LOW-LEVELS OF AMNIOTIC-FLUID PLACENTAL ALKALINE-PHOSPHATASE IN DOWNS-SYNDROME

Objective To investigate amniotic fluid placental alkaline phosphatase (PLAP) levels in normal and trisomy 21 pregnancies. Design Cross sect ional study. Setting A tertiary referral prenatal diagnostic service. Subjects Three hundred and eleven women with singleton pregnancies of normal karyotype between 10 and 23 weeks gestation and 31 women with p regnancies associated with trisomy 21 Down's syndrome. Outcome measure s PLAP levels were measured by immunoradiometric assay in amniotic flu id obtained by amniocentesis. Results Amniotic fluid PLAP was detectab le from 12 weeks gestation and the median value rose to a peak of 4.57 iu/l at 18 weeks. Pregnancies associated with Down's syndrome had sig nificantly lower levels with a median multiple of median (MoM) of 0.63 8, (U = 3374, P = 0-0016, 95% CI = 0.50, 0.89). For the 20 women with trisomy 21 pregnancies detected at 16 to 18 weeks, the median MoM was 0.482, (U = 3694, P = 0.0011, 95% CI = 0.37,0.85). Conclusion These da ta demonstrates that PLAP levels are reduced in the amniotic fluid of women carrying a fetus with trisomy 21.