IVF News

Researchers at Baylor College of Medicine have successfully restored fertility in a mouse model of non-obstructive azoospermia (NOA), a form of male infertility in which sperm production fails despite unobstructed reproductive ducts. The work, published in Proceedings of the National Academy of Sciences (PNAS), presents a promising step toward the development of therapeutic approaches that could help men with this currently untreatable condition.

Non-obstructive azoospermia affects roughly one percent of men and is one of the most severe forms of infertility. In these cases, the testes are unable to produce mature sperm, often due to genetic mutations that disrupt spermatogenesis. Conventional treatments such as hormone therapy or surgery offer little benefit, leaving assisted reproductive technologies as the only potential route to conception—often relying on donor sperm rather than the patient’s own.

The Baylor research team focused on a key gene, Tex14, which is essential for forming intercellular bridges between developing germ cells. These bridges are critical for coordinating sperm development. In mice lacking Tex14, the germ cells fail to progress beyond early stages, resulting in azoospermia. Using a novel lipid nanoparticle-based mRNA therapy, researchers delivered a functional Tex14 transcript directly into the testes. Remarkably, the treated mice began producing functional sperm capable of fertilizing eggs and producing healthy offspring.

This study highlights how mRNA therapy, best known for its role in vaccines, can be repurposed to temporarily restore missing or defective proteins within the testes. Because the approach does not alter the genome, it may offer a reversible and safer alternative to permanent gene editing. It also opens a path for treating a range of genetic causes of male infertility, particularly those where a single gene defect disrupts sperm development.

Beyond Tex14, the researchers believe this platform could be adapted for other testicular genes and eventually refined for human use. Translating this therapy from mice to men will require addressing delivery challenges, dosage control, and immune responses, but the proof of concept demonstrates a powerful new tool in reproductive medicine.

The findings suggest that male infertility—often regarded as irreversible when due to genetic defects—may one day be treatable through targeted molecular replacement rather than invasive procedures or donor gametes.

Sources

13 October 2025, Proceedings of the National Academies of Science

Sperm and offspring production in a nonobstructive azoospermia mouse model via testicular mRNA delivery using lipid nanoparticles

14 October 2025, Baylor College of Medicine

Researchers restore fertility in mouse model of non-obstructive azoospermia

17 October 2025, Drug Target Review

New mRNA therapy could inform future male infertility treatments

Sperm cells must undergo a remarkable transformation to reach and fertilize an egg. In a new study published in Proceedings of the National Academy of Sciences (PNAS), researchers at Michigan State University have identified a key molecular mechanism that enables sperm to achieve “overdrive” motion, a rapid and forceful swimming pattern known as hyperactivation. This discovery sheds light on the finely tuned processes that determine male fertility and could provide new avenues for treating infertility or developing non-hormonal contraceptives.

The study focuses on CatSper, a calcium ion channel located in the sperm tail that controls how calcium ions enter the cell. These ions trigger the whip-like movements required for sperm to navigate the female reproductive tract and penetrate the egg’s protective layers. The MSU team used advanced molecular and imaging techniques to show how CatSper transitions from a basal to a hyperactivated state, allowing sperm to dramatically increase their motility at the crucial moment before fertilization.

This “overdrive” mode is essential for sperm to overcome physical barriers such as cervical mucus and the zona pellucida surrounding the oocyte. The researchers found that specific chemical signals within the female reproductive tract stimulate the CatSper channel, changing its structure and activity. These modifications effectively act as a molecular switch that shifts sperm from steady swimming to the powerful thrusts needed for fertilization.

Understanding this process at the molecular level provides new insight into why certain genetic mutations in CatSper lead to male infertility. It also opens possibilities for designing drugs that can either enhance or inhibit this signaling pathway. Enhancing CatSper activity could help couples struggling with fertilization failure, while targeted inhibitors could serve as a reversible, non-hormonal form of contraception that prevents sperm from reaching hyperactivation.

This work not only deepens our understanding of reproductive biology but also demonstrates how precise molecular mechanisms underlie the seemingly simple behavior of sperm motility. By revealing how sperm achieve overdrive, scientists are one step closer to harnessing or regulating this process for clinical benefit.

