Vitamin D and Reproductive Hormones Across the Menstrual Cycle

STUDY QUESTION

How do the calciotropic hormones (25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and intact parathyroid hormone (iPTH)) vary across the menstrual cycle and do cyclic patterns of reproductive hormones (estradiol, progesterone, LH, FSH) differ by vitamin D status?

SUMMARY ANSWER

Calciotropic hormones vary minimally across the menstrual cycle; however, women with 25-hydroxyvitamin D below 30 ng/ml have lower mean estradiol across the menstrual cycle.

WHAT IS KNOWN ALREADY

Prior human studies suggest that vitamin D status is associated with fecundability, but the mechanism is unknown. Exogenous estrogens and prolonged changes in endogenous estradiol (pregnancy or menopause) influence concentrations of 25-hydroxyvitamin D. In vitro, treatment with 1,25-dihydroxyvitamin D increases steroidogenesis in ovarian granulosa cells. There are little data about changes in calciotropic hormones across the menstrual cycle or cyclic patterns of reproductive hormones by categories of vitamin D status.

STUDY DESIGN, SIZE, DURATION

A prospective cohort study of 89 self-identified white women aged 18-44, across two menstrual cycles. Participants were a subset of the BioCycle Study, a community-based study conducted at the University of Buffalo, 2005-2007.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Eligible participants had self-reported regular menstrual cycles between 21 and 35 days and were not using hormonal contraception or vitamins. Early morning fasting blood samples were drawn at up to eight study visits per cycle. Visits were timed to capture information in all cycle phases. Serum samples for 89 women (N = 163 menstrual cycles) were analyzed for estradiol, progesterone, LH, FSH and 25-hydroxyvitamin D (25(OH)D). Variability in calciotropic hormones within and across menstrual cycles was assessed using intraclass correlation coefficients and non-linear mixed models. Given the relative stability of the calciotropic hormones across the menstrual cycle, non-linear mixed models were used to examine differences in the cyclic patterns of estradiol, progesterone, LH and FSH by categories of each calciotropic hormone (split at the median). These models were conducted for all ovulatory cycles (N = 142 ovulatory menstrual cycles) and were adjusted for age, BMI (measured in clinic) and self-reported physical activity.

MAIN RESULTS AND THE ROLE OF CHANCE

Median 25(OH)D concentration was 29.5 ng/ml (SD 8.4), and only 6% of women had vitamin D deficiency (<20 ng/ml). The mean concentration of 25(OH)D did not differ between the luteal and follicular phase; however, both 1,25(OH)2D and iPTH showed small fluctuations across the menstrual cycle with the highest 1,25(OH)2D (and lowest iPTH) in the luteal phase. Compared with women who had mean 25(OH)D ≥30 ng/ml, women with lower 25(OH)D had 13.8% lower mean estradiol (95% confidence interval: -22.0, -4.7) and 10.8% lower free estradiol (95% CI: -0.07, -0.004). Additionally, compared to women with iPTH ≤36 pg/ml, women with higher concentrations of iPTH had 12.7% lower mean estradiol (95% CI: -18.7, -6.3) and 7.3% lower progesterone (95% CI: -13.3, -0.9). No differences in the cyclic pattern of any of the reproductive hormones were observed comparing cycles with higher and lower 1,25(OH)2D.

LIMITATIONS, REASONS FOR CAUTION

Women included in this study had self-reported 'regular' menstrual cycles and very few were found to have 25(OH)D deficiency. This limits our ability to examine cycle characteristics, anovulation and the effects of concentrations of the calciotropic hormones found in deficient individuals. Additionally, the results may not be generalizable to women with irregular cycles, other races, or populations with a higher prevalence of vitamin D deficiency.

WIDER IMPLICATIONS OF THE FINDINGS

These findings support current clinical practice that does not time testing for vitamin D deficiency to the menstrual cycle phase. We find that women with lower vitamin D status (lower 25(OH)D or higher iPTH) have lower mean concentrations of estradiol across the menstrual cycle. Although this study cannot identify a mechanism of action, further in vitro work or clinical trials may help elucidate the biologic mechanisms linking calciotropic and reproductive hormones.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Intramural Research Programs of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health (contract numbers: HHSN275200403394C, HHSN275201100002I and Task 1 HHSN27500001) and the National Institute of Environmental Health Sciences. There are no competing interests.

Pre-conception 25-hydroxyvitamin D (25(OH)D) and fecundability

STUDY QUESTION

Is pre-conception 25(OH)D associated with the per cycle probability of conception, i.e fecundability, in a prospective cohort study?

SUMMARY ANSWER

There are suggestive associations of high 25(OH)D (at least 50 ng/ml) with increased fecundability and low 25(OH)D (<20 ng/ml) with reduced fecundability, but the estimates were imprecise.

WHAT IS KNOWN ALREADY

Vitamin D has been associated with reproductive function and fertility in animal studies, but few human studies exist.

STUDY DESIGN, SIZE, DURATION

This community-based prospective cohort study included 522 women attempting to become pregnant between 2010 and 2016. The women completed online daily and monthly diaries until a positive home pregnancy test was observed or 12 months had elapsed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study included women from central North Carolina who were aged 30-44 with no history of infertility, with no more than 3 months of attempt time at recruitment. Women recorded vaginal bleeding so that the ongoing number of attempt cycles could be counted and used to quantify a woman's pregnancy attempt time. Blood collected at the study entry was analysed for 25(OH)D using liquid chromatography tandem mass spectrometry. Associations with fecundability were estimated with a log-binomial discrete time-to-event model.

MAIN RESULTS AND THE ROLE OF CHANCE

Among 522 women, 257 conceived during the study. The mean age was 33 years and the mean 25(OH)D was 36 ng/ml. There was an estimated 10% higher fecundability with each 10 ng/ml increase in 25(OH)D (fecundability ratio (FR) 1.10, 95% CI: 0.96, 1.25). The suggestive dose-response association with the continuous measure of 25(OH)D was driven by women in the lowest and the highest categories of 25(OH)D. Compared to women with 25(OH)D of 30-40 ng/ml, women below 20 ng/ml had an estimated 45% reduction in fecundability (FR (CI): 0.55 (0.23, 1.32)), and women with at least 50 ng/ml had an estimated 35% increase in fecundability (FR (CI): 1.35 (0.95, 1.91)). Across these three categories (25(OH)D of <20 ng/ml, 30-40 ng/ml and > 50 ng/ml), the probability of taking longer than 6 months to conceive was, respectively, 51% (17%, 74%), 28% (17%, 39%) and 15% (10%, 37%).

LIMITATIONS, REASONS FOR CAUTION

While the distribution of 25(OH)D was wide, the number of observed cycles with high 25(OH)D (N = 107) or low 25(OH)D (N = 56) was small.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings are consistent with prior reports of reduced fertility in women with 25(OH)D concentrations below the clinically defined deficiency level (20 ng/ml). Further studies are needed to evaluate the possible reproductive benefits of considerably higher 25(OH)D concentration (>50 ng/ml).

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health (NIH) under award numbers R00HD079659 and R01HD067683 and supported in part by the Intramural Research Program of the National Institute of Environmental Health Sciences, under projects ES103086, ES049003 and ES044003. ClearBlue ovulation predictor kits were generously donated to AMZJ and AJW by Swiss Precision Diagnostics. Drs Wilcox and Jukic report non-financial support from Swiss Precision Diagnostics during the conduct of the study; Dr Jukic reports non-financial support from Theralogix, LLC, outside the submitted work. Otherwise there are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

A single baseline ultrasound assessment of fibroid presence and size is strongly predictive of future uterine procedure: 8-year follow-up of randomly sampled premenopausal women aged 35-49 years

STUDY QUESTION

How well can a single baseline ultrasound assessment of fibroid burden (presence or absence of fibroids and size of largest, if present) predict future probability of having a major uterine procedure?

