Smoking and infertility: multivariable regression and Mendelian randomization analyses in the Norwegian Mother, Father and Child Cohort Study

Di-2-ethylhexyl phthalate (DEHP) exposure increase female infertility

This study explores the relationship between Di-2-ethylhexyl phthalate (DEHP) exposure and female infertility. The analysis included 998 female participants aged between 18 and 44 years. We analyzed data from the National Health and Nutrition Examination Survey (2013-2018) using multiple logistic regression and generalized linear models to assess the impact of DEHP on infertility. Additionally, we employed curve fitting and two-piecewise linear regression models to investigate potential nonlinear correlations, conducting subgroup analyses based on age, BMI, alcohol consumption, smoking status, hypertension, and diabetes. Our results, after adjusting for confounders, revealed a positive association between DEHP exposure and infertility. This association was significant whether DEHP was treated as a continuous variable (odds ratio OR = 1.28, 95 % confidence interval CI: 1.08-1.52, P = 0.0072) or as a categorical variable (P for trend = 0.0038). A non-linear relationship was identified, with an inflection point at - 3.35 (∑DEHP = 0.0981 × 10-9 mol/mg creatinine). Effect sizes were 1.55 (1.01-2.36) on the left side of the inflection point and 0.73 (0.43-1.23) on the right side. Subgroup analysis indicated that the correlation was consistent across stratified variables. In conclusion, our findings suggest a non-linear association between DEHP exposure and female infertility, with a positive correlation within a specific dose range, but no further increase in risk beyond a certain threshold.

Prepubescent Electronic Cigarette Exposure Affects Sexual Motivation and Puberty in Female But Not Male Long-Evans Rats

INTRODUCTION

A method for delivering vaporized nicotine to animals has been developed using e-cigarette devices. The present experiment was designed to measure the effects of e-cigarette nicotine on pubertal onset and development of reproductive behavior in female and male Long-Evans rats.

AIM AND METHODS

Rats received daily 10-min sessions of electronic-cigarette vaporized nicotine (5% Virginia Tobacco JUUL Pods) or room air in a whole-body exposure chamber (postnatal day 28-31). Pubertal onset was monitored daily (ie, vaginal opening in females, preputial separation in males). Two weeks later, rats were tested for sexual motivation using the partner-preference paradigm, whereby subjects were given the opportunity to approach either a sexual partner or a same-sex social partner. Four weeks later, partner preference was assessed again, 10 min after rats were re-exposed to their same prepubertal treatment.

RESULTS

We found that prepubescent electronic-cigarette vaporized nicotine disrupted puberty and sexual motivation in female but not male rats. In vaped females, vaginal opening was delayed and less time was spent with the male stimulus compared to room-air controls. In contrast, no effect of e-cigarette vapor was observed on pubertal onset or on any measures of sexual behavior in male rats. No effects were observed in either female or male rats on the second partner-preference test.

CONCLUSIONS

Prepubescent vaporized nicotine affected the development of reproductive physiology and behavior in female rats but not in male rats, whereas an additional acute exposure to nicotine vapor had no effect in either female or male adult rats.

IMPLICATIONS

Given the prevalence of increasingly younger users, more animal research is needed to explore the effects of e-cigarette smoking on multiple developmental systems including reproductive physiology and behavior. This model could be useful in exploring multiple behavioral and physiological endpoints in both sexes. Adjustments to the duration of exposure and control conditions will be necessary for future experiments to best model human use.

Factors influencing natural fecundity in fertile couples: a survey of puerperae and their partners

RESEARCH QUESTION

What is the fecundity rate among fertile couples, and which factors influence it?

DESIGN

Retrospective study of all puerperae attending Cruces University Hospital Human Reproduction Unit over 9 months. An anonymous questionnaire was circulated to all patients, and 2510 valid completed questionnaires were collected. The main inclusion criterion was natural conception resulting in delivery. Pregnancies resulting from ART and contraceptive method failure were excluded. Investigated parameters were time to pregnancy, age and smoking (in women and men), previous pregnancies and intercourse frequency. A mathematical formula was developed to predict the per-month fecundity rate (PMFR).

RESULTS

The cumulative fecundity rate was 29.08%, 54.26%, 68.61%, 89.88%, 96.95% and 98.63% (at 1, 3, 6, 12, 24 and 36 months); between 12 and 36 months, the average PMFR ranged from 8.53-7.48%. Only 1.68% of pregnancies occurred between 24 and 36 months, and only 1.37% thereafter. The best fecundity markers were obtained in the group who had sexual intercourse seven to eight times a week. Women and men younger than 25 years had lower fecundity markers than those aged between 25 and 40 years.