Sources

28 October 2025. Michigan State University News

Fuel for the finish line: How sperm achieve 'overdrive'

28 October 2025. Proceedings of the National Academy of Sciences (PNAS)

Sperm meet the elevated energy demands to attain fertilisation competence by increasing flux through aldolase

A recent study by researchers at the Wellcome Sanger Institute and their collaborators has uncovered how sperm evolve within the human body as men age, leading to an accumulation of harmful genetic mutations that may raise disease risk in their children. Published in Nature (October 2025), the research provides a new understanding of how so-called “selfish” sperm cells gain an advantage, multiplying over time while carrying mutations that can disrupt normal development.

Human sperm are produced continuously throughout life, giving rise to billions of cells from a pool of stem cells within the testes. Each division of these cells introduces small errors in DNA, and over decades of sperm production, mutations accumulate. The study reveals that certain mutations give sperm-producing stem cells a competitive edge, allowing them to expand at the expense of normal cells. This evolutionary process means that as men age, their sperm population becomes dominated by these “selfish” lineages, increasing the likelihood of passing on disease-related mutations to offspring.

Using single-cell genetic sequencing, the team analyzed testicular tissue to map how these mutated cells evolve and spread. The findings show clear patterns of clonal expansion—small pockets of sperm-producing stem cells carrying identical mutations—indicating that natural selection is occurring at the cellular level. Many of these mutations affect genes involved in cell signaling and development, including those linked to conditions such as achondroplasia, Apert syndrome, and potentially autism spectrum disorders.

This research highlights an underappreciated aspect of reproductive biology: that natural selection operates not only at the organismal level but also within individual tissues. As men age, this internal competition reshapes the genetic landscape of their sperm, increasing both diversity and the potential for transmitting harmful variants.

The findings may influence future fertility counseling and genetic screening strategies, helping clinicians better understand age-related reproductive risks. Researchers are now exploring whether interventions could one day slow or counteract this selfish evolution, protecting sperm integrity as men age.

Sources

28 October 2025. Wellcome Sanger Institute

Hidden evolution in sperm raises disease risk for children as men age

28 October 2025. Nature

Sperm sequencing reveals extensive positive selection in the male germline

28 October 2025. New Scientist

Selfish sperm see older fathers pass on more disease-causing mutations

The longstanding narrative that ovarian aging is driven mainly by declining egg number and quality is being reframed by new work that maps the entire cellular ecosystem of the ovary across age in mice and humans. Using whole-organ 3D imaging combined with single-cell and spatial transcriptomics, researchers show that how eggs mature, persist, and respond to stimulation depends on the surrounding microenvironment, including stromal cells, extracellular matrix, vasculature, immune components, and previously underappreciated neural elements. The analysis, published in Science on October 9, 2025, provides a reference atlas for reproductive aging and connects ovarian biology to systemic health after menopause. 

Whole-organ optical clearing and light-sheet imaging revealed striking spatial organization. In human ovaries, oocytes are not evenly distributed but cluster in discrete pockets separated by egg-sparse zones. With age, these pockets thin and the density of both resting and growing follicles falls. Equivalent age windows in mice show parallel declines in follicle reserves and IVF success, aligning model and human observations. These spatial findings, which are not apparent in conventional section-based histology, set a new baseline for interpreting follicle counts and stimulation responses in clinical and preclinical contexts. 

The atlas resolves 11 major ovarian cell classes and charts their age-related transcriptional shifts. Among non-germline compartments, fibroblasts, smooth muscle, and epithelial cells exhibit prominent remodeling signatures with age, suggesting that matrix turnover, contractility, and barrier functions collectively condition follicle fate. These insights point to testable interventions that target stroma and extracellular matrix dynamics, for example anti-fibrotic strategies to preserve tissue pliability and follicle access to nutrients and paracrine signals. 

A notable advance is the delineation of the ovarian nervous system. The atlas documents dense sympathetic nerve networks intertwined with follicles, supported by local glia. Functional perturbation in mice lacking sympathetic innervation produced fewer growing follicles and accumulation of immature follicles, implicating neural signaling in coordinating maturation cycles. This neural dimension integrates with clinical observations in disorders like PCOS and raises the prospect that neuromodulatory or neuroimmune pathways could be leveraged to optimize folliculogenesis. 