SUMMARY ANSWER

During an 8-year follow-up period, the risk of having a major uterine procedure was 2% for those without fibroids and increased with fibroid size for those with fibroids, reaching 47% for those with fibroids ≥ 4 cm in diameter at baseline.

WHAT IS KNOWN ALREADY

Uterine fibroids are a leading indication for hysterectomy. However, when fibroids are found, there are few available data to help clinicians advise patients about disease progression.

STUDY DESIGN, SIZE, DURATION

Women who were 35-49 years old were randomly selected from the membership of a large urban health plan; 80% of those determined to be eligible were enrolled and screened with ultrasound for fibroids ≥ 0.5 cm in diameter. African-American and white premenopausal participants who responded to at least one follow-up interview (N = 964, 85% of those eligible) constituted the study cohort. During follow-up (5822 person-years), participants self-reported any major uterine procedure (67% hysterectomies). Life-table analyses and Cox regression (with censoring for menopause) were used to estimate the risk of having a uterine procedure for women with no fibroids, small (<2 cm in diameter), medium (2-3.9 cm), and large fibroids (≥ 4 cm). Differences between African-American and white women, importance of a clinical diagnosis of fibroids prior to study enrollment, and the impact of submucosal fibroids on risk were investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

There was a greater loss to follow-up for African-Americans than whites (19 versus 11%). For those with follow-up data, 64% had fibroids at baseline, 33% of whom had had a prior diagnosis. Of those with fibroids, 27% had small fibroids (<2 cm in diameter), 46% had medium (largest fibroid 2-3.9 cm in diameter), and 27% had large fibroids (largest ≥ 4 cm in diameter). Twenty-one percent had at least one submucosal fibroid.

MAIN RESULTS AND THE ROLE OF CHANCE

Major uterine procedures were reported by 115 women during follow-up. The estimated risk of having a procedure in any given year of follow-up for those with fibroids compared with those without fibroids increased markedly with fibroid-size category (from 4-fold, confidence interval (CI) (1.4-11.1) for the small fibroids to 10-fold, CI (4.4-24.8) for the medium fibroids, to 27-fold, CI (11.5-65.2) for the large fibroids). This influence of fibroid size on risk did not differ between African-Americans and whites (P-value for interaction = 0.88). Once fibroid size at enrollment was accounted for, having a prior diagnosis at the time of ultrasound screening was not predictive of having a procedure. Exclusion of women with a submucosal fibroid had little influence on the results. The 8-year risk of a procedure based on lifetable analyses was 2% for women with no fibroids, 8, 23, and 47%, respectively, for women who had small, medium or large fibroids at enrollment. Given the strong association of fibroid size with subsequent risk of a procedure, these findings are unlikely to be due to chance.

LIMITATIONS, REASONS FOR CAUTION

Despite a large sample size, the number of women having procedures during follow-up was relatively small. Thus, covariates such as BMI, which were not important in our analyses, may have associations that were too small to detect with our sample size. Another limitation is that the medical procedures were self-reported. However, we attempted to retrieve medical records when participants agreed, and 77% of the total procedures reported were verified. Our findings are likely to be generalizable to other African-American and white premenopausal women in their late 30s and 40s, but other ethnic groups have not been studied.

WIDER IMPLICATIONS OF THE FINDINGS

Though further studies are needed to confirm and extend the results, our findings provide an initial estimate of disease progression that will be helpful to clinicians and their patients.

Use of depot medroxyprogesterone acetate and prevalent leiomyoma in young African American women

STUDY QUESTION

Is use of depot medroxyprogesterone acetate (DMPA) a risk factor for or a protective factor against prevalent uterine leiomyoma?

SUMMARY ANSWER

Ever use of DMPA was associated with a decreased risk (adjusted risk ratio (RR): 0.8, 95% confidence interval (CI): 0.6, 0.9) of prevalent leiomyoma in young African American women.

WHAT IS KNOWN ALREADY

Although progesterone is associated with growth of leiomyoma, previous epidemiological studies have shown a protective association for DMPA use. These previous studies may have been biased by studying clinically diagnosed leiomyoma (DMPA may mask symptoms thus delaying diagnoses).

STUDY DESIGN, SIZE, DURATION

Cross sectional analysis of baseline data from a cohort study of 1696 African American women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Community-based recruitment (e.g. letters, flyers, radio and TV announcements) were used to enroll African American women between 23 and 34 years old without a previous diagnosis of leiomyoma in the Metropolitan Detroit area. Extensive questionnaire data were used to determine DMPA use and screening ultrasound detected the presence of leiomyoma ≥0.5 cm in diameter. Relative risks with adjustment for covariates were calculated for the presence of leiomyoma based on ever use of DMPA as well as duration and recency of use.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the 1696 volunteers who enrolled, 43% had used DMPA. Leiomyoma were detected in 17% of those who had ever used DMPA compared with 26% of those who had never used DMPA. The reduction in prevalence remained after adjustment for potential confounders and was highest among women who had used DMPA for more than 4 years (adjusted RR: 0.5, 95% CI: 0.3, 0.8). The reduction in risk was seen for women whose most recent use was up to 8 years prior to study enrollment.

LIMITATIONS, REASONS FOR CAUTION

The use of cross-sectional data means that the timing of initial fibroid development is not known, so the temporality of the association is uncertain. However in this sample of young women, most fibroids were small, suggesting that DMPA exposure may have occurred before leiomyoma development.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings are in agreement with previous epidemiological studies, but protected from the bias inherent in the use of clinically diagnosed leiomyoma. Although further studies will be needed to elucidate the mechanism, use of DMPA as a contraceptive appears to provide long lasting protection against uterine leiomyoma.

STUDY FUNDING/COMPETING INTERESTS

No competing interests. This research was supported in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences, and in part by funds allocated for health research by the American Recovery and Reinvestment Act.

TRIAL REGISTRATION NUMBER

N/A.

Length of human pregnancy and contributors to its natural variation

STUDY QUESTION

How variable is the length of human pregnancy, and are early hormonal events related to gestational length?

SUMMARY ANSWER

Among natural conceptions where the date of conception (ovulation) is known, the variation in pregnancy length spanned 37 days, even after excluding women with complications or preterm births.

WHAT IS KNOWN ALREADY

Previous studies of length of gestation have either estimated gestational age by last menstrual period (LMP) or ultrasound (both imperfect measures) or included pregnancies conceived through assisted reproductive technology.

STUDY DESIGN, SIZE, DURATION

The Early Pregnancy Study was a prospective cohort study (1982-85) that followed 130 singleton pregnancies from unassisted conception to birth, with detailed hormonal measurements through the conception cycle; 125 of these pregnancies were included in this analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We calculated the length of gestation beginning at conception (ovulation) in 125 naturally conceived, singleton live births. Ovulation, implantation and corpus luteum (CL) rescue pattern were identified with urinary hormone measurements. We accounted for events that artificially shorten the natural length of gestation (Cesarean delivery or labor induction, i.e. 'censoring') using Kaplan-Meier curves and proportional hazards models. We examined hormonal and other factors in relation to length of gestation. We did not have ultrasound information to compare with our gold standard measure.

