growth of large fetal lung masses and avoid fetal surgery.
Fetal cardiac rhythm disturbances may be broadly categorized as tachyarrhythmias, heart rates > 180 beats per minute (bpm); bradyarrhythmia, heart rate < 110 bpm; and ectopy, typically premature atrial contractions. Fetal M-mode sonography (Bradyarrhythmia) should be performed to determine the atrial and ventricular rate to clarify the relationship between atrial and ventricular beats, thereby diagnosing the rhythm disturbance type.
Premature Atrial Contractions
This is by far the most common arrhythmia. Premature atrial contractions are identified in 1 to 2 percent of pregnancies and are generally a benign finding (Hahurij, 2011; Strasburger, 2010). They represent immaturity of the cardiac conduction system and typically resolve either with advancing gestation or in the neonatal period. Although they may be conducted, they are more commonly blocked, and with handheld Doppler or fetoscope, they sound like a dropped beat. Premature atrial contractions are not associated with major structural cardiac abnormalities, but they sometimes occur with an atrial septal aneurysm. As shown in Figure 10-24 (M-Mode), M-mode evaluation demonstrates that the dropped beat is a compensatory pause following the premature atrial contraction. They may occur as frequently as every other beat, known as blocked atrial bigeminy. This results in an auscultated fetal ventricular rate as low as 60 to 80 beats per minute. Unlike other causes of bradycardia, this carries a benign prognosis and does not require treatment (Strasburger, 2010).
Approximately 2 percent of fetuses with premature atrial contractions are later identified to develop supraventricular tachycardia (SVT) and require urgent treatment to prevent development of hydrops (Copel, 2000; Srinivasan, 2008). Given the importance of identifying such tachycardia, the fetus with premature atrial contractions is often monitored with heart rate assessment every 1 to 2 weeks until ectopy resolution.
The two most common are supraventricular tachycardia and atrial flutter. SVT is characterized by an abrupt increase in the fetal heart rate to 180 to 300 bpm with 1:1 atrioventricular concordance. The typical range is 200 to 240 ...