For IVF practice, several translational implications follow. First, spatial heterogeneity means that biopsy location and sectioning strategy can bias follicle metrics, arguing for standardized sampling or volumetric imaging when feasible. Second, stimulation protocols may benefit from considering stromal state and innervation rather than focusing solely on gonadotropin dosing. Third, age-linked matrix and vascular changes may alter drug penetration and oxygenation within the cortex, influencing oocyte competence even when follicle counts appear reassuring. Together, these points motivate pairing ovarian reserve measures with markers of stromal integrity and neural tone to refine prognosis and personalize stimulation. 

The work also strengthens the translational bridge between mouse and human ovaries. By aligning shared and species-specific hallmarks across age, the atlas clarifies where mouse interventions are most likely to predict human benefit. It offers a scaffold for evaluating therapies that aim to slow ovarian aging, including matrix-targeted compounds, anti-inflammatory regimens, and approaches that preserve or recalibrate sympathetic inputs. As media coverage has emphasized, the ovary functions as a coordinated ecosystem. Intervening at that systems level may extend reproductive span while improving general health trajectories tied to the menopausal transition. 

Looking ahead, incorporating these ecosystem metrics into clinical studies could refine embryo selection and cumulative live birth predictions by connecting follicle geography and stromal state to oocyte quality and response. The field now has a shared reference to test whether modifying tissue mechanics, fibrosis, or neural signaling can measurably shift outcomes in controlled ovarian stimulation, oocyte cryopreservation, and fertility preservation after gonadotoxic exposures. 

Sources

9 October 2025. Science

Comparative analysis of human and mouse ovaries across age

9 October 2025. UCSF News

Why Does Female Fertility Decline So Fast? The Key Is the Ovary

9 October 2025. The Scientist

A Cellular Atlas of the Aging Ovary Reveals How Fertility Fades

9 October 2025. New Scientist

Hidden ecosystem of the ovaries plays a surprising role in fertility

Training Batch Schedule December 2025 

Batch  XII:    15th to 29th December

The International School of Embryology a unit of Chennai Fertility Centre and Research Institute was established to offer training in Advanced Reproductive Techniques and Embryology for clinicians and embryologists. It will help them to know in-depth knowledge and have good hands-on training. The members of our teaching faculty aim to bring Clinician and Embryologists to the highest level of knowledge about Assisted Reproductive Technology and practical capability.

Our courses cover basics in Andrology, Embryology, ICSI & Cryosciences (Hands-on).

Limited Seats. For admission Contact  9003111598 / 8428278218 

Training Batch Schedule November & December 2025 

Batch - XI & XII:    10th  to 24th  November & 15th to 29th December

The International School of Embryology a unit of Chennai Fertility Centre and Research Institute was established to offer training in Advanced Reproductive Techniques and Embryology for clinicians and embryologists. It will help them to know in-depth knowledge and have good hands-on training. The members of our teaching faculty aim to bring Clinician and Embryologists to the highest level of knowledge about Assisted Reproductive Technology and practical capability.

Our courses cover basics in Andrology, Embryology, ICSI & Cryosciences (Hands-on).

Limited Seats. For admission Contact  9003111598 / 8428278218 

For millions of people worldwide, the dream of having a genetically related child is halted by the absence of functional gametes, often due to advanced maternal age, disease, or medical treatment. Traditional in vitro fertilization (IVF) is simply ineffective for these patients.

But what if almost any cell in the body could be used as the starting point for life?

Researchers at Oregon Health and Science University (OHSU) have achieved a significant scientific milestone: creating early-stage human embryos by taking DNA from adult skin cells (fibroblasts) and fertilizing it with sperm. This proof-of-concept study, leveraging an innovative new cell division process, represents a "significant breakthrough in halving the human genome," according to experts.

From Skin Cell to Egg: Introducing Mitomeiosis

This new path to fertility relies on Somatic Cell Nuclear Transfer (SCNT), the same technique famously used to clone Dolly the Sheep.

In SCNT, the nucleus (containing the full set of 46 chromosomes) is removed from a donor skin cell and placed into a mature donor egg that has been stripped of its own genetic material.

The critical challenge is this: while standard body cells (like skin cells) carry 46 chromosomes (diploid), eggs and sperm must be haploid, carrying only 23 chromosomes each, so that when they combine, the resulting embryo has the correct total of 46.

The OHSU team successfully compelled the 46 chromosomes from the skin cell to discard half of their contents in a novel process they call mitomeiosis—a fusion of mitosis (standard cell division) and meiosis (gamete division). Senior author Prof. Shoukhrat Mitalipov noted, "Nature gave us two methods of cell division, and we just developed a third".