MAIN RESULTS AND THE ROLE OF CHANCE

The median time from ovulation to birth was 268 days (38 weeks, 2 days). Even after excluding six preterm births, the gestational length range was 37 days. The coefficient of variation was higher when measured by LMP (4.9%) than by ovulation (3.7%), reflecting the variability of time of ovulation. Conceptions that took longer to implant also took longer from implantation to delivery (P = 0.02). CL rescue pattern (reflecting ovarian response to implantation) was predictive (P = 0.006): pregnancies with a rapid progesterone rise were longer than those with delayed rise (a 12-day difference in the median gestational length). Mothers with longer gestations were older (P = 0.02), had longer pregnancies in other births (P < 0.0001) and were heavier at birth (P = 0.01). We did not see an association between the length of gestation and several factors that have been associated with gestational length in previous studies: body mass index, alcohol intake, parity or offspring sex.

LIMITATIONS, REASONS FOR CAUTION

The sample size was small and some exposures were rare, reducing power to detect weak associations.

WIDER IMPLICATIONS OF THE FINDINGS

Human gestational length varies considerably even when measured exactly (from ovulation). An individual woman's deliveries tend to occur at similar gestational ages. Events in the first 2 weeks after conception are predictive of subsequent pregnancy length, and may suggest pathways underlying the timing of delivery.

STUDY FUNDING/COMPETING INTEREST

This research was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences. None of the authors has any conflict of interest to declare.

Risk of miscarriage among black women and white women in a U.S. Prospective Cohort Study

Many adverse pregnancy outcomes differ by race. We examined the association between self-reported race and miscarriage (pregnancy loss at <20 weeks) in a community-based pregnancy cohort. Women from the southeastern United States (North Carolina, Texas, and Tennessee) were enrolled in "Right from the Start" from 2000 to 2009. They were recruited while trying to conceive or during early pregnancy. Participants completed study ultrasound examinations, interviews, and consent forms for review of medical records. We used proportional hazard models to examine miscarriage risk among black women compared with white women, adjusted for confounders. There were 537 observed miscarriages among 4,070 women, 23% of whom self-identified as black (n = 932). The life table-adjusted cumulative risk of loss after gestational week 5 was 21.3%. With adjustment for age and alcohol use, blacks had increased risk of miscarriage compared with whites (adjusted hazard ratio = 1.57, 95% confidence interval: 1.27, 1.93). When risk of loss before gestational week 10 was dichotomized at the median gestational age, there was little difference, but black women had a greater risk thereafter compared with white women (adjusted hazard ratio = 1.93, 95% confidence interval: 1.48, 2.51). Early pregnancy ultrasound examinations did not differ by race. In summary, self-reported race is independently associated with risk of miscarriage, and the higher risk for black women is concentrated in gestational weeks 10-20.

First-trimester bleeding characteristics associate with increased risk of preterm birth: data from a prospective pregnancy cohort

BACKGROUND

Prior evidence linking first-trimester bleeding with preterm birth (PTB, <37 weeks gestation) risk has been inconsistent and may be biased by subject selection and/or incomplete documentation of bleeding episodes for all participants. Prior studies have not carefully examined the role of bleeding characteristics in PTB risk. In the present study, we estimate the association between first-trimester bleeding and PTB in a non-clinical prospective cohort and test whether bleeding characteristics better predict risk.

METHODS

Women were enrolled in Right from the Start (2000-2009), a prospective pregnancy cohort. Data about bleeding and bleeding characteristics were examined with logistic regression to assess association with PTB.

RESULTS

Among 3978 pregnancies 344 were PTB and 3634 term. Bleeding was reported by 986 (26%) participants. After screening candidate confounders, only multiple gestations remained in the model. Bleeding associated with PTB [odds ratio (OR)(adjusted) = 1.40, 95% confidence interval (CI) 1.09-1.80]. Risk did not vary by race/ethnicity. Compared with non-bleeders, PTB risk was higher for bleeding with red color (OR(adjusted) = 1.92, 95% CI, 1.32-2.82), for heavy episodes (OR(adjusted) = 2.40, 95% CI 1.18-4.88) and long duration (OR(adjusted) = 1.67, 95% CI 1.17-2.38).

CONCLUSIONS

Bleeding associated with PTB was not confounded by common risk factors for bleeding or PTB. PTB risk was greatest for women with heavy bleeding episodes with long duration and red color and would suggest that combining women with different bleeding characteristics may affect the accuracy of risk assessment. These data suggest a candidate etiologic pathway for PTB and warrant further investigation of the biologic mechanisms.

Fecundability among women with type 1 and type 2 diabetes in the Norwegian Mother and Child Cohort Study

AIMS/HYPOTHESIS

We assessed the effects of type 1 diabetes and type 2 diabetes on fecundability (as manifest by increased time-to-pregnancy [TTP]) in a large cohort of pregnant women.

METHODS

This study is based on the Norwegian Mother and Child Cohort Study. Members of this large cohort were enrolled early in pregnancy and asked about TTP and other factors. Among the 58,004 women included in the analysis, we identified 221 cases of type 1 diabetes and 88 cases of type 2 diabetes using the Medical Birth Registry of Norway. A logistic analogue of the proportional probability model, a Cox-like discrete-time model, was used to compute fecundability odds ratios (FORs) and 95% CI for type 1 diabetes and type 2 diabetes, adjusted for maternal age and prepregnancy BMI.

RESULTS

Compared with non-diabetic women, the adjusted FOR for women with type 1 diabetes was 0.76 (95% CI 0.64-0.89) and the adjusted FOR for women with type 2 diabetes was 0.64 (95% CI 0.48-0.84). These FORs did not change substantively and remained statistically significant after excluding women with irregular menstrual cycles and accounting for cycle length.

CONCLUSIONS/INTERPRETATION

The results from the present study provide evidence of substantially decreased fecundability for women with type 1 and type 2 diabetes, even among those with a normal menstrual cycle.

The association of maternal factors with delayed implantation and the initial rise of urinary human chorionic gonadotrophin

BACKGROUND Late implantation and the pattern of early rise in hCG have been associated with early pregnancy loss. We explored factors that might be predictive of these markers of poor embryonic health in spontaneously conceived pregnancies. METHODS Participants in the North Carolina Early Pregnancy Study collected daily first-morning urine specimens while attempting to conceive. Samples were assayed for estrogen and progesterone metabolites (to identify day of ovulation) and hCG (to detect conception). Data were available for 190 pregnancies, 48 of which ended in early loss (within 6 weeks of the last menstrual period). We used logistic regression to identify characteristics associated with late implantation (≥10 days post-ovulation). For pregnancies surviving at least 6 weeks (n= 142), we used linear mixed models to identify factors associated with variations in hCG rise in the first 7 days from detection. RESULTS Later implantation was associated with current maternal smoking [odds ratio (OR): 5.7; 95% confidence interval (CI): 1.1-30] and with oocytes that were likely to have been fertilized late in their post-ovulatory lifespan (OR: 5.1; CI: 1.9-16). Older women had a faster rise in hCG (P= 0.01), as did women who had relatively late menarche (P for trend = 0.02). Women exposed in utero to diethylstilbestrol showed an unusual pattern of slow initial hCG rise followed by a fast increase, a pattern significantly different from that of unexposed women (P= 0.002). CONCLUSIONS Although limited by small numbers and infrequent exposures, our analyses suggest that a woman's exposures both early in life and at the time of pregnancy may influence early development of the conceptus.

In utero exposure to maternal smoking and women's risk of fetal loss in the Norwegian Mother and Child Cohort (MoBa)

BACKGROUND

Whether in utero exposure to tobacco smoke increases a woman's risk of fetal loss later in life is unknown, though data on childhood exposure suggest an association may exist. This study evaluated the association between in utero exposure to tobacco smoke and fetal loss in the Norwegian Mother and Child Cohort Study (MoBa), which enrolled ∼40% of the pregnant women in Norway from 1999 to 2008.

