References for: Causes, evaluation, and treatment.

Medscape Women's Health 1998 May;3(3):2 (ISSN: 1521-2076)
Bick RL; Madden J; Heller KB; Toofanian A

Thrombosis Clinical Center, Department of Medicine (Hematology & Oncology),
Presbyterian Hospital of Dallas, Tex., USA.

Impact and Implications of Chromosomal Abnormalities

Relationship to Spontaneous Abortion

Chromosomal anomalies are known to be the single most common cause of spontaneous abortion. Historically, 50% of spontaneously expelled abortuses have been thought to be chromosomally abnormal.[1]However, this is probably an underestimate in light of recent improvements in tissue culture techniques, coupled with earlier diagnosis of miscarriage.[2] In spontaneous abortions, the majority of chromosomal anomalies (95%) are numerical. About 60% are trisomies, trisomy 16 being the most common (see Fig. 2).[1] A further 20% are found to have 45,X (Turner's syndrome).[1]Interestingly, approximately 99% of fetuses with 45,X are expelled spontaneously.[3] Another 15% have polyploidy, especially triploidy (see Fig. 3).[1]

Figure 3. Karyotype of 69,XXY (triploidy), common finding in spontaneous abortion. Risk for chromosomal anomaly in subsequent pregnancy is not increased significantly.

In the case of a numerical chromosomal anomaly in a fetus, parental chromosomes are usually normal, so karyotype analysis of the parents is not indicated. The recurrence risk for a chromosomal anomaly following the diagnosis of trisomy in a pregnancy is thought to be about 1%.[1,4]

After diagnosis of a numerical chromosomal anomaly, couples should be counseled about the 1% risk for recurrence of a numerical anomaly, and prenatal diagnosis of the fetus may be considered for any future pregnancies. On the other hand, if a structural chromosomal anomaly is found in a fetus, parental karyotypes are indicated. The presence of a balanced chromosomal rearrangement in a parent would result in an increased recurrence risk for structural chromosomal defects in future pregnancies.

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