 The first specific aim is to determine if women with highly skewed X chromosome inactivation are at risk of pregnancy loss. This will be accomplished through a prospective protocol, analyzing X chromosome inactivation patterns in pregnant women and investigating a possible association between X chromosome inactivation and pregnancy outcome. The second aim will study the nature of pregnancy loss in women with skewed X chromosome inactivation. This aim will correlate maternal X inactivation patterns with abortus karyotype. 