METHODS

Information on exposure to tobacco smoke in utero, the woman's own smoking behavior during pregnancy and other factors was obtained by a questionnaire completed at ∼17 weeks of gestation. Subsequent late miscarriage (fetal death <20 weeks) and stillbirth (fetal death ≥ 20 weeks) were ascertained from the Norwegian Medical Birth Registry. This analysis included 76 357 pregnancies (MoBa data set version 4.301) delivered by the end of 2008; 59 late miscarriages and 270 stillbirths occurred. Cox proportional hazards models were fit for each outcome and for all fetal deaths combined.

RESULTS

The adjusted hazard ratio (HR) of late miscarriage was 1.23 [95% confidence interval (CI), 0.72-2.12] in women with exposure to maternal tobacco smoke in utero when compared with non-exposed women. The corresponding adjusted HR for stillbirths was 1.11 (95% CI, 0.85-1.44) and for all fetal deaths combined, it was 1.12 (95% CI, 0.89-1.43).

CONCLUSIONS

The relatively wide CI around the HR for miscarriage reflected the limited power to detect an association, due to enrollment around 17 weeks of gestation. However, for in utero exposure to tobacco smoke and risk of stillbirth later in life, where the study power was adequate, our data provided little support for an association.

Urinary hCG patterns during the week following implantation

BACKGROUND

Human chorionic gonadotrophin (hCG) is used to monitor pregnancy status. Yet the pattern of hCG excretion in the first week following implantation has not been adequately described. Therefore the aim of this study was to describe the average profile of hCG and its variability during the 7 days following estimated implantation in a population of naturally conceived pregnancies.

METHODS

We measured daily hCG concentrations in first-morning urine for 142 clinical pregnancies from women with no known fertility problems. Mixed-effects regression models were used to estimate the hCG trajectory and its variability in relation to pregnancy outcomes.

RESULTS

hCG rose 3-fold between the day of detection and the next day (95% CI = 2.7-3.4). The relative rate of rise decreased thereafter, reaching 1.6-fold (95% CI = 1.5-1.8) between days 6 and 7. HCG levels followed a log-quadratic trajectory, and the patterns of rise were unrelated to number of fetuses, risk of spontaneous abortion or sex of the baby. Later implantations (after 10 luteal days) produced slower rates of increase.

CONCLUSIONS

Although mean hCG follows a log-quadratic trajectory during the first week of detectability, there is high variability across pregnancies. Later implantation may reflect characteristics of the uterus or conceptus that slow hCG production.

Bleeding following pregnancy loss before 6 weeks' gestation

BACKGROUND

Pregnancy loss before 6 weeks' gestation is common, but little has been reported about the associated bleeding. We compared women's bleeding following a pregnancy loss before 6 weeks' gestation with their typical menstruation.

METHODS

Women provided daily urine samples while trying to become pregnant and recorded the number of pads and tampons used each day. Thirty-six women had complete bleed data for a loss before 6 weeks' gestation and one or more non-pregnant cycles.

RESULTS

Mean bleed length following a pregnancy loss was 0.4 days longer than the woman's average menstrual bleed (P = 0.01), primarily because of more days of light bleeding. Although there was no overall increase in the total number of pads plus tampons used, women with losses bled less than their typical menses following pregnancies of very short duration and more than usual for the pregnancies lasting the longest.

CONCLUSIONS

Overall, the bleeding associated with pregnancy loss before 6 weeks' gestation is similar to menstrual bleeding and unlikely to be recognized as pregnancy loss. The intriguing finding that pregnancies of very short duration were associated with less bleeding than the woman's typical menses might reflect endometrial factors associated with loss.

Fertility and exposure to solvents among families in the Agricultural Health Study

BACKGROUND

Several studies have reported associations between solvent exposure and reduced female fertility, but the evidence is inconclusive for male fertility.

OBJECTIVES

To investigate the impact of solvent exposure on subfertility among families of male licensed pesticide applicators in the Agricultural Health Study cohort.

METHODS

The couples enrolled between 1993 and 1997. Cross-sectional questionnaire information on work tasks was used to assess exposure to solvents. The data were limited to couples (wife aged less than 40 years) with an attempt at pregnancy in the last four years (n = 2112).

RESULTS

Twenty eight per cent of the couples were defined as subfertile (not conceiving a pregnancy after at least 12 months of unprotected intercourse, regardless of whether or not a pregnancy ultimately occurred). Adjusted subfertility odds ratios (OR) for exposure to solvents were calculated with logistic regression. Female (OR 1.42, 95% CI 1.15 to 1.75) and male exposure to solvents (OR 1.21 (95% CI 0.93 to 1.57) for monthly exposure and 1.40 (95% CI 0.97 to 2.03) for daily or weekly exposure) were associated with subfertility. In farming, spouses may share or exchange jobs. To account for potential dual exposure, variables for parental exposure (either parent exposed or both parents exposed) were also defined. Both were strongly associated with subfertility (OR 1.62 (95% CI 1.20 to 2.17) and OR 2.10 (95% CI 1.22 to 3.60), respectively).

CONCLUSIONS

Solvents may impair fertility of either gender, though the evidence for female effects is stronger than for male effects.

Biomarkers of oxidative stress study III. Effects of the nonsteroidal anti-inflammatory agents indomethacin and meclofenamic acid on measurements of oxidative products of lipids in CCl4 poisoning

Plasma and urinary levels of malondialdehyde-like products (MDA) and isoprostanes were identified as markers of in vivo lipid peroxidation in an animal model of CCl4 poisoning. We sought to determine the extent to which the formation of these oxidation products is influenced by inhibition of the cyclooxygenase enzymes which catalytically generate proinflammatory lipid peroxidation products known as prostaglandins and thromboxane. In the present studies, after induction of oxidant stress in rats with CCl4, lipid peroxidation products measured in plasma and urine demonstrate that isoprostanes and MDA can be partially inhibited by cyclooxygenase inhibitors, albeit to different extents. The lowering of isoprostane and MDA formation, however, may not to due primarily to the diminution of catalytic generation of isoprostanes or MDA by the cyclooxygenases but, rather, may be the result of the suppression of nonenzymatic lipid peroxidation. This is suggested since 8,12-iso-iPF2alpha-VI is also reduced by indomethacin, yet, unlike other isoprostanes and MDA, it is not generated catalytically by the cyclooxygenase. Thus, although the two cyclooxygenase inhibitors we tested have statistically significant effects on the measurements of both isoprostanes and MDA in this study, the results provide evidence that these lipid-degradation products primarily constitute markers of oxidative stress.

Biomarkers of oxidative stress study II: are oxidation products of lipids, proteins, and DNA markers of CCl4 poisoning?

Oxidation products of lipids, proteins, and DNA in the blood, plasma, and urine of rats were measured as part of a comprehensive, multilaboratory validation study searching for noninvasive biomarkers of oxidative stress. This article is the second report of the nationwide Biomarkers of Oxidative Stress Study using acute CCl4 poisoning as a rodent model for oxidative stress. The time-dependent (2, 7, and 16 h) and dose-dependent (120 and 1200 mg/kg i.p.) effects of CCl4 on concentrations of lipid hydroperoxides, TBARS, malondialdehyde (MDA), isoprostanes, protein carbonyls, methionine sulfoxidation, tyrosine products, 8-hydroxy-2'-deoxyguanosine (8-OHdG), leukocyte DNA-MDA adducts, and DNA-strand breaks were investigated to determine whether the oxidative effects of CCl4 would result in increased generation of these oxidation products. Plasma concentrations of MDA and isoprostanes (both measured by GC-MS) and urinary concentrations of isoprostanes (measured with an immunoassay or LC/MS/MS) were increased in both low-dose and high-dose CCl4-treated rats at more than one time point. The other urinary markers (MDA and 8-OHdG) showed significant elevations with treatment under three of the four conditions tested. It is concluded that measurements of MDA and isoprostanes in plasma and urine as well as 8-OHdG in urine are potential candidates for general biomarkers of oxidative stress. All other products were not changed by CCl4 or showed fewer significant effects.

