Dramatic increase in levels of placental protein 14 in amniotic fluid at 10-15 weeks' pregnancy.

Concentrations of placental protein 14 (PP14) were measured by radioimmunoassay in 103 amniotic fluid samples from 10 to 20 weeks of pregnancy. Low levels of PP14 were present at 10-12 weeks (median values 82-280 micrograms/l). After 12 weeks, the levels increased by two orders of magnitude to reach a peak at 18 weeks (median 11 mg/l). This pattern may reflect the obliteration of the extraembryonic coelom and direct apposition of the decidua with the chorio-amnion.