The Use of Time to Pregnancy for Estimating and Monitoring Human Fecundity From Demographic and Health Surveys.

BACKGROUND: Available studies on the prevalence of infertility have proved to have certain limitations, with a scarcity of population-based studies and inconsistent reporting from surveys in countries at all income levels. We wanted to test the applicability of the current duration approach to data from the important Demographic and Health Surveys (DHS) program, funded by USAID since its inception in 1985, https://dhsprogram.com/. METHODS: The current duration approach assumes that there is a well-defined time of initiation of attempts to get pregnant and defines the current duration of a still ongoing pregnancy attempt as the time interval from initiation to interview. The DHS interviews do not have an explicit question about initiation. We focused on nullipari and substituted date of "establishment of relationship with current partner" for initiation. Our study used the current duration approach on 15 datasets from DHS during 2002-2016 in eight different countries from sub-Saharan Africa, Asia, and Latin America. RESULTS: Well-established statistical techniques for current duration data yielded results that for some countries postulated surprisingly long median times to pregnancy and surprisingly high estimates of infertility prevalence. Further study of the data structures revealed serious deviations from expected patterns, in contrast to our earlier experience from surveys in France and the United States where participants were asked explicitly about time of initiation of attempts to become pregnant. CONCLUSIONS: Using cohabitation as a proxy for the initiation of attempts to get pregnant is too crude. Using the current duration approach with DHS data will require more explicit questions during the DHS interviews about initiation of pregnancy attempt.

High preharvest donor Foxp3 mRNA level predicts late relapse of acute lymphoblastic leukaemia after haematopoietic stem cell transplantation.

OBJECTIVES: The curative effect of allogeneic haematopoietic stem cell transplantation (HSCT) for acute leukaemia is due in part to the donor T cell-mediated graft-versus-leukaemia immune reaction (GvL). Several studies have suggested that donor CD25+CD4+Foxp3+regulator T cells (Tregs) may decrease graft-versus-host disease (GvHD) without abrogating GVL. This notion may need modification in acute lymphoblastic leukaemia (ALL). METHODS: Foxp3 mRNA level was measured by qPCR in preharvest donor blood CD4+ T cells. The study comprised 45 patients with ALL in 1st or 2nd CR who received myeloablative HSCT using T-replete bone marrow grafts. RESULTS: Relapse occurred in 17 patients median 363 days after HSCT. The relapse risk was estimated by Cox univariate and multivariate proportional hazard regression. The proportionality assumption was met by analysing the preharvest donor Foxp3 mRNA level as a time-dependent covariate. Early relapse was not modified by the Foxp3 mRNA level. However, a higher Foxp3 mRNA level was associated with a significantly increased relapse risk after day 363 after transplantation, compatible with inhibition of GvL. In contrast, a higher preharvest donor CD4+ T-cell concentration was associated with reduced relapse risk. CONCLUSION: A higher preharvest donor Foxp3 mRNA level may be predictive of late ALL relapse after HSCT.

A Systematic Comparison of Designs to Study Human Fecundity.

BACKGROUND: Several epidemiologic designs allow studying fecundability, the monthly probability of pregnancy occurrence in noncontracepting couples in the general population. These designs may, to varying extents, suffer from attenuation bias and other biases. We aimed to compare the main designs: incident and prevalent cohorts, pregnancy-based, and current duration approaches. METHODS: A realistic simulation model produced individual reproductive lives of a fictitious population. We drew random population samples according to each study design, from which the cumulative probability of pregnancy was estimated. We compared the abilities of the designs to highlight the impact of an environmental factor influencing fecundability, relying on the Cox model with censoring after 12 or 6 months. RESULTS: Regarding the estimation of the cumulative probability of pregnancy, the pregnancy-based approach was the most prone to bias. When we considered a hypothetical factor associated with a hazard ratio (HR) of pregnancy of 0.7, the estimated HR was in the 0.78-0.85 range, according to designs. This attenuation bias was largest for the prevalent cohort and smallest for the current duration approach, which had the largest variance. The bias could be limited in all designs by censoring durations at 6 months. CONCLUSION: Attenuation bias in HRs cannot be ignored in fecundability studies. Focusing on the effect of exposures during the first 6 months of unprotected intercourse through censoring removes part of this bias. For risk factors that can accurately be assessed retrospectively, retrospective fecundity designs, although biased, are not much more strongly so than logistically more intensive designs entailing follow-up.

