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KEY POINTS

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Key Points

  • Third most common liveborn autosomal aneuploidy. Incidence is approximately 1 in 5000 livebirths.

  • Sonographic findings include holoprosencephaly, abnormal midface, congenital heart defects, polydactyly, and echogenic kidneys. First trimester findings include increased nuchal translucency measurement, fetal tachycardia, and early onset growth restriction.

  • Differential diagnosis includes pseudotrisomy 13, Meckel–Gruber syndrome, Bardet–Biedl syndrome, and Smith–Lemli–Opitz syndrome.

  • Associated with increased lethality in utero, and increased incidence of preeclampsia.

  • 80% of patients have full trisomy 13; 20% have mosaicism or a translocation. If a translocation is demonstrated, parental chromosomes should be studied.

  • Prognosis is uniformly poor. Median survival time is 7 to 10 days. Five to 10% of patients survive up to one year of age.

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CONDITION

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Trisomy 13 presents as constellation of congenital anomalies that result from the presence of an extra chromosome 13, either whole or translocated onto another chromosome. It is not known how the presence of the extra chromosome disrupts so many different systems during organogenesis.

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Although the clinical findings of the condition were previously known, the association of the extra chromosome with the clinical syndrome was not described until 1960 (Patau et al., 1960). Synonyms for trisomy 13 include trisomy D or Patau syndrome.

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INCIDENCE

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Trisomy 13 is the third most common liveborn autosomal aneuploidy. The incidence of trisomy 13 has been variously reported as 1 in 2206 to 1 in 7602 livebirths (Taylor, 1968). Most authors give the approximate incidence figure of 1 in 5000 livebirths (Wladimiroff et al., 1989). The incidence of trisomy 13 is equal among all races. It is thought that there are equal numbers of conceptuses of both genders. However, a slight excess of females exists at birth presumably due to a survival advantage (Jacobs et al., 1987).

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SONOGRAPHIC FINDINGS

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Fetuses with trisomy 13 are more active in utero than comparable fetuses with trisomy 18. In addition, fetuses with trisomy 13 have a higher frequency of major congenital anomalies than fetuses with trisomy 21. The most common major abnormality seen in trisomy 13 is holoprosencephaly, which can be seen as early as 12 weeks of gestation (Figure 129-1). Other important findings associated with trisomy 13 include an abnormal midface with hypotelorism, cleft lip or palate, and even cyclopia (see Chapter 14) (Figure 129-2). Many studies have shown that there is a greatly increased incidence of congenital heart disease in fetuses affected with trisomy 13 (Wladimiroff et al., 1995). The most common cardiac defects include ventricular septal defect (VSD), hypoplastic left ventricle, or double outlet right ventricle. Other common sonographic findings include ulnar/fibular polydactyly and echogenic or polycystic kidneys. In one study, all fetuses with trisomy 13 had one or more sonographic abnormalities or abnormal measurements present (Seoud et al., 1994).

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