WordNet (r) 3.0 (2006):

birth defect
    n 1: a defect that is present at birth [syn: birth defect,
         congenital anomaly, congenital defect, congenital
         disorder, congenital abnormality]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "birth defect":
   abnormality, acute disease, affection, affliction, ailment,
   allergic disease, allergy, atrophy, bacterial disease, blight,
   cardiovascular disease, chronic disease, circulatory disease,
   complaint, complication, condition, congenital defect, defect,
   deficiency disease, deformity, degenerative disease, disability,
   disease, disorder, distemper, endemic, endemic disease,
   endocrine disease, epidemic disease, functional disease,
   fungus disease, gastrointestinal disease, genetic disease,
   handicap, hereditary disease, iatrogenic disease, illness,
   indisposition, infectious disease, infirmity, malady, malaise,
   morbidity, morbus, muscular disease, neurological disease,
   nutritional disease, occupational disease, organic disease,
   pandemic disease, pathological condition, pathology, plant disease,
   protozoan disease, psychosomatic disease, respiratory disease,
   rockiness, secondary disease, seediness, sickishness, sickness,
   signs, symptomatology, symptomology, symptoms, syndrome, the pip,
   urogenital disease, virus disease, wasting disease, worm disease