Relation Between Infant Microbiota and Autism?: Results from a National Cohort Sibling Design Study.

BACKGROUND: Hypotheses concerning adverse effects of changes in microbiota have received much recent attention, but unobserved confounding makes them difficult to test. We investigated whether surrogate markers for potential adverse microbiota change in infancy affected autism risk, addressing unobserved confounding using a sibling study design. METHODS: This is a population-based, prospective cohort study including all singleton live births in Denmark from 1997 to 2010. The exposure variables were cesarean delivery and antibiotic use in the first 2 years of life. The outcome was a subsequent autism diagnosis. We used the between- and within-sibling model and compared it with sibling-stratified Cox models and simpler standard Cox models that ignored sibship. RESULTS: Of our study population including 671,606 children, who were followed for up to 15 years (7,341,133 person-years), 72% received antibiotics, 17.5% were delivered by cesarean, and 1.2% (8,267) developed autism. The standard Cox models predicted that both cesarean (compared with vaginal) delivery and antibiotics increased the risk of autism. In the sibling-stratified Cox model, only broader spectrum antibiotics were associated with increased risk of autism: hazard ratio (HR) = 1.16 (95% confidence interval = 1.01, 1.36). The between-within model estimated no exposure effects: intrapartum cesarean HR = 1.06 (0.89, 1.26); prelabor cesarean HR = 0.97 (0.83, 1.15); exclusively penicillin HR = 1.05 (0.93, 1.18); and broader spectrum antibiotics HR = 1.05 (0.95, 1.16). CONCLUSIONS: The between-within model rendered more precise estimates than sibling-stratified Cox models, and we believe that it also provided more valid estimates. Results from these preferred models do not support a causal relation between antibiotic treatment during infancy, cesarean delivery, and autism. See video abstract at, http://links.lww.com/EDE/B432.

Investigating the effects of cesarean delivery and antibiotic use in early childhood on risk of later attention deficit hyperactivity disorder.

BACKGROUND: Increasing attention deficit hyperactivity disorder (ADHD) incidence has been proposed to be caused by factors influencing microbiota in early life. We investigated the potential causality between ADHD and two surrogate markers for changes in children's microbiota: birth delivery mode and early childhood antibiotic use. METHOD: This population-based, prospective cohort study linked nationwide registers of data for native Danish singleton live births in Denmark from 1997 to 2010. Exposure variables were delivery mode and antibiotic use during the first 2 years of life. The main outcome measure was ADHD diagnosis or redeemed ADHD medication prescriptions. For statistical analysis, we used both advanced sibling models and a more traditional approach. RESULTS: We included 671,592 children, followed from their second birthday in the period 1999-2014 for 7,300,522 person-years. ADHD was diagnosed in 17,971. In total, 17.5% were born by cesarean delivery, and 72% received antibiotic treatment within their first 2 years of life. In the adjusted between-within sibling survival model, mode of delivery or antibiotics had no effect on ADHD when compared with vaginal delivery or no antibiotic treatment as hazard ratios were 1.09 (95% confidence interval 0.97-1.24) for intrapartum cesarean, 1.03 (0.91-1.16) for prelabor cesarean, 0.98 (0.90-1.07) for penicillin, and 0.99 (0.92-1.06) for broader spectrum antibiotics. In a sibling-stratified Cox regression, intrapartum cesarean was associated with increased ADHD risk, but other exposures were not. In a descriptive, nonstratified Cox model, we found increased risk for ADHD for all exposures. CONCLUSIONS: Detailed family confounder control using the superior between-within model indicates that cesarean delivery or use of antibiotics during the first 2 years of life does not increase ADHD risk. Therefore, our study suggests that changes in children's microbiota related to cesarean delivery or antibiotic use, do not cause ADHD.

Prevalent cohort studies and unobserved heterogeneity.

