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Minor grades of hydramnios rarely require active treatment. On the other hand, when the abdomen is immensely distended and respiration is seriously hampered, the termination of pregnancy is urgently indicated. In such cases, the symptoms can be promptly relieved by perforating the membranes through the cervix, after which the amniotic fluid drains off and labour pains set in.
—J. Whitridge Williams (1903)
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The concept of fetal therapy—even amniocentesis—was not considered by Williams in his first edition. Aside from a few destructive procedures to aid vaginal delivery, any type of fetal treatment is not mentioned as even a remote possibility. Again, fast forward to this 25th edition, when 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 management of fetal anemia and thrombocytopenia is reviewed in Chapter 15, and treatment of some fetal infections is discussed in Chapters 64 and 65.
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Fetal pharmacotherapy uses medications administered to the mother and then transported transplacentally to the fetus. As described here, it can be used to treat an array of serious conditions.
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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. If these are identified, fetal M-mode sonography is performed to measure the atrial and ventricular rates and to clarify the relationship between atrial and ventricular beats, thereby diagnosing the type of rhythm disturbance.
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Premature Atrial Contractions
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This is by far the most common arrhythmia and is identified in 1 to 2 percent of pregnancies (Hahurij, 2011; Strasburger, 2010). Generally a benign finding, premature atrial contractions represent immaturity of the cardiac conduction system, and they typically resolve later in gestation or in the neonatal period. If the premature atrial contraction is conducted, it sounds like an extra beat when auscultated with handheld Doppler or fetoscope. However, premature atrial contractions are more commonly blocked and sound like dropped beats.
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In general, premature atrial contractions are not associated with major structural cardiac abnormalities, although they sometimes occur with an atrial septal aneurysm. As shown in Figure 10-34, 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 bpm. Unlike other causes of bradycardia, atrial bigeminy is benign and does not require treatment (Strasburger, 2010).
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Approximately 2 percent of fetuses with premature atrial contractions are later found to have a supraventricular tachycardia (...