Amniotic fluid S100B protein in mid-gestation and intrauterine fetal death

Fetal death in the mid-trimester of pregnancy is unexplained and no reliable markers are available to identify at-risk women. We aimed to assess use of alpha fetoprotein and S100B concentrations in amniotic fluid as markers. We did a case-control study in 758 healthy women undergoing amniocentesis at mid-gestation, of whom 12 had a spontaneous intrauterine fetal death before 28 weeks, and 746 matched controls. Concentrations were corrected for gestational age by conversion to multiples of median (MoM) of healthy controls of the same gestational age. Concentrations of S100B, but not alpha fetoprotein, were significantly higher (p<0.0001) in women who later had spontaneous fetal death (median 4.431 MoM [95%CI 3.605-6.197]) than in controls (1.000 MoM [1.062-1.121]). Sensitivity, specificity, and positive and negative predictive values of S100B as a diagnostic test were 100%, suggesting that measurement of this protein at amniocentesis could be useful to identify at-risk women.