Vaginal bleeding in very early pregnancy

INTRODUCTION

Little is known about the occurrence and patterns of vaginal bleeding during the earliest stages of pregnancy. We explore this in a prospective study of early pregnancy.

METHODS

A total of 221 healthy women kept daily diaries and provided daily urine samples while trying to become pregnant. Of these, 151 women became clinically pregnant [i.e. pregnancy that lasted >/=6 weeks beyond last menstrual period (LMP)] during the study. Diaries provided information on days with vaginal bleeding and sexual intercourse. Urine hormone assays were used to identify ovulation and implantation. Women were interviewed about their medical histories and lifestyle factors.

RESULTS

A total of 14 women (9%) recorded at least 1 day of vaginal bleeding during the first 8 weeks of pregnancy. Twelve of these 14 pregnancies continued to a live birth. Bleeding tended to occur around the time when women would expect their periods, although rarely on the day of implantation. Bleeding was not associated with intercourse.

CONCLUSIONS

Early bleeding in clinical pregnancies is generally light, and not likely to be mistaken for LMP. Thus, early bleeding is unlikely to contribute to errors in LMP-based gestational age. We found no support for the hypothesis that implantation can produce vaginal bleeding. Similarly, intercourse did not cause bleeding. Nearly all women with bleeding went on to have successful pregnancies.

Natural limits of pregnancy testing in relation to the expected menstrual period

CONTEXT

Pregnancy test kits routinely recommend testing "as early as the first day of the missed period." However, a pregnancy cannot be detected before the blastocyst implants. Due to natural variability in the timing of ovulation, implantation does not necessarily occur before the expected onset of next menses.

OBJECTIVE

To estimate the maximum screening sensitivity of pregnancy tests when used on the first day of the expected period, taking into account the natural variability of ovulation and implantation.

DESIGN AND SETTING

Community-based prospective cohort study conducted in North Carolina between 1982 and 1986.

PARTICIPANTS

Two hundred twenty-one healthy women 21 to 42 years of age who were planning to conceive.

MAIN OUTCOME MEASURES

Day of implantation, defined by the serial assay of first morning urine samples using an extremely sensitive immunoradiometric assay for human chorionic gonadotropin (hCG), relative to the first day of the missed period, defined as the day on which women expected their next menses to begin, based on self-reported usual cycle length.

RESULTS

Data were available for 136 clinical pregnancies conceived during the study, 14 (10%) of which had not yet implanted by the first day of the missed period. The highest possible screening sensitivity for an hCG-based pregnancy test therefore is estimated to be 90% (95% confidence interval [CI], 84%-94%) on the first day of the missed period. By 1 week after the first day of the missed period, the highest possible screening sensitivity is estimated to be 97% (95% CI, 94%-99%).

CONCLUSIONS

In this study, using an extremely sensitive assay for hCG, 10% of clinical pregnancies were undetectable on the first day of missed menses. In practice, an even larger percentage of clinical pregnancies may be undetected by current test kits on this day, given their reported assay properties and other practical limitations.

No evidence for lipid peroxidation in severe preeclampsia

OBJECTIVE

This study was undertaken to address the role of oxidative stress in preeclampsia.

STUDY DESIGN

We measured urinary 8,12-iso-iPF(2alpha)-VI, a chemically stable, free-radical catalyzed product, in a case control study of severe preeclampsia nested within the trial of Calcium for Preeclampsia Prevention. Cases included 29 women who developed severe preeclampsia and from whom urine had been obtained 10 to 20 weeks before the diagnosis of preeclampsia, 3 to 9 weeks before, and 1 day before through delivery. Controls did not develop hypertension or proteinuria and were matched to cases by center, gestational age at each of 3 corresponding urine collections, and date of enrollment.

RESULTS

Urinary 8,12-iso -iPF(2alpha)-VI did not differ significantly between cases and controls before or at diagnosis of preeclampsia, nor did it vary with gestational age.

CONCLUSIONS

These results call into question the importance of oxidative stress in the disease and the biochemical rationale for clinical trials of antioxidants to prevent and treat preeclampsia.

Measures of menopausal status in relation to demographic, reproductive, and behavioral characteristics in a population-based study of women aged 35-49 years

The purpose of this cross-sectional analysis of women aged 35-49 years from the Third National Health and Nutrition Examination Survey, conducted between 1988 and 1994, was to assess associations with menopausal status based either on menstrual cycle patterns or on elevated (>20 IU/liter) follicle-stimulating hormone. Menstrual cycle-based menopausal status was defined for women who had not had surgical menopause by months since the last period (<2, 2-12, and >12 months for pre-, peri-, and postmenopause, respectively). Logistic regression was adjusted for age, smoking, and unilateral oophorectomy. Higher body mass index (> or =30 kg/m(2) compared with < 25.0 kg/m(2)) was associated with a lower likelihood of elevated follicle-stimulating hormone (odds ratio (OR)=0.6, 95% confidence interval (CI): 0.4, 0.9) but this association was not seen with the menstrual measure of menopause. Exercise (three or more times per week) was associated with a lower likelihood of being postmenopausal on the basis of menstrual (OR = 0.3, 95% CI: 0.2, 0.7) and hormonal (OR = 0.6, 95% CI: 0.4, 1.0) measures. Alcohol use also tended to be associated with postmenopausal status by either measure, but not significantly so. There was little evidence of associations with ethnicity, education, age at menarche, number of livebirths, and oral contraceptive use. Menstrual-based definitions of menopause can be misclassified for women with menstrual irregularity. This might explain why obese women were classified menstrually as menopausal while remaining hormonally premenopausal.

A flexible parametric model for combining current status and age at first diagnosis data

In some cross-sectional studies of chronic disease, data consist of the age at examination, whether the disease was present at the exam, and recall of the age at first diagnosis. This article describes a flexible parametric approach for combining current status and age at first diagnosis data. We assume that the log odds of onset by a given age and of detection by a given age conditional on onset by that age are nondecreasing functions of time plus linear combinations of covariates. Piecewise linear models are used to characterize changes across time in the baseline odds. Methods are described for accommodating informatively missing current status data and inferences based on the age-specific incidence of disease prior to a landmark event (e.g., puberty, menopause). Our formulation enables straightforward maximum likelihood estimation without requiring restrictive parametric or Markov assumptions. The methods are applied to data from a study of uterine fibroids.

Likelihood of conception with a single act of intercourse: providing benchmark rates for assessment of post-coital contraceptives

Emergency post-coital contraceptives effectively reduce the risk of pregnancy, but their degree of efficacy remains uncertain. Measurement of efficacy depends on the pregnancy rate without treatment, which cannot be measured directly. We provide indirect estimates of such pregnancy rates, using data from a prospective study of 221 women who were attempting to conceive. We previously estimated the probability of pregnancy with an act of intercourse relative to ovulation. In this article, we extend these data to estimate the probability of pregnancy relative to intercourse on a given cycle day (counting from onset of previous menses). In assessing the efficacy of post-coital contraceptives, other approaches have not incorporated accurate information on the variability of ovulation. We find that the possibility of late ovulation produces a persistent risk of pregnancy even into the sixth week of the cycle. Post-coital contraceptives may be indicated even when intercourse has occurred late in the cycle.