CONCLUSIONS

Fertile couples have a non-negligible per-month fecundity rate between 12 and 36 months, which should be considered when planning fertility studies. The lower fecundity rate observed in women and men aged younger than 25 years deserves more study. Coital frequencies of more than two or three times a week did not affect the fecundity rate and was better with frequencies of seven to eight times a week.

Cardiovascular disease risk factors and infertility: multivariable analyses and one-sample Mendelian randomization analyses in the Trøndelag Health Study

STUDY QUESTION

Are cardiovascular disease (CVD) risk factors causally associated with higher risk of infertility among women and men?

SUMMARY ANSWER

We found evidence to support a causal relationship between smoking initiation and history of infertility in women.

WHAT IS KNOWN ALREADY

Several CVD risk factors are associated with history of infertility. Previous studies using Mendelian randomization (MR) further support a causal relationship between BMI and infertility in women.

STUDY DESIGN SIZE DURATION

We used data from the Trøndelag Health Study (HUNT) in Norway, a prospective population-based cohort study, including 26 811 women and 15 598 men participating in three survey collections in 1995-1997 (HUNT2), 2006-2008 (HUNT3), and 2017-2019 (HUNT4).

PARTICIPANTS/MATERIALS SETTING METHODS

Our outcome was women's self-reported history of infertility, defined as ever having tried to conceive for 12 months or more or having used ART. We assigned the history of infertility reported by women to their male partners; therefore, the measure of infertility was on the couple level. We used both conventional multivariable analyses and one-sample MR analyses to evaluate the association between female and male CVD risk factors (including BMI, blood pressure, lipid profile measurements, and smoking behaviours) and history of infertility in women and men, separately.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 4702 women (18%) and 2508 men (16%) were classified with a history of infertility. We found a higher risk of infertility among female smokers compared to non-smokers in both multivariable and MR analyses (odds ratio (OR) in multivariable analysis, 1.20; 95% CI, 1.12-1.28; OR in MR analysis, 1.13; CI, 1.02-1.26), and potentially for higher BMI (OR in multivariable analysis, 1.13; CI, 1.09-1.18; OR in MR analysis, 1.11, CI, 0.92-1.34). In multivariable analysis in women, we also found evidence of associations between triglyceride levels, high-density lipoprotein cholesterol, lifetime smoking index, and smoking intensity with higher risk of infertility. However, these results were not consistent in MR analyses. We found no robust or consistent associations between male CVD risk factors and infertility.

LIMITATIONS REASONS FOR CAUTION

Our main limitation was that the CVD risk factors measured might not adequately capture the relevant time periods for when couples were trying to conceive. Additionally, we did not have information on causes of infertility in either women or men.

WIDER IMPLICATIONS OF THE FINDINGS

Women with infertility could have a worse CVD risk factor profile and thus public health interventions aimed at reducing the impact of some CVD risk factors, such as smoking and BMI, could reduce the burden of infertility. However, additional MR studies of the relationship between CVD risk factors and infertility with a larger sample size would be of value.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by a grant from the European Research Council under the European Union's Horizon 2020 research and innovation program (grant agreements no. 947684). This research was also supported by the Research Council of Norway through its Centres of Excellence funding scheme (project no. 262700) and partly funded by the Research Council of Norway, project: Women's fertility-an essential component of health and well-being (project no. 320656). D.A.L. and A.F. work in a unit that is supported by the University of Bristol and the UK Medical Research Council (MC_UU_00011/6). D.A.L.'s contribution to the article is supported by the European Research Council (101021566), the British Heart Foundation (CH/F/20/90003 and AA/18/7/34219). S.B.'s contribution to the article is supported by the Wellcome Trust (225790/Z/22/Z). B.M.B. is funded by The Liaison Committee for education, research and innovation in Central Norway; and the Joint Research Committee between St. Olavs Hospital and the Faculty of Medicine and Health Sciences, NTNU. The genotyping in HUNT was financed by the National Institute of Health (NIH); University of Michigan; The Research Council of Norway; The Liaison Committee for education, research and innovation in Central Norway; and the Joint Research Committee between St. Olavs Hospital and the Faculty of Medicine and Health Sciences, NTNU. None of the funding organizations influenced the study design, reporting, or interpretation of results. The views expressed in the present article are those of the authors and not necessarily any acknowledged funding organization. D.A.L. reports grants from Medtronic Ltd and Roche Diagnostics outside the submitted work. The other authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Preconception depression reduces fertility: a couple-based prospective preconception cohort

STUDY QUESTION

Is preconception depression associated with time to pregnancy (TTP) and infertility?

