Associations between health behaviours, fertility and reproductive outcomes: triangulation of evidence in the Norwegian Mother, Father and Child Cohort Study (MoBa)

A Systematic Review of Mendelian Randomization in Spontaneous Miscarriage

Spontaneous miscarriage (SM) is a common pregnancy complication. Although clinical factors are associated with SM, establishing causality is challenging. Mendelian randomization (MR) helps evaluate the causal effects of exposure variables. This study systematically reviewed 31 MR studies performed in SM, identifying causal relationships between SM and smoking, obesity, insomnia, rheumatoid arthritis, and immune-related factors. Smoking initiation and insomnia were identified as risk factors for SM. Coffee consumption showed no causal association with SM risk. Inconsistent evidence was reported for alcohol intake, BMI, depression, and RA regarding their causal relationships with SM. Smoking initiation, specific cytokines (eg, IL-12, TNF-β), and immune cells (eg, CD4+ T cells) demonstrated causal associations with the number of SM. Notably, key SNPs like rs13261666 and rs7127595 played significant roles in MR analyses due to their strong genetic associations with risk factors. Future research should further investigate the mechanistic pathways linking these genetic variants to SM, aiming to provide precise guidance for clinical prevention and treatment. Additionally, inconsistencies in MR results may stem from differences in data sources, SNP selection criteria, and statistical methodologies, indicating the importance of improving data consistency and standardizing analytical approaches in future research.

Exploring pleiotropy in Mendelian randomisation analyses: What are genetic variants associated with 'cigarette smoking initiation' really capturing?

Genetic variants used as instruments for exposures in Mendelian randomisation (MR) analyses may have horizontal pleiotropic effects (i.e., influence outcomes via pathways other than through the exposure), which can undermine the validity of results. We examined the extent of this using smoking behaviours as an example. We first ran a phenome-wide association study in UK Biobank, using a smoking initiation genetic instrument. From the most strongly associated phenotypes, we selected those we considered could either plausibly or not plausibly be caused by smoking. We examined associations between genetic instruments for smoking initiation, smoking heaviness and lifetime smoking and these phenotypes in UK Biobank and the Avon Longitudinal Study of Parents and Children (ALSPAC). We conducted negative control analyses among never smokers, including children. We found evidence that smoking-related genetic instruments were associated with phenotypes not plausibly caused by smoking in UK Biobank and (to a lesser extent) ALSPAC. We observed associations with phenotypes among never smokers. Our results demonstrate that smoking-related genetic risk scores are associated with unexpected phenotypes that are less plausibly downstream of smoking. This may reflect horizontal pleiotropy in these genetic risk scores, and we would encourage researchers to exercise caution this when using these and genetic risk scores for other complex behavioural exposures. We outline approaches that could be taken to consider this and overcome issues caused by potential horizontal pleiotropy, for example, in genetically informed causal inference analyses (e.g., MR) it is important to consider negative control outcomes and triangulation approaches, to avoid arriving at incorrect conclusions.

High Prevalence of Tobacco Consumption among Pregnant Women in a Southern European City (Seville): A Challenge for the Health System

The prevalence of prenatal tobacco exposure remains high in many countries, particularly in southern Europe. The aims of this study were to estimate the prevalence of smoking among pregnant women in a southern Spanish city (Seville) and to identify the associated sociodemographic and obstetric characteristics. In a descriptive, cross-sectional study, a random sample of pregnant women who were scheduled to undergo a morphology scan at their public referral hospital in their 20th week of gestation were interviewed in person. At the start of pregnancy, 38.2% of the pregnant women were smokers. In the twentieth week, 19.1% continued to smoke, and the same percentage had quit. The prevalence of smoking in pregnant women was higher among those with a low level of education (60% among pregnant women with no studies and 30.4% in those with primary education) and among those who had had abortions (38.5%). Pregnant smokers with obesity were the least likely to have given up smoking during pregnancy. Women with a lower educational level should be a prime target for cross-sectoral interventions aimed at preventing prenatal tobacco exposure. Implementation of support measures for providing effective clinical advice in preconception and prenatal care regarding healthy lifestyles is particularly needed.

Preconception and Early-Pregnancy Body Mass Index in Women and Men, Time to Pregnancy, and Risk of Miscarriage

Importance

Obesity in women is associated with reduced fertility and an increased risk of miscarriage. These associations might also be present across the full range of body mass index (BMI) categories as well as among men.

Objective

To investigate the associations of preconception BMI in both partners with time to pregnancy and miscarriage.

