Paternal Exposure to Non-essential Heavy Metal Affects Embryo Cleavage and Implantation in Intracytoplasmic Sperm Injection (ICSI) Cycles: Evidence for a Paradoxical Effect

Paternal Lead Exposure and Pregnancy Outcomes: A Systematic Review and Meta-Analysis

Paternal lead exposure has emerged as a potential contributor to adverse pregnancy outcomes, yet its impact remains underexplored compared to maternal exposure. This systematic review and meta-analysis synthesize evidence on the association between paternal lead exposure and pregnancy outcomes to inform public health interventions and future research. To evaluate the association between paternal lead exposure and adverse pregnancy outcomes, including spontaneous abortion, low birth weight, preterm birth, small-for-gestational-age, and congenital anomalies. A systematic search of PubMed, Scopus, and Google Scholar was conducted up to August 2024. Observational studies examining paternal lead exposure (⩾15 µg/dL) and its effects on pregnancy outcomes were included. Data synthesis adhered to PRISMA 2020 guidelines, and study quality was assessed using the Newcastle-Ottawa Scale. Meta-analysis was performed using a random-effects model to compute pooled odds ratios (ORs) with 95% confidence intervals (CIs). Eleven studies were included in the systematic review, with 7 contributing to the meta-analysis. The pooled OR for congenital anomalies associated with paternal lead exposure was statistically significant (OR = 2.09, 95% CI: 2.09-3.35; P < .01), indicating a strong association. However, no significant associations were observed for other outcomes: spontaneous abortion (OR = 1.11, 95% CI: 0.75-1.64), low birth weight (OR = 0.98, 95% CI: 0.68-1.39), preterm birth (OR = 1.57, 95% CI: 0.61-4.05), and small-for-gestational-age infants (OR = 0.92, 95% CI: 0.78-1.09). Heterogeneity was low for most outcomes, except for spontaneous abortion (I 2 = 39%) and preterm birth (I 2 = 52%). This study highlights a significant association between paternal lead exposure and congenital anomalies, emphasizing the need for occupational and environmental regulations targeting lead exposure among men of reproductive age.

Mercury, natural fertility and outcomes of assisted reproduction: A systematic review

The primary route of mercury exposure for the general population is through consumption of contaminated seafood. There is a biological basis for an adverse effect of mercury exposure on human fertility. The goal of this review was to evaluate the existing literature on the association between mercury and pregnancy, among men and women attempting to conceive with and without assisted reproductive technology (ART). Systematic searches were performed in PubMed, EMBASE, Scopus and Web of Science for papers published up to March 2023 with no early date restriction, only including studies with a biomarker measurement of mercury exposure. We identified 11 studies examining mercury and natural fertility and 12 studies examining mercury and outcomes of assisted reproduction (implantation or clinical pregnancy). The accumulated evidence provides some support for a null association between bodily mercury concentrations and natural fertility among women, however, a large proportion of studies did not report adjusted estimates or were extremely imprecise. The majority of studies of natural fertility were also cross-sectional in nature. There was no evidence for an inverse or null association between mercury and natural fertility among men, or mercury and ART outcomes among men or women. In spite of biological plausibility, the existing evidence includes studies that are imprecise and often conflicting and does not allow us to make definitive conclusions on the associations of mercury exposure with successful pregnancy. Additional, larger studies are warranted, especially among individuals with high concentrations of mercury exposure as these individuals may be underrepresented in the current literature.

Influence of Seminal Metals on Assisted Reproduction Outcome

Increased levels of metal ions in human seminal fluid have a significant correlation with male fertility. Few publications explain the effect of metals in semen and their influence on assisted reproductive treatments. Semen parameters and the levels of twenty-two metals were measured in the seminal fluid of 102 men attended in a Reproductive Unit. Metals were determined by optical emission spectrophotometry. A statistical relationship was found between spermiogram and iron, which was lower than expected in pathological spermiograms (p = 0.032); zinc (p = 0.066), calcium (p = 0.047), and magnesium (p = 0.048) mean levels were higher in normozoospermics. More days of sexual abstinence correlates with higher seminal zinc (p = 0.001) and magnesium levels (p = 0.002). Lower vanadium values were found to be associated with higher fertilization rates (p = 0.039). Higher values of lead (p = 0.052) and vanadium (p = 0.032) were obtained in patients who did not reach 100% embryo cleavage rate. Aluminium (p = 0.042) and sodium (p = 0.002) were found in lower amounts associated with better blastocyst rates. The implantation rate shows an inverse association with women's age and iron and calcium content, compared to magnesium and sodium which presented a significant direct association with this percentage. A significant direct relationship was found between the positive evolution of pregnancy and the values of zinc (p = 0.004), calcium (p = 0.013), potassium (p = 0.002), and magnesium (p = 0.009). The study confirms that zinc, iron, calcium, sodium, aluminium, magnesium, vanadium, and lead have positive-negative effects on reproduction and support the analysis of metals in semen as a new line of study on male fertility with implications for reproductive outcomes.