Viable term pregnancy despite "subluteal" serum progesterone levels in the first trimester.

This is a report of a 34-year-old patient with a 3-year history of unexplained infertility, who conceived after IVF-ET. Her serum P levels were < 2.0 ng/mL (conversion factor to SI unit, 3.180) between 5 and 6 weeks of gestation. She subsequently delivered a viable infant at term.