The residual metaphase activity within the enucleated MII (Metaphase II) oocyte cytoplasm forced the non-replicated somatic cell genomes (2n2c) to condense prematurely and form a metaphase-like spindle, bypassing the natural S-phase checkpoint.

Overcoming the Activation Stall

While SCNT successfully induced premature metaphase, initial attempts to fertilize the SCNT oocytes with sperm stalled; the chromosomes lined up but failed to finish separating, resulting in persistent MII arrest.

To circumvent this activation failure, researchers employed supplemental activation. They injected sperm via ICSI (Intracytoplasmic Sperm Injection) and then used electrical pulses to simulate the natural calcium signal required for activation, followed by incubation with roscovitine (a selective cyclin-dependent kinase inhibitor).

This combined approach successfully rescued the fertilization attempt. The mean somatic chromosome count retained within the zygotic pronuclei was 22.8 $\pm$ 1. This outcome conclusively demonstrated the feasibility of experimentally halving the diploid chromosome content.

Ultimately, 8.8% $\pm$ 5.2 (or about 9%) of the fertilized SCNT eggs developed to the blastocyst stage—the ball of cells typically transferred during clinical IVF. However, none were cultured beyond six days post-fertilization.

The Genomic Stability Hurdle

Despite the excitement surrounding the successful ploidy reduction, the resulting embryos faced major genetic defects.

Comprehensive chromosome tracing showed that unlike natural meiosis, which precisely pairs and separates chromosomes, segregation during mitomeiosis was random. The distribution of somatic homologs statistically resembled a Monte Carlo simulation calculated for random segregation. This random allocation resulted in severe chromosomal abnormalities, meaning the resulting embryos were aneuploid (carrying the wrong number or combination of chromosomes).

Furthermore, analysis confirmed the absence of crossover recombination between homologous chromosomes. Crossover is vital for creating the genetic diversity inherent to natural gametes.

As co-author Prof. Paula Amato explained, this random segregation means that most, if not all, of the resulting embryos had chromosomal abnormalities, such as too many or too few chromosomes, or improper combinations. These outcomes "would not be expected to result in a healthy baby".

Immature Potential: Why This Matters for Fertility

If perfected, this technology holds immense potential for reproductive medicine.

1. Addressing Infertility: It offers hope for women whose fertility has declined due to advanced age or medical treatments like chemotherapy, as it allows them to potentially use their own genetic material.
2. Enabling Same-Sex Reproduction: Critically, the somatic cells used for SCNT do not necessarily have to come from a woman; they could also use skin cells from a male. This opens the door for same-sex couples to have children genetically related to both partners.

However, the consensus among experts, including the lead researchers, is strong: this approach is "currently far too immature for clinical application". Prof. Mitalipov acknowledged that the criticisms regarding inefficiency and risk are fair, stating, "The bottom line is that we’re kind of halfway there, but still not exactly where we need to be".

Overcoming the mechanistic hurdles—particularly achieving accurate, non-random chromosome segregation and introducing recombination—is expected to require at least a decade of additional research to ensure efficacy and safety.

For years, we've operated under the widely accepted hypothesis that male subfertility is often driven by oxidative stress—that damaging imbalance between reactive oxygen species (ROS) and the body's natural antioxidant defenses. This theory fueled a massive market of over-the-counter supplements, marketed directly to patients as a non-invasive solution to "boost" semen quality.

But what happens when the most rigorous, large-scale evidence available challenges this entire approach?

The landmark SUMMER (Supplement Male Fertility) Randomized Clinical Trial (RCT), recently published in JAMA Network Open, provides definitive answers. And the message for fertility specialists and embryologists is clear: we need to stop recommending these supplements.

The Trial: A Look Under the Hood

The SUMMER trial was a gold-standard, multicenter, double-blind, placebo-controlled study conducted across 21 centers in the Netherlands. It enrolled 1,171 men seeking fertility care, whose partners were undergoing treatments ranging from expectant management (EM) to IUI, IVF, or ICSI.

What Was Tested?

The men were randomized to receive either a placebo or a specific, combined antioxidant supplement (Impryl) daily for six months. The tested supplement contained a cocktail of nutrients, including:

• Betaine (200 mg)
• L-cystine (200 mg)
• Niacin (16 mg)
• Zinc (10 mg)
• Folic acid (400 µg)
• Vitamins B6, B2, and B12

The primary goal was straightforward: to see if the supplement improved the rate of ongoing pregnancy (viable pregnancy at 12 weeks gestation) within six months.