SUMMARY ANSWER

Couples with preconception depression needed a longer time to become pregnant and exhibited an increased risk of infertility.

WHAT IS KNOWN ALREADY

Preconception depression in women contributes to impaired fertility in clinical populations. However, evidence from the general population-especially based on couples-is relatively scant.

STUDY DESIGN SIZE DURATION

A couple-based prospective preconception cohort study was performed in 16 premarital examination centers between April 2019 and June 2021. The final analysis included 16 521 couples who tried to conceive for ≤6 months at enrollment. Patients with infertility were defined as those with a TTP ≥12 months and those who conceived through ART.

PARTICIPANTS/MATERIALS SETTING METHODS

Couples' depression was assessed using the Patient Health Questionnaire-9 at baseline. Reproductive outcomes were obtained via telephone at 6 and 12 months after enrollment. Fertility odds ratios (FORs) and infertility risk ratios (RRs) in different preconception depression groups were analyzed using the Cox proportional-hazard models and logistic regression, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

Of the 16 521 couples analyzed, 10 834 (65.6%) and 746 (4.5%) couples achieved pregnancy within the first 6 months and between the 6th and 12th months, respectively. The median (P25, P75) TTP was 3.0 (2.0, 6.0) months. The infertility rate was 13.01%. After adjusting for potential confounders, in the individual-specific analyses, we found that preconception depression in women was significantly related to reduced odds of fertility (FOR = 0.947, 95% CI: 0.908-0.988), and preconception depression in either men or women was associated with an increased risk of infertility (women: RR = 1.212, 95% CI: 1.076-1.366; men: RR = 1.214, 95% CI: 1.068-1.381); in the couple-based analyses, we found that-compared to couples where neither partner had depression-the couples where both partners had depression exhibited reduced fertility (adjusted FOR = 0.904, 95% CI: 0.838-0.975). The risk of infertility in the group where only the woman had depression and both partners had depression increased by 17.8% (RR = 1.178, 95% CI: 1.026-1.353) and 46.9% (RR = 1.469, 95% CI: 1.203-1.793), respectively.

LIMITATIONS REASONS FOR CAUTION

Reporting and recall bias were unavoidable in this large epidemiological study. Some residual confounding factors-such as the use of anti-depressants and other medications, sexual habits, and prior depressive and anxiety symptoms-remain unaddressed. We used a cut-off score of 5 to define depression, which is lower than prior studies. Finally, we assessed depression only at baseline, therefore we could not detect effects of temporal changes in depression on fertility.

WIDER IMPLICATIONS OF THE FINDINGS

This couple-based study indicated that preconception depression in individuals and couples negatively impacts couples' fertility. Early detection and intervention of depression to improve fertility should focus on both sexes.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from the National Natural Science Foundation of China (No. 82273638) and the National Key Research and Development Program of China (No. 2018YFC1004201). All authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Impaired glucose tolerance and cardiovascular risk factors in relation to infertility: a Mendelian randomization analysis in the Norwegian Mother, Father, and Child Cohort Study

STUDY QUESTION

Are impaired glucose tolerance (as measured by fasting glucose, glycated hemoglobin, and fasting insulin) and cardiovascular disease risk (as measured by low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, systolic blood pressure, and diastolic blood pressure) causally related to infertility?

SUMMARY ANSWER

Genetic instruments suggest that higher fasting insulin may increase infertility in women.

WHAT IS KNOWN ALREADY

Observational evidence suggests a shared etiology between impaired glucose tolerance, cardiovascular risk, and fertility problems.

STUDY DESIGN, SIZE, DURATION

This study included two-sample Mendelian randomization (MR) analyses, in which we used genome-wide association summary data that were publicly available for the biomarkers of impaired glucose tolerance and cardiovascular disease, and sex-specific genome-wide association studies (GWASs) of infertility conducted in the Norwegian Mother, Father, and Child Cohort Study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

There were 68 882 women (average age 30, involved in 81 682 pregnancies) and 47 474 of their male partners (average age 33, 55 744 pregnancies) who had available genotype data and who provided self-reported information on time-to-pregnancy and use of ARTs. Of couples, 12% were infertile (having tried to conceive for ≥12 months or used ARTs to conceive). We applied the inverse variance weighted method with random effects to pool data across variants and a series of sensitivity analyses to explore genetic instrument validity. (We checked the robustness of genetic instruments and the lack of unbalanced horizontal pleiotropy, and we used methods that are robust to population stratification.) Findings were corrected for multiple comparisons by the Bonferroni method (eight exposures: P-value < 0.00625).