Assessing human fertility using several markers of ovulation

In modelling human fertility one ideally accounts for timing of intercourse relative to ovulation. Measurement error in identifying the day of ovulation can bias estimates of fecundability parameters and attenuate estimates of covariate effects. In the absence of a single perfect marker of ovulation, several error prone markers are sometimes obtained. In this paper we propose a semi-parametric mixture model that uses multiple independent markers of ovulation to account for measurement error. The model assigns each method of assessing ovulation a distinct non-parametric error distribution, and corrects bias in estimates of day-specific fecundability. We use a Monte Carlo EM algorithm for joint estimation of (i) the error distribution for the markers, (ii) the error-corrected fertility parameters, and (iii) the couple-specific random effects. We apply the methods to data from a North Carolina fertility study to assess the magnitude of error in measures of ovulation based on urinary luteinizing hormone and metabolites of ovarian hormones, and estimate the corrected day-specific probabilities of clinical pregnancy. Published in 2001 by John Wiley & Sons, Ltd.

Development and reliability of a Telephone-Administered Perceived Racism Scale (TPRS): a tool for epidemiological use

The conceptualization of perceived racism as a chronic stressor is relatively new to epidemiology. The Telephone-Administered Perceived Racism Scale (TPRS) captures the complexity of racism within five scales: Experience of Racism (by Blacks as a group and by the respondent), Emotional Responses, Behavioral Responses, Concern for Child(ren), and Past Experiences of Racism. The TPRS was developed for employed Black women. Exploratory factor analyses and tests of internal consistency were completed with 476 Black women, aged 36-53. Factor analyses on their responses to racism yielded five factors: passive emotions, active emotions, passive behaviors, internal active behaviors, and external active behaviors. Alpha reliability values ranged from 0.75 to 0.80 for the active and passive emotions subscales, from 0.59 to 0.69 for the passive behaviors subscale, and greater than 0.76 for both active behaviors subscales. Alpha reliabilities were 0.82, 0.90, 0.88, and 0.82 for Past Experiences, Concern for Child(ren), Experience of Racism--Personal, and Experience of Racism--Group, respectively. Another 30 Black women were queried for test-retest reliability, with values ranging from 0.61 to 0.82. The TPRS was found to be reliable and should serve as a useful epidemiological tool in the examination of the effects of perceived racism on Black women's health.

The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study

OBJECTIVES

To provide specific estimates of the likely occurrence of the six fertile days (the "fertile window") during the menstrual cycle.

DESIGN

Prospective cohort study.

PARTICIPANTS

221 healthy women who were planning a pregnancy.

MAIN OUTCOME MEASURES

The timing of ovulation in 696 menstrual cycles, estimated using urinary metabolites of oestrogen and progesterone.

RESULTS

The fertile window occurred during a broad range of days in the menstrual cycle. On every day between days 6 and 21, women had at minimum a 10% probability of being in their fertile window. Women cannot predict a sporadic late ovulation; 4-6% of women whose cycles had not yet resumed were potentially fertile in the fifth week of their cycle.

CONCLUSIONS

In only about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines-that is, between days 10 and 17. Most women reach their fertile window earlier and others much later. Women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.

Epidemiologic contributions to understanding the etiology of uterine leiomyomata

Uterine leiomyomata are hormonally dependent tumors that are a major source of gynecologic morbidity among women of reproductive age. Relatively few studies have attempted to identify specific risk factors for these neoplasms. In this review of epidemiologic contributions to the etiology of uterine leiomyomata, we begin by outlining methodologic issues in epidemiologic studies that arise from the fact that a large proportion of uterine leiomyomata does not come to medical attention. We then review the major findings from published epidemiologic studies, which to date have focused primarily on menstrual and childbearing history, exogenous hormone use, obesity, cigarette smoking, and other lifestyle and behavioral characteristics that may in part reflect aspects of a woman's hormonal milieu. None of the potential risk factors studied have demonstrated sufficiently consistent associations to guide decisions on the primary prevention of uterine leiomyomata. Clarifying the etiology and natural history of uterine leiomyomata will require studies designed to address methodologic issues and test hypotheses involving environmental and lifestyle influences on endocrine function, as well as on other possible etiologic mechanisms. Recent advances in molecular genetics present opportunities for epidemiologic studies of uterine leiomyomata to incorporate biomarkers of somatic changes found in these tumors and to examine inherited genetic factors related to possible causal physiologic mechanisms.

Biomarkers of oxidative stress study: are plasma antioxidants markers of CCl(4) poisoning?

Antioxidants in the blood plasma of rats were measured as part of a comprehensive, multilaboratory validation study searching for noninvasive biomarkers of oxidative stress. For this initial study an animal model of CCl(4) poisoning was studied. The time (2, 7, and 16 h) and dose (120 and 1200 mg/kg, intraperitoneally)-dependent effects of CCl(4) on plasma levels of alpha-tocopherol, coenzyme Q (CoQ), ascorbic acid, glutathione (GSH and GSSG), uric acid, and total antioxidant capacity were investigated to determine whether the oxidative effects of CCl(4) would result in losses of antioxidants from plasma. Concentrations of alpha-tocopherol and CoQ were decreased in CCl(4)-treated rats. Because of concomitant decreases in cholesterol and triglycerides, it was impossible to dissociate oxidation of alpha-tocopherol and the loss of CoQ from generalized lipid changes, due to liver damage. Ascorbic acid levels were higher with treatment at the earliest time point; the ratio of GSH to GSSG generally declined, and uric acid remained unchanged. Total antioxidant capacity showed no significant change except for 16 h after the high dose, when it was increased. These results suggest that plasma changes caused by liver malfunction and rupture of liver cells together with a decrease in plasma lipids do not permit an unambiguous interpretation of the results and impede detection of any potential changes in the antioxidant status of the plasma.

Age at menopause and childbearing patterns in relation to mortality

Several studies have reported increased mortality risk with early natural menopause. More recently, mortality risk was reported to be reduced among women who gave birth at age > or =40 years. The association between reproductive history and mortality was explored among 826 women in a prospective study involving 18,959 person-years of follow-up (from age 50 to 1990-1991) and 108 deaths. After adjustment for age and other covariates, the risk ratio among parous women was 1.53 (95% confidence interval: 0.58, 4.07) for natural menopause at age < or =45 years compared with > or =51 years. In contrast to a previous report, however, the highest estimated mortality risk was seen among women who gave birth in their forties (adjusted risk ratio = 2.14, 95% confidence interval: 1.05, 4.38) compared with having a last birth at ages 30-34 years.

The associations of adolescent cigarette smoking, alcoholic beverage consumption, environmental tobacco smoke, and ionizing radiation with subsequent breast cancer risk (United States)

OBJECTIVES

Studies of breast cancer among survivors of the World War II atomic bomb blasts over Japan suggest that the adolescent breast may be particularly sensitive to carcinogenic insult. To further explore that possibility we examined the relationships of cigarette smoking, alcohol consumption, environmental tobacco smoke (ETS) exposure, and medical treatment with ionizing radiation during adolescence with subsequent breast cancer risk.

METHODS

Data from the Carolina Breast Cancer Study, a population-based, case-control study of breast cancer in North Carolina women aged 20-74 years (864 cases, 790 controls), were analyzed.

RESULTS

A modest increase in breast cancer risk was suggested for women who began to smoke cigarettes between the ages of 10 and 14 years (OR: 1.5, CI: 0.9-2.5), and for women exposed to ionizing radiation between ages 10 and 19 years to treat or monitor a medical condition (OR: 1.6, CI: 0.5-2.5). Neither exposure to ETS at home prior to age 18 years (OR: 1.1, CI: 0.9-1.3) nor initiation of alcoholic beverage consumption between ages 10 and 15 years (OR: 1.1, CI: 0.6-1.8) appeared to increase risk.

