Circulating free soluble fms-like tyrosine kinase-1 during late first trimester in relation with placental volume as a surrogate for trophoblastic production: a physiology study in low-risk cohort.

BACKGROUND: Data on first-trimester circulating soluble fms-like tyrosine kinase-1 (sFlt-1) and ischemic placental disease is limited and conflicting. This study aimed to study its physiology in relation to trophoblastic mass as the source of production.

METHODS: Low-risk (representing normal placentation) women from 11 0/7 to 13 6/7 weeks' gestation were prospectively enrolled. Selective measurement of serum free sFlt-1 using a new automated assay from 100 eligible subjects was analyzed with gestational age, maternal weight, fetal crown-rump length (CRL), and mean uterine artery Doppler pulsatility index (PI). Placental volume (surrogate for trophoblastic mass) was estimated using 3-dimensional ultrasound and was assessed for its association with serum free sFlt-1.

RESULTS: There was no significant association between serum free sFlt-1 and placental volume in either arithmetic (r = 0.053, p = 0.600), logarithmic (r = 0.005, p = 0.963), or quartile (p = 0.703) scale. There was a significant negative correlation between free sFlt-1 level and maternal weight (r=-0.213, p = 0.033). No significant correlation was found between free sFlt-1 level and gestational age (r = 0.007, p = 0.947), CRL (r = 0.027, p = 0.788), and uterine artery Doppler mean PI (r = 0.020, p = 0.828).

CONCLUSIONS: Lack of correlation between circulating free sFlt-1 level and placental volume suggests that trophoblasts are not its major source during first trimester with presumably physiologic placentation.