Design, Setting, and Participants

This population-based prospective cohort study was conducted in Rotterdam, the Netherlands, between August 9, 2017, and July 1, 2021. A total of 3604 women and their partners were included from the preconception period onward with follow-up until birth. The date of analysis was July 12, 2024.

Exposure

Body mass index (calculated as weight in kilograms divided by height in meters squared) measured in preconception or early pregnancy.

Main Outcome and Measures

Fecundability, defined as the probability of conceiving within 1 month; subfertility, defined as time to pregnancy or duration of actively pursuing pregnancy of more than 12 months or use of assisted reproductive technology; and miscarriage, defined as pregnancy loss before 22 weeks of gestation. These measures were assessed using questionnaires and via the obstetric caregiver.

Results

The study population for time-to-pregnancy analyses consisted of 3033 episodes among women (median age, 31.6 years [IQR, 29.2-34.5 years]; median BMI, 23.5 [IQR, 21.2-26.5]) and 2288 episodes among men (median age, 33.4 years [IQR, 30.5-36.8 years]; median BMI, 24.9 [IQR, 23.0-27.4]). The study population for miscarriage analyses consisted of 2770 pregnancy episodes among women (median age, 31.5 years [IQR, 28.9-34.3 years]; median BMI, 23.5 [IQR, 21.3-26.7]) and 2189 pregnancy episodes among men (median age, 33.5 years [IQR, 30.4-36.8 years]; median BMI, 25.0 [IQR, 23.0-27.5]). Higher BMI in women and men was associated with lower fecundability: for every unit increase in BMI, fecundability decreased (fecundability ratio [FR]: women, 0.98 [95% CI, 0.97-0.99]; men, 0.99 [95% CI, 0.98-1.00]). Women with overweight (FR, 0.88 [95% CI, 0.80-0.98]) and obesity (FR, 0.72 [95% CI, 0.63-0.82]) had lower fecundability compared with women with normal weight. Compared with normal weight in women, underweight (odds ratio [OR], 1.88 [95% CI, 1.22-2.88]), overweight (OR, 1.35 [95% CI, 1.11-1.63]), and obesity (OR, 1.67 [95% CI, 1.30-2.13]) were associated with increased odds of subfertility. In men, obesity was associated with increased odds of subfertility (OR, 1.69 [95% CI, 1.24-2.31]). Compared with normal weight in women, overweight (OR, 1.49 [95% CI, 1.12-1.98]) and obesity (OR, 1.44 [95% CI, 1.00-2.08]) were associated with increased odds of miscarriage.

Conclusions and Relevance

In this cohort study, BMI outside of the normal category in women and men during the preconception or early-pregnancy periods was associated with time to pregnancy and miscarriage. Optimizing BMI in women and men from the preconception period onward might be an important strategy to improve fertility outcomes.

Association of urinary metal element with semen quality: a cross-sectional study from Eastern China

The effect of metallic elements on semen quality remains controversial, with limited evidence on the effects of metal mixtures. We conducted a study involving 338 participants from multiple centers in Eastern China, measuring 17 urinary metals and semen quality parameters. Our analysis used various statistical models, including multivariate logistic and linear regression, Bayesian Kernel Machine Regression, and weighted quantile sum models, to examine the associations between metal levels and semen quality. Logistic regression showed that higher urinary lead was associated with increased risk of abnormal sperm concentration (OR = 1.86, p = 0.021), arsenic to higher abnormal progressive motility risk (OR = 1.49, p = 0.027), and antimony to greater abnormal total motility risk (OR = 1.37, p = 0.018). Conversely, tin was negatively correlated with the risk of abnormal progressive motility (OR = 0.76, p = 0.012) and total motility (OR = 0.74, p = 0.003), respectively. Moreover, the linear models showed an inverse association between barium and sperm count, even after adjusting for other metals (β = - 0.32, p < 0.001). Additionally, the WQS models showed that the metal mixture may increase the risk of abnormal total motility (βWQS = 0.55, p = 0.046). In conclusion, semen quality may be adversely affected by exposure to metals such as arsenic, barium, lead, and antimony. The combined effect of the metal mixture appears to be particularly impaired total motility.

Treatment With a Patented 3.6:1 Myo-Inositol to D-chiro-Inositol Ratio, Antioxidants, Vitamins and Minerals Food Supplement in Women With a History of Assisted Reproductive Technique (ART) Failures: A Series of Case Reports

Infertility affects 15% of couples in reproductive age worldwide. In women in particular, infertility can be caused by various abnormalities, with polycystic ovary syndrome (PCOS) being the most common. Currently, there are many assisted reproductive techniques (ART) available to combat the burden of infertility. However, positive results are not guaranteed. The administration of inositol has been shown to increase positive reproductive outcomes in women undergoing ART. Here we present a series of clinical cases in which women with a history of infertility and previously failed ART, supplemented with a specific 3.6:1 MYO:DCI ratio, antioxidants, vitamins, and minerals for a period of 1 to 3 months before undergoing in vitro fertilization (IVF). In this series of case reports, we provide preliminary evidence that supplementation with a specific 3.6:1 MYO to DCI ratio, as well as antioxidants, vitamins, and minerals may contribute positively to female fertility in women undergoing IVF, with a history of primary or secondary infertility and previously failed ART.