Consider lifetimes originating at a series of calendar times [Formula: see text]. At a certain time [Formula: see text] a cross-sectional sample is taken, generating a sample of current durations (backward recurrence times) of survivors until [Formula: see text] and a prevalent cohort study consisting of survival times left-truncated at the current durations. A Lexis diagram is helpful in visualizing this situation. Survival analysis based on current durations and prevalent cohort studies is now well-established as long as all covariates are observed. The general problems with unobserved covariates have been well understood for ordinary prospective follow-up studies, with the good help of hazard rate models incorporating frailties: as for ordinary regression models, the added noise generates attenuation in the regression parameter estimates. For prevalent cohort studies this attenuation remains, but in addition one needs to take account of the differential selection of the survivors from initiation [Formula: see text] to cross-sectional sampling at [Formula: see text]. This paper intends to survey the recent development of these matters and the consequences for routine use of hazard rate models or accelerated failure time models in the many cases where unobserved heterogeneity may be an issue. The study was inspired by concrete problems in the study of time-to-pregnancy, and we present various simulation results inspired by this particular application.

Risk of Stroke With Various Types of Menopausal Hormone Therapies: A National Cohort Study.

BACKGROUND AND PURPOSE: Double-blind randomized studies on the effects of oral postmenopausal hormone therapies were stopped mainly because of increased risk of stroke. We aimed to assess the risk of all strokes and various subtypes associated with hormone therapy and explore the influence of regimens and routes of administration. METHODS: A national historical cohort of women aged 51 to 70 years from 1995 to 2010 was established by linking 5 Danish registries. The National Registry of Medicinal Product Statistics provided information on hormone therapy exposure and the National Patient or Cause of Death Registries supplied data regarding stroke diagnoses (ischemic/hemorrhagic/subarachnoid hemorrhage). Multiply adjusted rate ratios with time-varying covariates were fitted in Poisson regression models. RESULTS: Of the 980 003 included women, 20 199 suffered a stroke (78% ischemic, 12% hemorrhagic, and 10% subarachnoid hemorrhage). In total, 36% of women used hormone therapy. Current use conferred a relative rate of 1.16 (95% confidence interval, 1.12-1.22). Compared with never users, the increased rate ratio of all stroke with continuous, cyclic combined estrogen/progestin, and estrogen only oral therapies were 1.29 (95% confidence interval, 1.21-1.37), 1.11 (95% confidence interval, 1.04-1.20), and 1.18 (95% confidence interval, 1.10-1.26), respectively. The increased risk was because of ischemic stroke, but not hemorrhagic stroke. Transdermal application of hormone therapy was not associated with risk of stroke. Vaginal estrogen was associated with a decreased risk of stroke. CONCLUSIONS: In a national setting, we found an increased risk of stroke, based on ischemic stroke, with oral hormone therapies that was comparable to findings from randomized studies. We found no risk of stroke with transdermal application and a reduced risk with vaginal estrogen.

The influence of hormone therapies on type I and II endometrial cancer: A nationwide cohort study.

The influence of hormone therapy (HT) on risk for endometrial cancer is still casting which type of HT the clinicians recommend. It is unrevealed if HT has a differential influence on Type I versus Type II endometrial tumors, and little is known about the influence of, e.g., different routes of administration and about the influence of tibolone. We followed all Danish women aged 50-79 years without previous cancer or hysterectomy (n = 914,595) during 1995-2009. From the National Prescription Register, we computed HT exposures as time-dependent covariates. Incident endometrial cancers (n = 6,202) were identified from the National Cancer Registry: 4,972 Type I tumors and 500 Type II tumors. Incidence rate ratios (RRs) and 95% confidence intervals (Cls) were estimated by Poisson regression. Compared with women never on HT, the RR of endometrial cancer was increased with conjugated estrogen: 4.27 (1.92-9.52), nonconjugated estrogen: 2.00 (1.87-2.13), long cycle combined therapy: 2.89 (2.27-3.67), cyclic combined therapy: 2.06 (1.88-2.27), tibolone 3.56 (2.94-4.32), transdermal estrogen: 2.77 (2.12-3.62) and vaginal estrogen: 1.96 (1.77-2.17), but not with continuous combined therapy: 1.02 (0.87-1.20). In contrast, the risk of Type II tumors appeared decreased with continuous combined therapy: 0.45 (0.20-1.01), and estrogen therapy implied a nonsignificantly altered risk of 1.43 (0.85-2.41). Our findings support that continuous combined therapy is risk free for Type I tumors, while all other hormone therapies increase risk. In contrast, Type II endometrial cancer was less convincingly associated with hormone use, and continuous combined therapy appeared to decrease the risk.

