In the absence of any prenatal screening, some two percent of babies will be born with a structural anomaly; a further 1 in 700–800 will be born with Down's syndrome, with similar numbers having other chromosomal and serious genetic disorders. The prevalence of abnormalities in early pregnancy is higher because abnormal fetuses are more likely to miscarry than normal ones. A small number of women enter pregnancy at increased risk of conceiving a baby with an abnormality. They may have a maternal condition such as diabetes, need medication for conditions such as epilepsy, or have a family history of a genetic disorder (www3.ncbi.nlm.nih.gov/Omim/searchomim.html). Most abnormalities, however, occur in healthy, low-risk women.