CONCLUSIONS

Our results are consistent with previous evidence suggesting that some adolescent exposures could influence future breast cancer risk.

Urinary oestrogen patterns in long follicular phases

Long menstrual cycles have been associated with reduced risk of breast cancer and increased risk of osteoporosis. These observations have led to assumptions about the endogenous oestrogen exposure of women with long cycles. However, daily oestrogen profiles in long menstrual cycles have not been described. This paper examines daily urinary oestrogen profiles during the follicular phases of 416 conception and non-conception cycles. Women were aged 21-42 years, had no history of infertility and were not under treatment. Twenty-eight cycles were defined as long, with a follicular phase that lasted 24 days or more. Five patterns were observed among these long cycles, the most common being a pattern consistent with delayed emergence of a dominant follicle. Other patterns were a pattern consistent with demise and replacement of a dominant follicle, one consistent with delayed follicular recruitment, one showing a prolonged initial drop in oestrogen and one with an extended oestrogen peak. Average follicular phase oestrogen concentrations were highest in cycles with short follicular phases (7-11 days). Oestrogen concentrations from long follicular phases (24-59 days) did not differ substantially from follicular phases of usual length (12-17 days). The oestrogen profiles in long follicular phases are heterogeneous and not necessarily hypo-oestrogenic.

Physical activity at age 12 and adult breast cancer risk (United States)

OBJECTIVES

Some epidemiologic studies suggest that adolescent physical activity reduces subsequent breast cancer risk. To examine this question further, we analyzed data on physical activity at age 12 that had been collected as part of the Carolina Breast Cancer Study (CBCS).

METHODS

The CBCS is a population-based, case-control study of 527 white and 337 African-American cases and 790 controls, frequency-matched on age and race. Respondents were asked whether, and to what extent, they engaged in four specific activities at age 12 (walking to school, biking to school, competitive training, performing vigorous household chores).

RESULTS

Women who reported participation in any of the four activities had a modest reduction in breast cancer risk (odds ratio (OR): 0.8, 95% confidence interval (CI): 0.6-1.0). Using an index measuring approximate number of activity episodes per week, analyses revealed modest inverse relationships for nearly all levels of activity relative to no reported activity; a weighting of the index by metabolic equivalent scores produced similar results.

CONCLUSIONS

Our findings support the hypothesis that adolescent physical activity may protect against adult breast cancer, even at moderate levels.

Adolescent reproductive events and subsequent breast cancer risk

OBJECTIVES

This study investigated the relationship between reproductive events during adolescence and subsequent breast cancer risk.

METHODS

Logistic regression models used self-reported data from 862 case patients and 790 controls in the Carolina Breast Cancer Study.

RESULTS

Miscarriage, induced abortion, and full-term pregnancy before 20 years of age were not associated with breast cancer. Among premenopausal women, breast-feeding before 20 years of age was inversely associated with disease. Oral contraceptive use before 18 years of age was positively associated with disease risk among African American women only.

CONCLUSIONS

Pregnancy during adolescence does not appear to influence breast cancer risk, but breast-feeding may. A possible increased breast cancer risk among African American women who used oral contraceptives as adolescents warrants further study.

Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation

Two studies have related the timing of sexual intercourse (relative to ovulation) to day-specific fecundability. The first was a study of Catholic couples practising natural family planning in London in the 1950s and 1960s and the second was of North Carolina couples attempting to become pregnant in the early 1980s. The former identified ovulation based on the ovulatory shift in the basal body temperature, while the latter used urinary assays of hormones. We use a statistical model to correct for error in identifying ovulation and to re-estimate the length of the fertile window and day-specific fecundabilities. We estimate the same 6-day fertile interval in both studies after controlling for error. After adjusting for error both data sets showed the highest estimate of the probability of pregnancy on the day prior to ovulation and both fell close to zero after ovulation. Given that the fertile interval is before ovulation, methods that anticipate ovulation by several days (such as the assessment of cervical mucus) would be particularly useful for couples who want to time their intercourse either to avoid or facilitate conception.

Time of implantation of the conceptus and loss of pregnancy

BACKGROUND

Implantation of the conceptus is a key step in pregnancy, but little is known about the time of implantation or the relation between the time of implantation and the outcome of pregnancy.

METHODS

We collected daily urine samples for up to six months from 221 women attempting to conceive after ceasing to use contraception. Ovulation was identified on the basis of the ratio of urinary estrogen metabolites to progesterone metabolites, which changes rapidly with luteinization of the ovarian follicle. The time of implantation was defined by the appearance of chorionic gonadotropin in maternal urine.

RESULTS

There were 199 conceptions, for 95 percent of which (189) we had sufficient data for analysis. Of these 189 pregnancies, 141 (75 percent) lasted at least six weeks past the last menstrual period, and the remaining 48 pregnancies (25 percent) ended in early loss. Among the pregnancies that lasted six weeks or more, the first appearance of chorionic gonadotropin occurred 6 to 12 days after ovulation; 118 women (84 percent) had implantation on day 8, 9, or 10. The risk of early pregnancy loss increased with later implantation (P<0.001). Among the 102 conceptuses that implanted by the ninth day, 13 percent ended in early loss. This proportion rose to 26 percent with implantation on day 10, to 52 percent on day 11, and to 82 percent after day 11.

CONCLUSIONS

In most successful human pregnancies, the conceptus implants 8 to 10 days after ovulation. The risk of early pregnancy loss increases with later implantation.

Menstrual and reproductive risk factors for ischemic heart disease

The role of hormones in ischemic heart disease is of considerable interest, but limited data are available pertaining to risk factors associated with endogenous hormones. We examined the association between menstrual and reproductive factors and ischemic heart disease in a cohort of 867 white, college-educated women who prospectively recorded menstrual cycle data for at least 5 years from their early 20s through their menopause. Ischemic heart disease history was obtained from a self-administered (N = 714) or proxy-administered (N = 153) questionnaire completed at a mean age of 73 years. The analysis included 44,899 person-years of follow-up and 45 cases of myocardial infarction, angioplasty, heart bypass surgery, or ischemic heart disease-related mortality. Ischemic heart disease risk decreased with increasing age at menarche (age-adjusted RR 0.76 per year, 95% CI = 0.60-0.95). Considering menstrual cycle characteristics ages 28-32, there was little overall association with length, variability, or bleeding duration. Ischemic heart disease risk increased with later age at first birth (age-adjusted RR 2.90 for ages 33-43 compared with 25-29) and later age at last birth (age-adjusted RR 3.79 for ages > or =40 compared with 35-39), but there was little association with high parity.

Variability of lipid hydroperoxides in pregnant and nonpregnant women

Lipid peroxidation is thought to be important in numerous disease states, including pregnancy complications. Study of its role requires markers, but the variability of available markers in non-diseased populations has not been well-characterized. We examined the variability over time of blood lipid hydroperoxides, as measured by iodometric analysis, in 49 healthy young women, 21 nonpregnant and 28 pregnant. Lipid hydroperoxides from the same woman were very similar from one day to the next but were less stable over periods of a month or more. The correlation between measurements on consecutive days was 0.98; the correlation between measurements a month or more apart was 0.11. Variability over time was not attributable to seasonal effects or, among the pregnant women, to differences over the course of pregnancy. Knowledge of the variability of this and other markers of oxidative damage enables the development of appropriate study designs.

Preimplantation urinary hormone profiles and the probability of conception in healthy women

OBJECTIVE

To examine hormonal predictors of conception in menstrual cycles from normal women.

DESIGN

Longitudinal study.

SETTING

Community.