A Simulation Platform for Quantifying Survival Bias: An Application to Research on Determinants of Cognitive Decline.

Bias due to selective mortality is a potential concern in many studies and is especially relevant in cognitive aging research because cognitive impairment strongly predicts subsequent mortality. Biased estimation of the effect of an exposure on rate of cognitive decline can occur when mortality is a common effect of exposure and an unmeasured determinant of cognitive decline and in similar settings. This potential is often represented as collider-stratification bias in directed acyclic graphs, but it is difficult to anticipate the magnitude of bias. In this paper, we present a flexible simulation platform with which to quantify the expected bias in longitudinal studies of determinants of cognitive decline. We evaluated potential survival bias in naive analyses under several selective survival scenarios, assuming that exposure had no effect on cognitive decline for anyone in the population. Compared with the situation with no collider bias, the magnitude of bias was higher when exposure and an unmeasured determinant of cognitive decline interacted on the hazard ratio scale to influence mortality or when both exposure and rate of cognitive decline influenced mortality. Bias was, as expected, larger in high-mortality situations. This simulation platform provides a flexible tool for evaluating biases in studies with high mortality, as is common in cognitive aging research.

Prelabor Cesarean Section and Risk of Childhood Type 1 Diabetes: A Nationwide Register-based Cohort Study.

BACKGROUND: Unfavorable conditions associated with cesarean section may influence the risk of type 1 diabetes in offspring, but results from studies are conflicting. We aimed to evaluate the association between prelabor cesarean section and risk of childhood type 1 diabetes. METHODS: A Danish nationwide cohort study followed all singletons born during 1982-2010. Four national registers provided information on mode of delivery, outcome, and confounders. The risk of childhood type 1 diabetes with onset before the age of 15 years was assessed by Cox regression. A total of 1,760,336 singletons contributed 20,436,684 person-years, during which 4,400 were diagnosed with childhood type 1 diabetes. RESULTS: The hazard ratio (HR) for childhood type 1 diabetes was increased in children delivered by prelabor cesarean section compared with vaginal delivery when adjusted for year of birth, parity, sex, parental age, and education and paternal type 1 diabetes status at childbirth (HR = 1.2; 95% confidence interval [CI] = 1.0, 1.3), but not after additional adjustment for maternal type 1 diabetes status at childbirth (HR = 1.1; 95% CI = 0.95, 1.2). Delivery by intrapartum cesarean section was not associated with childhood type 1 diabetes. Paternal type 1 diabetes was a stronger risk factor for childhood type 1 (HR = 12; 95% CI = 10, 14) than maternal type 1 diabetes (HR = 6.5; 95% CI = 5.2, 8.0). CONCLUSIONS: Delivery by prelabor cesarean section was not associated with an increased risk of childhood type 1 diabetes in the offspring.

The influence of hormone therapies on colon and rectal cancer.

Exogenous sex hormones seem to play a role in colorectal carcinogenesis. Little is known about the influence of different types or durations of postmenopausal hormone therapy (HT) on colorectal cancer risk. A nationwide cohort of women 50-79 years old without previous cancer (n = 1,006,219) were followed 1995-2009. Information on HT exposures was from the National Prescription Register and updated daily, while information on colon (n = 8377) and rectal cancers (n = 4742) were from the National Cancer Registry. Potential confounders were obtained from other national registers. Poisson regression analyses with 5-year age bands included hormone exposures as time-dependent covariates. Use of estrogen-only therapy and combined therapy were associated with decreased risks of colon cancer (adjusted incidence rate ratio 0.77, 95 % confidence interval 0.68-0.86 and 0.88, 0.80-0.96) and rectal cancer (0.83, 0.72-0.96 and 0.89, 0.80-1.00), compared to never users. Transdermal estrogen-only therapy implied more protection than oral administration, while no significant influence was found of regimen, progestin type, nor of tibolone. The benefit of HT was stronger for long-term hormone users; and hormone users were at lower risk of advanced stage of colorectal cancer, which seems supportive for a causal association between hormone therapy and colorectal cancer.

