Haas D 1 , Hoffmann GF 1 , Burgard P 1 1 Div Inb Metab Dis, Univ Children's Hosp, Heidelberg, Germany Background: Smith-Lemli-Opitz syndrome (SLOS) is a multiple malformation syndrome due to a deficiency of 7-dehydrocholesterol reductase resulting in an accumulation of 7-and 8-dehydrocholesterol in serum and amniotic fluid (AF). In affected pregnancies free estriol is often reduced and in prenatal ultrasound intrauterine growth retardation (IUGR) and malformations of CNS, heart, kidney, genitals and limbs are often detected. Objectives: Evaluating the specificity of features leading to a suspicion of fetal SLOS. Material and Methods: From 2002 to 2011 we determined sterol concentrations in AF samples from 69 pregnancies suspicious for SLOS by gas chromatography mass spectrometry. Results: Sterol analysis in AF was done in 24 cases because of the family history (affected sibling: n=14, other affected family member: n=5, lethal malformations in a sibling: n=5). In 39 cases prenatal abnormalities were determined (reduced estriol: n=10, multiple fetal malformations: n=15, IUGR: n=11). In 6 cases there was no clinical information. SLOS was diagnosed in 6 fetuses (8.7 %). 3 of those had an affected sibling, 3 had multiple malformations, one additionally a reduced estriol concentration. Conclusion/Discussion: The highest rate of confirmed SLOS was in at risk families, whereas fetal malformations were in most cases not caused by SLOS.