PATIENT(S)

Two hundred fifteen healthy female volunteers with no known fertility problems who were trying to conceive.

INTERVENTION(S)

Participants recorded menstrual bleeding, sexual intercourse, and collected first morning urine specimens daily from when they stopped contraception until they became pregnant or for 6 months if no clinical pregnancy was achieved. Measurements were made of urinary LH and urinary metabolites of estrogen and progesterone.

MAIN OUTCOME MEASURE(S)

Conception was identified by a sensitive and specific immunoradiometric assay for urinary hCG.

RESULT(S)

Statistical analyses of 189 conception and 409 nonconception cycles controlled for sexual intercourse and interdependence of cycles from the same woman. Conception was more likely in cycles with lower baseline progesterone metabolite levels, higher ovulatory LH, and higher midluteal progesterone. Midluteal estrogen also was elevated in conception cycles when examined without adjusting for other hormone levels, but this finding did not persist after multivariate adjustment.

CONCLUSIONS

Menstrual cycles in normal women vary in their hormonal quality in ways that are predictive of cycle fertility.

Exposure to oxidized nitrogen: lipid peroxidation and neonatal health risk

Pregnant women exposed to extensive environmental contamination by oxidized nitrogen compounds were studied at parturition, their neonatal health status was assessed and the involvement of oxidative stress in pathology was evaluated. Methemoglobin in maternal and cord blood was measured as a biomarker of individual exposure. Blood lipid peroxides and glutathione (reduced and total) were determined as oxidative stress biomarkers. Birthweight, Apgar scores, and clinical diagnosis at birth were used as neonatal health endpoints. Elevated exposure to oxidized nitrogen compounds was associated with increased lipid peroxidation in both maternal and cord blood. Poor birth outcome was associated with high blood lipid peroxides. Controlling for maternal age, parity, and smoking did not affect the relationships materially. The results showed that maternal/fetal exposure to oxidized nitrogen compounds is associated with increased risk of adverse birth outcome and suggest a role of oxidative damage in the pathogenic pathway.

Post-ovulatory ageing of the human oocyte and embryo failure

We carried out a prospective study of 221 healthy women who were attempting pregnancy. During the study, women collected daily urine samples and kept daily records of intercourse. Ovulation and early pregnancy losses were later identified by immunoassays of urinary human chorionic gonadotrophin and steroid metabolites. We have used these data to examine whether the risk of early pregnancy loss was higher with post-ovulatory ageing of the oocyte. 192 pregnancies were ranked by the probability that the oocyte might have aged before fertilization. There was a statistically significant increase in the risk of early loss as the likelihood of oocyte ageing increased (P < 0.05). No similar risk was observed for clinical miscarriages. Post-ovulatory ageing of the oocyte prior to fertilization may cause early pregnancy failure in humans as it does in several other mammalian species.

Preimplantation hormonal differences between the conception and non-conception menstrual cycles of 32 normal women

We compared daily urinary concentrations of oestrogen and progesterone metabolites in paired menstrual cycles (conception and non-conception) from 32 women. Volunteers with no known fertility problems were enrolled in the study at the time they began trying to become pregnant. They collected first-morning urine specimens and kept daily records of menstrual bleeding and sexual intercourse for 6 months or until they became clinically pregnant. Intercourse in non-conception cycles was close to the time of ovulation so that failure to conceive was caused by factors other than poorly timed intercourse. Compared with non-conception cycles, conception cycles had a steeper early luteal rise in progesterone and higher mid-luteal oestrogen and progesterone concentrations. These hormonal characteristics may be markers of better quality cycles, but because all these differences were in the luteal phase, we cannot rule out the possibility that the preimplantation embryo had stimulated early increases in steroid production. We propose an analysis strategy that could help support or refute the importance of preimplantation embryonic signalling, but our small sample size limits our own conclusions about this mechanism.

Breast cancer survival and the timing of tumor removal during the menstrual cycle

In a retrospective cohort study of 262 premenopausal breast cancer patients treated at the Mayo Clinic between 1965 and 1985, we investigated whether survival was associated with the timing of tumor removal during the menstrual cycle. Participants were women < or = 50 years old who had not used exogenous hormones, been pregnant, been lactating, or given birth within 6 months of diagnosis. The menstrual cycle day at surgery was used to assign women to group 1 (cycle days 0-7), group 2 (cycle days 8-15), or group 3 (after cycle day 15). Cox proportional hazards analysis adjusting for age at diagnosis, stage, tumor size, grade, and node involvement showed a nonsignificantly worse survival for group 2 than for group 3 [hazard ratio (HR), 1.41; 95% confidence interval (CI), 0.89-2.23]. Stratification revealed that the association between survival and timing of tumor removal during the menstrual cycle was slightly stronger among patients with stage II disease (adjusted HR, 1.56; 95% CI, 0.92-2.63). The association was the same among patients with stage II disease and node involvement (adjusted HR, 1.57; 95% CI, 0.82-3.03). Prospective studies using hormone measurements to define menstrual cycle status more accurately than the reported day of the menstrual cycle could provide further insight about the postulated association.

Time to pregnancy and preterm delivery

OBJECTIVE

To test whether subfertile women may be at higher risk of preterm delivery.

METHODS

We used data from two population-based cohort studies on risk factors and pregnancy outcome for approximately 20,000 deliveries in three major Danish obstetric departments. The Aalborg-Odense study comprised all pregnant women attending routine antenatal care at two obstetric departments from 1984 to 1987. In all, 11,850 women (86%) filled in a questionnaire at about 36 weeks' gestation. The Aarhus study addressed women at the routine visit near 16 weeks' gestation from 1989 to 1991; a study questionnaire was returned by 6857 (80%). Both studies excluded women with chronic illnesses, multiple fetuses, and inability to speak Danish. Only women with planned pregnancies were included in the analysis. In all, 8855 and 3985 women from Aalborg-Odense and Aarhus, respectively, were eligible for the analyses. In both cohorts, women were categorized according to their waiting time to pregnancy (0-6 months, 7-12 months, and greater than 1 year) and according to examination or treatment for infertility (yes, no). Preterm delivery was defined as birth before 37 completed weeks.

RESULTS

Compared with women who tried for 6 months or less before they conceived, women who tried for 7-12 months had 1.3 times (95% confidence interval [CI] 0.8, 2.1) the adjusted risk of preterm delivery in both cohorts, and women with a time to pregnancy of greater than 12 months had adjusted relative risks for preterm delivery of 1.6 (95% CI 1.1, 2.2) for Aalborg-Odense and 1.7 (95% CI 1.1, 2.6) for Aarhus. The results remained similar after excluding women with infertility treatment.

CONCLUSIONS

Pregnant women with subfertility and clinically defined infertility are more prone to preterm delivery, even in the absence of infertility treatment.

Assessment of reproductive disorders and birth defects in communities near hazardous chemical sites. II. Female reproductive disorders

Members of the workgroup on female reproductive disorders discussed methods to evaluate five principal functions: menstrual dysfunction, infertility, pregnancy loss, lactation disorders, and pregnancy complications. To test each function, a nested strategy was considered, based on progressive levels of effort available to conduct field investigations. This strategy was analogous to the three-tier classification of biomarkers used by other workshops. The lowest level of effort, corresponding to Tier 1, consists only of questionnaires, diaries, and reviews of maternal and infant medical records. The medium level of effort (Tier 2) collects data from questionnaires and diaries, and some biologic specimens. Suggested laboratory analyses included measurement of progesterone in saliva and several glycoprotein hormones in urine that evaluate menstrual dysfunction, infertility, and pregnancy loss. The highest level of effort (Tier 3) involves prospective collection of diary information and simultaneous collection of biological specimens.