BackgroundEvidence suggests that the hormonal milieu of pregnancy is an important determinant of subsequent cancer and other chronic diseases in both the mother and the offspring. Many of the existing maternity and birth cohorts include specimens drawn only once during pregnancy. How well a single blood specimen collected during a pregnancy characterizes exposure to these hormones throughout gestation, and also in subsequent pregnancies, is not well understood.MethodsWe used serial serum samples from 71 pregnant women (25 primiparous, 25 multiparous, and 21 with two consecutive pregnancies) with natural, complication-free pregnancies and a healthy offspring at term who participated in a population-based screening trial for congenital infections in Finland between January 1st, 1988 and June 30, 1989 and provided a blood sample in each trimester.ResultsHormone levels were more strongly correlated between consecutive trimesters of a pregnancy than between the 1st and 3rd trimester (e.g., estradiol, rT1 vs. T2 = 0.51 and rT2 vs. T3 = 0.60, p < 0.01; rT1 vs. T3 = 0.32, p < 0.05). Concentrations of sRANKL remained stable throughout gestation, whereas estradiol, estrone, progesterone, testosterone, prolactin, and osteoprotegerin increased throughout pregnancy. First trimester hormone concentrations explained less of the variation in the third trimester on their own than second trimester hormone levels (e.g. estradiol R2T1  = 16 % and R2T2 = 42 %). Addition of maternal (e.g., smoking) and/or child characteristics (e.g., sex) improved the accuracy of the 3rd trimester estimates for some of the hormones.ConclusionsOne hormone measurement in early pregnancy, in conjunction with maternal and fetal characteristics, permits estimation of 3rd trimester hormone concentrations. Therefore, single hormone measurements available from maternity cohorts are suitable to quantify hormone exposure during pregnancy. To our knowledge, we provide the first data on correlations between hormone concentrations both across trimesters of a single pregnancy, as well as between two subsequent pregnancies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12884-016-0937-5) contains supplementary material, which is available to authorized users.

Objective To examine the associations of maternal and child characteristics with early pregnancy maternal concentrations of testosterone, androstenedione, progesterone, 17-hydroxyprogesterone and estradiol. Methods We analyzed these hormones among 1,343 women with singleton pregnancies who donated serum samples to the Finnish Maternity Cohort from 1986 to 2006 during the first half of pregnancy (median, 11 weeks). The associations of maternal and child characteristics with hormone concentrations were investigated by correlation and multivariable regression. Results Women above age 30 had lower androgen and estradiol but higher progesterone concentrations than women below that age. Multiparous women had 14% lower testosterone, 11% lower androstenedione and 17-hydroxyprogesterone, 9% lower progesterone, and 16% lower estradiol concentrations compared to nulliparous women (all P<.05). Smoking mothers had 11%, 18%, and 8% higher testosterone, androstenedione, and 17-hydroxyprogesterone levels, respectively, but 10% lower progesterone compared to non-smoking women (all P<.05). Estradiol concentrations were 9% higher (P<0.05) among women with a female fetus compared to those with a male fetus. Conclusions Parity, smoking, and to a lesser extent maternal age and child gender are associated with sex steroid levels during the first half of a singleton pregnancy. The effects of smoking on the maternal hormonal environment and the possible long-term deleterious consequences on the fetus deserve further evaluation.