The Unexpected Result: No Benefit, Possible Harm

The headline finding couldn't be clearer: The antioxidant supplement did not improve ongoing pregnancy ratescompared with the placebo.

Overall, the ongoing pregnancy rate within six months was 33.8% in the supplement group, compared to 37.5% in the placebo group—a non-significant difference.

The Critical 4–6 Month Window

However, the analysis of the secondary outcomes unveiled a far more concerning signal. Researchers focused on the optimal treatment effect window—between 4 and 6 months after randomization—a time frame chosen to account for the approximate 72-day cycle of spermatogenesis.

In this critical window, the ongoing pregnancy rate was significantly lower in the antioxidant supplement group (15.5%) compared with the placebo group (21.5%) (P = .02). This alarming finding suggests a potential adverse effect from the routine use of this antioxidant combination.

Direct Impact on ART Outcomes

For those of us working directly in the IVF/ICSI lab, the findings specific to assisted reproductive technology (ART) cycles are paramount:

1. Fresh Cycles Took a Hit: Pregnancy rates were significantly lower in the antioxidant supplement group for couples undergoing IVF or ICSI after ovum pickup (OPU) and after fresh embryo transfer (ET).
2. Frozen Cycles Were Spared: Interestingly, pregnancy rates after frozen-thawed ET showed no significant difference between the groups.
3. Embryo Metrics were Neutral: Crucially, lab metrics, such as fertilization rate (0.68 supplement vs. 0.64 placebo) and embryo utilization rate (0.50 supplement vs. 0.48 placebo), showed no significant differences. This indicates the supplement's negative effect may be related to sperm function in vivo or during fresh handling, rather than dramatically altering overall fertilization competence.

What About the Sperm?

The primary theory supporting these supplements—improving sperm health—did not hold up:

• No Benefit to Conventional Parameters: The supplement failed to produce significant differences in semen volume, sperm concentration, progressive motility, or total motile sperm count (TMSC) after 3–6 months.
• No DNA Repair: There were no significant differences in sperm DNA fragmentation (SDF) compared to the placebo group.
• Vitality Decreased: Alarmingly, the median sperm vitality was significantly lower in the antioxidant group after treatment compared with its own baseline value (dropping from 62.7% to 54.9%).

The Clinical Takeaway: Focus on What Works

The strength of the SUMMER trial, being a large-scale, well-controlled RCT, provides the strongest evidence to dateagainst the effectiveness of these popular combined antioxidant supplements.

The researchers emphasize that standard fertility treatments—IUI, IVF, and ICSI—remain the main evidence-based options for couples seeking to conceive.

The potential mechanism for the observed decrease in pregnancy rates may be reductive stress—the opposite of oxidative stress—where an excess of antioxidants shifts the redox balance in a way that is also harmful to sperm function. Given the general population of subfertile men may not have high oxidative stress to begin with (supported by the low baseline SDF in the trial subgroup), introducing high levels of antioxidants may tip the scale toward harm.

In summary: Routine use of antioxidant supplements in men seeking fertility care is not supported by the evidence and may potentially decrease pregnancy chances, particularly in fresh ART cycles.

The traditional view that inheritance is governed solely by DNA sequences has been increasingly challenged in recent decades. Embryologists must now integrate the crucial role of epigenetic inheritance—the transmission of biological traits via chemical modifications to DNA and associated proteins—into their understanding of early development. These modifications do not alter the underlying genetic code but instead influence how genes are switched on or off, often in response to external factors like stress, diet, or drug exposure.

While the concept of maternal epigenetic inheritance is relatively intuitive due to the direct biological connection during gestation, recent research confirms that fathers can also transmit environmentally induced epigenetic changes to their offspring. A novel collaborative study from EMBL Rome scientists, published in the EMBO Journal, reveals that a father’s preconception environment can leave subtle, yet detectable, molecular footprints in embryos, capable of shaping development and long-term health.

Experimental Design: Isolating Paternal Effects

To systematically examine how specific paternal environments influence early embryonic development, the research groups led by Ana Boskovic and Jamie Hackett conducted a collaborative study using mice under strictly controlled genetic and environmental conditions.

