Interpretation of urinary oestrogen:creatinine ratio for monitoring fetoplacental function in late pregnancy.

In pregnancies with a normal outcome the oestrogen:creatinine ratio in early morning samples of urine showed a smaller day-to-day variation than the ratio in 24-h urine or the 24-h total oestrogen excretion, and a significant fall could be detected more easily. Patients admitted to hospital who eventually delivered a healthy baby provided a reference range which, after logarithmic transformation, increased linearly with period of gestation. A fall in log10 oestrogen:creatinine ratio exceeding 40% of this range is unusual in pregnancies with a healthy outcome, and suggest impaired fetoplacental function.