S100B Protein Concentrations in Amniotic Fluid Are Higher in Monoamniotic than in Diamniotic Twins and Singleton Pregnancies

S100B is an acidic calcium-binding protein of the EF-hand family present in the central nervous system, where it is located mainly in glial cells (1). It has been suggested that the protein is involved in various cellular functions, but precisely which is still a matter of debate. The protein has been found to act at physiologic concentrations as a cytokine with a neurotrophic role in experimental models, in cell cultures, and in biological fluids such as cord blood, peripheral blood, and urine (1)(2)(3)(4). This hypothesis has been corroborated by measurements of S100B protein in amniotic fluid in the second trimester of pregnancy (5). The present work, following from an earlier study, investigates amniotic fluid S100B concentrations in twins.We performed a case-control study (between January 1998 and June 2002) of 49 women with physiologic twin pregnancies (27 monoamniotic and 22 diamniotic) who underwent amniocentesis to exclude chromosomal abnormalities between the 15th and 18th weeks of gestation (mean, 16.5 weeks). The control group consisted of 490 singleton pregnancies matched for gestational age and weight at sampling and normal neonatal outcome (5 control fetuses for each twin fetus). Appropriate fetal growth was defined by the presence of ultrasonographic signs (when biparietal diameter and abdominal circumference were between the 10th and 90th percentiles) according to the normograms of Campbell and Thoms (6) and by postnatal confirmation of a birth weight between the 10th and 90th percentiles according to our population standards after correction for maternal height, weight, and parity and the sex of the newborns. Exclusion criteria included intrauterine growth retardation; gestational hypertension; diabetes and infections; fetal malformations; chromosomal abnormalities; maternal exposure to alcohol, cocaine, or smoke; perinatal asphyxia; and dystocia.The local ethics committee approved the study protocol, and the parents of the fetuses examined gave …