Thrombotic stroke and myocardial infarction with hormonal contraception.

BACKGROUND: Although several studies have assessed the risk of venous thromboembolism with newer hormonal contraception, few have examined thrombotic stroke and myocardial infarction, and results have been conflicting. METHODS: In this 15-year Danish historical cohort study, we followed nonpregnant women, 15 to 49 years old, with no history of cardiovascular disease or cancer. Data on use of hormonal contraception, clinical end points, and potential confounders were obtained from four national registries. RESULTS: A total of 1,626,158 women contributed 14,251,063 person-years of observation, during which 3311 thrombotic strokes (21.4 per 100,000 person-years) and 1725 myocardial infarctions (10.1 per 100,000 person-years) occurred. As compared with nonuse, current use of oral contraceptives that included ethinyl estradiol at a dose of 30 to 40 µg was associated with the following relative risks (and 95% confidence intervals) for thrombotic stroke and myocardial infarction, according to progestin type: norethindrone, 2.2 (1.5 to 3.2) and 2.3 (1.3 to 3.9); levonorgestrel, 1.7 (1.4 to 2.0) and 2.0 (1.6 to 2.5); norgestimate, 1.5 (1.2 to 1.9) and 1.3 (0.9 to 1.9); desogestrel, 2.2 (1.8 to 2.7) and 2.1 (1.5 to 2.8); gestodene, 1.8 (1.6 to 2.0) and 1.9 (1.6 to 2.3); and drospirenone, 1.6 (1.2 to 2.2) and 1.7 (1.0 to 2.6), respectively. With ethinyl estradiol at a dose of 20 µg, the corresponding relative risks according to progestin type were as follows: desogestrel, 1.5 (1.3 to 1.9) and 1.6 (1.1 to 2.1); gestodene, 1.7 (1.4 to 2.1) and 1.2 (0.8 to 1.9); and drospirenone, 0.9 (0.2 to 3.5) and 0.0. For transdermal patches, the corresponding relative risks were 3.2 (0.8 to 12.6) and 0.0, and for a vaginal ring, 2.5 (1.4 to 4.4) and 2.1 (0.7 to 6.5). CONCLUSIONS: Although the absolute risks of thrombotic stroke and myocardial infarction associated with the use of hormonal contraception were low, the risk was increased by a factor of 0.9 to 1.7 with oral contraceptives that included ethinyl estradiol at a dose of 20 µg and by a factor of 1.3 to 2.3 with those that included ethinyl estradiol at a dose of 30 to 40 µg, with relatively small differences in risk according to progestin type. (Funded by the Danish Heart Association.).

Risk of breast cancer in relation to combined effects of hormone therapy, body mass index, and alcohol use, by hormone-receptor status.

BACKGROUND: Alcohol consumption, increased body mass index (BMI), and hormone therapy are risk factors for postmenopausal breast cancer, but their combined effects are not well understood. Because hormone therapy is effective for the relief of menopausal symptoms, the identification of "high-risk" users is important for therapeutic reasons. We investigated interactions between hormone therapy use and alcohol-use/high BMI status in relation to invasive breast cancer risk, both overall and according to estrogen receptor (ER) status. METHODS: Two Danish prospective cohorts were pooled, including 30,789 women ages 50+ years (study period 1981 to 2009). Information on risk factors was obtained in baseline questionnaires. We performed analyses using the Aalen additive hazards model. Serum estradiol and testosterone measurements were obtained in a subsample of approximately 1000 women. RESULTS: During 392,938 person-years of follow-up, 1579 women developed invasive breast cancer. Among nonusers of hormone therapy, the risk of breast cancer was slightly increased with overweight/obesity and increasing alcohol consumption. Compared with normal-weight nonusers, the risk of breast cancer was higher in hormone therapy users across all BMI strata (P for interaction = 0.003). A markedly higher risk of breast cancer was also observed for alcohol combined with hormone therapy use compared with abstinent nonusers (P for interaction = 0.02). These effects were primarily restricted to ER-positive cases. Combined effects of hormone therapy/high BMI and hormone therapy/alcohol on serum estradiol and testosterone supported the hypothesis of a hormonal pathway linking these exposures to breast cancer. CONCLUSION: These analyses suggest an increased risk of breast cancer associated with hormone therapy use-a risk that may be particularly strong among women consuming alcohol.

