BACKGROUND:

Knowledge is limited of how estrogen and progesterone variability in fertile women are associated with achieving pregnancy.

METHODS:

From 1996 to 1998, we enrolled 347 textile workers without hormone treatment in Anhui, China, who provided daily urine and data upon stopping contraception for up to 1 year until clinical pregnancy. Urinary hCG was assayed to detect conception and early pregnancy losses. We compared urinary concentrations of estrone conjugates (E(1)C) and pregnanediol-3-glucuronide (PdG) in 266 clinical pregnancies, 63 early pregnancy losses and 272 non-conception cycles from 347 women and also in 94 clinical pregnancy and 94 non-conception cycles from the same women.

RESULTS:

Using generalized estimating equations and relative to 266 clinical pregnancy cycles, log(E(1)C) was lower in 272 non-conception cycles [beta = -0.3 ng/mg creatinine (Cr); SE = 0.1; P < 0.0001]. On average, daily E(1)C was 18 ng/mg Cr lower in non-conception cycles than in clinical pregnancy cycles. Relative to 94 clinical pregnancy cycles, log(E(1)C) was lower in 94 non-conception cycles (beta = -0.4 ng/mg Cr; SE = 0.1; P < 0.0001) from the same women (average difference in daily E(1)C was 20 ng/mg Cr). The odds of E(1)C less than the 10th percentile (<30 ng/mg Cr) were higher in early pregnancy loss cycles [odds ratio (OR) = 4.8; P = 0.0027] than in clinical pregnancy cycles in the early luteal phase. Compared with clinical pregnancy cycles, log(PdG) concentrations were lower in non-conception cycles during the follicular phase, but this analysis lacked power for multiple testing.

CONCLUSIONS:

Estrogen concentrations varied from cycle to cycle, and higher estrogen was associated with achieving clinical pregnancy.