Iodide concentrations in matched maternal serum, cord serum, and amniotic fluid from preterm and term human pregnancies

OBJECTIVES: To characterize the matched maternal and cord plasma and the amniotic fluid concentrations of iodide in preterm and term human pregnancies. METHODS: Specimens were collected at the delivery of 121 singleton pregnancies (92 at term, 29 preterm) with no pre-existing medical complications. Plasma unbound iodide concentrations were measured by the difference between the protein bound iodine and the total iodine measured spectrophotometrically. Total iodide was measured in amniotic fluid. RESULTS: Maternal plasma iodide concentrations were 1.6 +/- 0.4 mcg/dL (mean +/- S.D.) for preterm deliveries and 1.5+/ -0.5 mcg/dL for term deliveries. Cord plasma iodide concentrations were 1.4 +/- 0.5 mcg/dL for preterm deliveries and 1.7 +/- 0.7 mcg/dL for term deliveries. Cord plasma iodide concentrations at birth correlated highly with maternal levels (p < 0.001). The cord:maternal plasma iodide ratio for all pairs was 1.2+/- 0.7. The average cord:maternal plasma iodide ratio was not significantly different between the preterm (0.9+/- 0.4) and term (1.3+/- 0.8) deliveries. Amniotic fluid iodide concentrations did not correlate significantly with cord plasma concentrations. CONCLUSION: Cord plasma concentrations of iodide correlate with paired maternal levels, indicating that, unlike the rabbit and other species, the human conceptus does not highly concentrate iodide.