The current duration design for estimating the time to pregnancy distribution: a nonparametric Bayesian perspective.

This paper was inspired by the studies of Niels Keiding and co-authors on estimating the waiting time-to-pregnancy (TTP) distribution, and in particular on using the current duration design in that context. In this design, a cross-sectional sample of women is collected from those who are currently attempting to become pregnant, and then by recording from each the time she has been attempting. Our aim here is to study the identifiability and the estimation of the waiting time distribution on the basis of current duration data. The main difficulty in this stems from the fact that very short waiting times are only rarely selected into the sample of current durations, and this renders their estimation unstable. We introduce here a Bayesian method for this estimation problem, prove its asymptotic consistency, and compare the method to some variants of the non-parametric maximum likelihood estimators, which have been used previously in this context. The properties of the Bayesian estimation method are studied also empirically, using both simulated data and TTP data on current durations collected by Slama et al. (Hum Reprod 27(5):1489-1498, 2012).

Time trends in biological fertility in Western Europe.

We investigated trends in biological fertility in a comprehensive analysis of 5 major European data sets with data on time to pregnancy (TTP) and proportion of contraceptive failures. In particular, we distinguished a period effect from a birth cohort effect (lifelong tendency) in both sexes. Attempts at conception not resulting in birth were excluded. We analyzed data on pregnancies occurring in 9,247 couples between 1953 and 1993 and performed sensitivity analyses to check the robustness of findings. Separate analyses of each time effect showed an increasing fertility trend. Mutually adjusted analyses demonstrated that this rise was visible as a male cohort effect for both TTP and contraceptive failure. On the other hand, the female birth cohort effect showed a slight fall in the first half of the study period for both TTP and contraceptive failure. As a period effect, fertility remained generally stable, the slight trends in TTP and contraceptive failure being in opposite directions, likely indicating an artifact. The rising trend accords with most previous evidence. The increasing trend in male fertility does not contradict the previously reported semen quality deterioration, the effects of which are calculated to be small. The declining female fertility accords with a falling dizygotic twinning rate during the same period.

Nonparametric estimation in an "illness-death" model when all transition times are interval censored.

We develop nonparametric maximum likelihood estimation for the parameters of an irreversible Markov chain on states {0,1,2} from the observations with interval censored times of 0 → 1, 0 → 2 and 1 → 2 transitions. The distinguishing aspect of the data is that, in addition to all transition times being interval censored, the times of two events (0 → 1 and 1 → 2 transitions) can be censored into the same interval. This development was motivated by a common data structure in oral health research, here specifically illustrated by the data from a prospective cohort study on the longevity of dental veneers. Using the self-consistency algorithm we obtain the maximum likelihood estimators of the cumulative incidences of the times to events 1 and 2 and of the intensity of the 1 → 2 transition. This work generalizes previous results on the estimation in an "illness-death" model from interval censored observations.

Interpretability and importance of functionals in competing risks and multistate models.

The basic parameters in both survival analysis and more general multistate models, including the competing risks model and the illness-death model, are the transition hazards. It is often necessary to supplement the analysis of such models with other model parameters, which are all functionals of the transition hazards. Unfortunately, not all such functionals are equally meaningful in practical contexts, even though they may be mathematically well defined. We have found it useful to check whether the functionals satisfy three simple principles, which may be used as criteria for practical interpretability.

Estimating survival of dental fillings on the basis of interval-censored data and multi-state models.

We aim to compare the life expectancy of a filling in a primary tooth between two types of treatments. We define the probabilities that a dental filling survives without complication until the permanent tooth erupts from beneath (exfoliation). We relate the time to exfoliation of the tooth to the age of the child and the time to failure of the filling to the duration since the treatment. We followed up fillings at repeated examinations where information is collected regarding the filling and the tooth. Several fillings can be placed in the same mouth, possibly by the same dentist. To deal with all these particularities, we propose to use a parametric four-state model with three random effects to take into account the hierarchical cluster structure. For inference, right and interval censoring as well as left truncation have to be dealt with. With the proposed approach, we can conclude that the estimated probability that a filling survives without complication until exfoliation is larger for one treatment than for the other, for all ages of the child at the time of treatment.