Identifying causal associations between women's reproductive traits and risk of schizophrenia: a multivariate validated two-sample Mendelian randomization analysis

BACKGROUND

A significant association between women's reproductive traits and the risk of schizophrenia (SCZ) has been discovered, but the causalities remain unclear. We designed a two-sample univariate Mendelian randomization (MR) study using female-specific SNPs collected from a large-scale genome-wide association study as a genetic tool to explore the causal effect of female reproductive traits on the risk of SCZ, and conducted a multivariate MR study to re-validate the above findings.

METHODS

From extensive genome-wide association studies (GWAS) of people with European ancestry (n = 176,881 to 418,758 individuals), summary-level data on five female reproductive variables were extracted. Summary-level information on SCZ was taken from a GWAS meta-analysis involving 320,404 people with European ancestry. The inverse variance weighting estimations for both univariable MR (UVMR) and multivariable MR (MVMR) were presented as the primary results. MR-Egger, weighted median, simple mode, and weighted mode regression methods for UVMR, and MVMR-Egger, MVMR-Lasso, and MVMR-median methods for MVMR were used for sensitivity analyses.

RESULTS

The UVMR produced compelling proof for a connection between genetically predicted later age at first sexual intercourse (AFS) (OR, 0.632; 95% CI, 0.512-0.777; P < 0.01) and decreased SCZ risk. Pleiotropy analysis of the AFS-SCZ association confirmed the robustness of the MR results (P > 0.05). Consistent, substantial causal effects of AFS (OR, 0.592; 95%CI, 0.407-0.862; P < 0.01) on the risk of SCZ were demonstrated after adjusting for body mass index, years of schooling, and smoking initiation using MVMR.

CONCLUSIONS

Our findings provide convincing evidence that early AFS is a risk factor for SCZ. SCZ risk may be decreased by raising awareness of reproductive healthcare for women.

Maternal thyroid peroxidase antibody positivity and its association with incidence of low birth weight in infants

Background

Autoimmune thyroid disease is a prevalent condition affecting women of reproductive age, leading to thyroid dysfunction and impacting pregnancy outcomes. While the critical role of thyroid hormone in pregnancy outcomes is well-established, the potential association between positive anti-thyroid peroxidase antibodies (TPOAb) and adverse pregnancy outcomes in pregnant women with normal thyroid function remains unclear.

Objective

This study aims to investigate the relationship between maternal TPOAb positivity and adverse pregnancy outcomes with normal thyroid function.

Methods

We collected baseline information from pregnant women who visited our hospital between February 2009 and June 2012. Blood samples were taken to measure thyroid stimulating hormone (TSH), free thyroxine (FT4), TPOAb, and anti-thyroglobulin antibodies (TGAb). The incidence of adverse pregnancy outcomes was compared between TPOAb-positive and TPOAb-negative groups among participants with normal thyroid function.

Results

A total of 7,046 pregnant women with normal thyroid function were included, comprising 6,700 with negative TPOAb and 346 with positive TPOAb. The TPOAb-positive group exhibited a higher age (26.0 vs. 27.0 years, p = 0.02) and greater serum TSH levels (1.72 vs. 1.94 mIU/L, p = 0.029), while the gestational week of blood collection was lower (31.9 vs. 26.5 weeks, p = 0.001). Univariate analysis revealed a higher incidence of low birth weight (LBW) in offspring of TPOAb-positive women compared to the TPOAb-negative group (3.5% vs. 1.9%, p = 0.035). After adjusting for confounding factors such as age, gestational week of blood collection, menstrual history, education level, gestational diabetes, gestational hypertension, TGAb, TSH, and FT4, TPOAb positivity emerged as an independent risk factor for LBW infants (OR: 2.317, 95% CI: 1.057-5.076, p = 0.036), while other adverse pregnancy outcomes did not show a significant correlation with TPOAb positivity.

Conclusion

Our findings suggest that TPOAb-positive pregnant women with normal thyroid function are more likely to deliver LBW infants. Regular monitoring of TPOAb-positive pregnancies and timely interventions throughout all stages of pregnancy are crucial.