MAIN RESULTS AND THE ROLE OF CHANCE

In women, increases in genetically determined fasting insulin levels were associated with greater odds of infertility (+1 log(pmol/l): odds ratio 1.60, 95% CI 1.17 to 2.18, P-value = 0.003). The results were robust in the sensitivity analyses exploring the validity of MR assumptions and the role of pleiotropy of other cardiometabolic risk factors. There was also evidence of higher glucose and glycated hemoglobin causing infertility in women, but the findings were imprecise and did not pass our P-value threshold for multiple testing. The results for lipids and blood pressure were close to the null, suggesting that these did not cause infertility.

LIMITATIONS, REASONS FOR CAUTION

We did not know if underlying causes of infertility were in the woman, man, or both. Our analyses only involved couples who had conceived. We did not have data on circulating levels of cardiometabolic risk factors, and we opted to conduct an MR analysis using GWAS summary statistics. No sex-specific genetic instruments on cardiometabolic risk factors were available. Our results may be affected by selection and misclassification bias. Finally, the characteristics of our study sample limit the generalizability of our results to populations of non-European ancestry.

WIDER IMPLICATIONS OF THE FINDINGS

Treatments for lower fasting insulin levels may reduce the risk of infertility in women.

STUDY FUNDING/COMPETING INTEREST(S)

The MoBa Cohort Study is supported by the Norwegian Ministry of Health and Care Services and the Norwegian Ministry of Education and Research. This work was supported by the European Research Council [grant numbers 947684, 101071773, 293574, 101021566], the Research Council of Norway [grant numbers 262700, 320656, 274611], the South-Eastern Norway Regional Health Authority [grant numbers 2020022, 2021045], and the British Heart Foundation [grant numbers CH/F/20/90003, AA/18/1/34219]. Open Access funding was provided by the Norwegian Institute of Public Health. The funders had no role in the study design; the collection, analysis, and interpretation of data; the writing of the report; or the decision to submit the article for publication. D.A.L. has received research support from National and International government and charitable bodies, Roche Diagnostics and Medtronic for research unrelated to the current work. O.A.A. has been a consultant to HealthLytix. The rest of the authors declare that no competing interests exist.

TRIAL REGISTRATION NUMBER

N/A.

Parental genetically predicted liability for coronary heart disease and risk of adverse pregnancy outcomes: a cohort study

BACKGROUND

Adverse pregnancy outcomes (APO) may unmask or exacerbate a woman's underlying risk for coronary heart disease (CHD). We estimated associations of maternal and paternal genetically predicted liability for CHD with lifelong risk of APOs. We hypothesized that associations would be found for women, but not their male partners (negative controls).

METHODS

We studied up to 83,969‬ women (and up to 55,568‬ male partners) from the Norwegian Mother, Father and Child Cohort Study or the Trøndelag Health Study with genotyping data and lifetime history of any APO in their pregnancies (1967-2019) in the Medical Birth Registry of Norway (miscarriage, stillbirth, hypertensive disorders of pregnancy, gestational diabetes, small for gestational age, large for gestational age, and spontaneous preterm birth). Maternal and paternal genetic risk scores (GRS) for CHD were generated using 148 gene variants (p-value < 5 × 10-8, not in linkage disequilibrium). Associations between GRS for CHD and each APO were determined using logistic regression, adjusting for genomic principal components, in each cohort separately, and combined using fixed effects meta-analysis.

RESULTS

One standard deviation higher GRS for CHD in women was related to increased risk of any hypertensive disorders of pregnancy (odds ratio [OR] 1.08, 95% confidence interval [CI] 1.05-1.10), pre-eclampsia (OR 1.08, 95% CI 1.05-1.11), and small for gestational age (OR 1.04, 95% CI 1.01-1.06). Imprecise associations with lower odds of large for gestational age (OR 0.98, 95% CI 0.96-1.00) and higher odds of stillbirth (OR 1.04, 95% CI 0.98-1.11) were suggested. These findings remained consistent after adjusting for number of total pregnancies and the male partners' GRS and restricting analyses to stable couples. Associations for other APOs were close to the null. There was weak evidence of an association of paternal genetically predicted liability for CHD with spontaneous preterm birth in female partners (OR 1.02, 95% CI 0.99-1.05), but not with other APOs.

CONCLUSIONS

Hypertensive disorders of pregnancy, small for gestational age, and stillbirth may unmask women with a genetically predicted propensity for CHD. The association of paternal genetically predicted CHD risk with spontaneous preterm birth in female partners needs further exploration.

