Soluble Fas and Fas-ligand levels in mid-trimester amniotic fluid and their associations with severe small for gestational age fetuses: a prospective observational study.

We aimed to determine the second-trimester amniotic fluid (AF) levels of soluble Fas (sFas) and Fas-ligand (FasL) and investigate their association with fetal growth. Therefore, sFas and FasL levels were measured by enzyme immunoassay in the AF of 21 small for gestational age (SGA), 13 large for gestational age (LGA), and 44 appropriate for gestational age (AGA) fetuses of pregnant women who underwent amniocentesis at between 15 and 22 weeks gestation. Our study results showed that sFas and FasL levels were detectable in AF. sFAS median (25th-75th centile) levels were 3.8 (2.8-4.6) ng/ml in SGA, 3.6 (3.1-4.5) ng/ml in AGA, and 4.0 (3.1-4.4) ng/ml in LGA. FasL median (25th-75th centile) levels were 26.0 (20.3-32.7) pg/ml in SGA, 22.7 (18.4-28.5) pg/ml in AGA, and 21.5 (15.8-30.9) pg/ml in LGA. The differences were not statistically significant. Nevertheless, statistically significant differentiation of FasL levels existed when SGA fetuses in the extremes of distribution (≤5th, ≤2.5th centile) were considered. This is the first study presenting sFas and FasL concentrations in early second-trimester amniotic fluid in AGA, SGA, and LGA fetuses. We found indications that severe and very severe SGA fetuses (≤5th and ≤2.5th centile) have high levels of FasL in the amniotic fluid. This finding probably reflects the increased rate of apoptosis that is assumed to exist in cases of extreme growth restriction.