Both reduced ovarian reserve and severe semen alterations are overrepresented in couples seeking assisted reproductive technology treatment for the first time: a cross-sectional study

BACKGROUND

Once a mate choice decision has been made, couples that fail to reach a live birth in natural and/or intrauterine insemination (IUI) cycles will likely visit fertility clinics seeking assisted reproductive technology (ART) treatment. During the more or less prolonged period of infertility experienced, those couples with mild/moderate reproductive anomalies would have advantage over couples displaying more severe reproductive alterations in achieving a natural or IUI conception. Thus, we can expect to find a progressive increase in the proportion of couples with more severe reproductive anomalies as duration of infertility rises. In this study, we aim to ascertain whether there is an association between male and female infertility diagnoses and duration of infertility in couples seeking ART treatment for the first time.

METHODS

A cross-sectional analysis of 1383 infertile couples that sought ART treatment for the first time. Forward-stepwise binary logistic regression analyses were applied to calculate exponentiated regression coefficients.

RESULTS

Men suffering from any combination of oligo-, astheno-, and teratozoospermia (ACOAT) exhibited higher odds of having a duration of infertility > 2 years compared with non-ACOAT men [odds ratio (95% confidence interval): 1.340 (1.030-1.744)]. Women from ACOAT couples displaying a duration of infertility > 2 years presented shorter menstrual cycles (P ≤ 0.047) and lower antral follicular count (AFC) values (P ≤ 0.008) and serum anti-Müllerian hormone (AMH) levels (P ≤ 0.007) than women from non-ACOAT couples exhibiting > 2 years of infertility. Likewise, AFC values (P ≤ 0.013) and serum AMH levels (P ≤ 0.001) were decreased when compared with women from ACOAT couples displaying ≤ 2 years of infertility. A relative low but significant percentage of ACOAT couples displaying > 2 years of infertility stood out for their smoking habits.

CONCLUSIONS

Couples consisting of ACOAT men and women with a relative low ovarian reserve are overrepresented in couples seeking ART treatment for the first time after experiencing > 2 years of infertility. This outcome leads us to develop a general hypothesis proposing that the origin of couple's infertility is a consequence of a process of positive assortative mating shaped by sexual selection forces.

Beyond body mass index: a synthesis of lifestyle factors that may influence in vitro fertilisation outcomes

There are several lifestyle factors that are thought to potentially impact in vitro fertilisation outcomes, including body mass index, smoking, alcohol consumption, caffeine, dietary patterns and physical activity. Eligibility criteria for in vitro fertilisation in England often require individuals to be non-smokers, drug free and have a body mass index <30kg/m2. Some researchers have questioned the scientific and ethical basis for the use of body mass index thresholds in fertility treatment, citing evidence that other factors may have a greater effect on the chance of success of in vitro fertilisation. This article aims to briefly synthesise the current evidence on how other factors such as smoking, alcohol, recreational drugs, smoking, caffeine, dietary patterns and physical activity may impact in vitro fertilisation outcomes.

The causal association between smoking initiation, alcohol and coffee consumption, and women's reproductive health: A two-sample Mendelian randomization analysis

Objective: A number of epidemiological studies have demonstrated that smoking initiation and alcohol and coffee consumption were closely related to women's reproductive health. However, there was still insufficient evidence supporting their direct causality effect. Methods: We utilized two-sample Mendelian randomization (TSMR) analysis with summary datasets from genome-wide association study (GWAS) to investigate the causal relationship between smoking initiation, alcohol and coffee consumption, and women's reproductive health-related traits. Exposure genetic instruments were used as variants significantly related to traits. The inverse-variance weighted (IVW) method was used as the main analysis approach, and we also performed MR-PRESSO, MR-Egger, weighted median, and weighted mode to supplement the sensitivity test. Then, the horizontal pleiotropy was detected by using MRE intercept and MR-PRESSO methods, and the heterogeneity was assessed using Cochran's Q statistics. Results: We found evidence that smoking women showed a significant inverse causal association with the sex hormone-binding globulin (SHBG) levels (corrected β = -0.033, p = 9.05E-06) and age at menopause (corrected β = -0.477, p = 6.60E-09) and a potential positive correlation with the total testosterone (TT) levels (corrected β = 0.033, p = 1.01E-02). In addition, there was suggestive evidence for the alcohol drinking effect on the elevated TT levels (corrected β = 0.117, p = 5.93E-03) and earlier age at menopause (corrected β = -0.502, p = 4.14E-02) among women, while coffee consumption might decrease the female SHBG levels (corrected β = -0.034, p = 1.33E-03). Conclusion: Our findings suggested that smoking in women significantly decreased their SHBG concentration, promoted earlier menopause, and possibly reduced the TT levels. Alcohol drinking had a potential effect on female higher TT levels and earlier menopause, while coffee consumption might lead to lower female SHBG levels.