To induce environmental perturbations, prospective fathers were exposed to two distinct stressors:

1. Non-absorbable antibiotics (to disrupt the gut microbiota).
2. A low-protein, high-sugar diet (to alter nutrition).

To minimize experimental variability and isolate paternal effects, the analyses were performed on embryos resulting from in vitro fertilization (IVF). Embryos were collected approximately four days after fertilization, at the blastocyst stage, and individually analyzed to measure gene expression differences compared to controls (blastocysts from untreated fathers).

Key Findings on Early Embryogenesis

The study demonstrated that paternal environments before conception can influence offspring development at the earliest stages of embryogenesis. Both environmental perturbations led to significant changes in embryonic gene expression:

• Disrupted Gut Microbiota: An imbalanced paternal gut microbiome was shown to compromise the expression of key genes involved in extra-embryonic tissue development or growth.
• Altered Diet: Changes in the paternal diet (low-protein, high-sugar) were associated with a modest developmental delay.

Modulating Factors: Genetics and Paternal Age

Crucially, the study emphasized that inheritance involves a complex interaction between genetics and environmental influences. When scientists repeated the experiments using a different mouse strain, the outcome differed, suggesting that the genetic background modulates these effects and is a necessary consideration when assessing how environmental exposures impact offspring.

Furthermore, paternal age was identified as another important factor in epigenetic inheritance. Embryos derived from older fathers exhibited a stronger effect on gene expression, particularly affecting genes involved in immune-related processes.

Implications for Intergenerational Studies

This research represents a significant step toward understanding the mechanism of epigenetic inheritance through the paternal line. The investigators emphasized that large-scale experiments are essential to untangle how specific environmental factors contribute to epigenetic inheritance across different genetic backgrounds.

This tightly controlled experimental design serves as a template for future intergenerational studies aimed at understanding the impact of the environment on human disease risk. By applying additional tools to investigate early changes in offspring in response to paternal environments, the hope is to eventually pave the way for new strategies in disease prevention.

Sources

30 September 2025. European Molecular Biology Laboratory Rome

• Fathers shape embryonic development through molecular 'signatures'

26 September 2025. The EMBO Journal

• Embryonic signatures of intergenerational epigenetic inheritance across paternal environments and genetic backgrounds

Cannabis is one of the most widely used recreational drugs among people of reproductive age globally. Driven by rising legalization and easier access, cannabis use is increasing worldwide, often at higher strengths, with THC (tetrahydrocannabinol) potency rising from approximately 3% in the 1980s to around 15% or even 30% today.

While the effects of THC—the primary psychoactive compound—on male fertility (sperm count, motility, and DNA) and pregnancy outcomes are relatively well-documented, the impact on the female gamete, the oocyte (egg), has remained a significant knowledge gap. Oocytes are finite in number and highly sensitive to environmental factors, meaning any disruptions in their development could profoundly affect fertility and the health of future embryos.

Recent groundbreaking research, combining clinical analysis with controlled laboratory experiments, sheds light on this critical issue, revealing a complex, two-sided impact of THC on human egg quality.

The Dual Impact: Accelerated Maturation at a Genetic Cost

Researchers at the CReATe Fertility Centre in Toronto investigated how THC exposure influences human oocytes. The study used a dual approach: a retrospective analysis of patients undergoing in vitro fertilization (IVF) and controlled in vitro lab experiments.

1. The Retrospective Clinical Analysis

The team analyzed 1,059 follicular fluid samples from IVF patients, finding that approximately 6% (62 samples) tested positive for THC metabolites. Notably, 73% of those patients who tested positive had not reported cannabis use on their intake questionnaires, highlighting the potential issue of under-reporting in clinical settings.

The analysis revealed a key paradox:

• Increased Maturation: Concentrations of THC and its metabolites in the follicular fluid were positively correlated with a higher rate of oocyte maturation.
• Reduced Quality: However, the embryos that developed from these oocytes were significantly less likely to have the correct number of chromosomes (meaning a lower rate of euploid embryos) compared to matched controls.

This suggests that THC exposure may push oocytes to mature faster, but this comes "at the cost of genetic stability". A higher maturation rate may appear positive, but developing too quickly can disrupt the essential time chromosomes need to align perfectly for reproduction.

2. The In Vitro Mechanisms

To understand the biological basis for these clinical findings, researchers exposed immature oocytes donated by 24 patients to two concentrations of THC—a physiologically relevant dose (THC1) and a higher, supraphysiological dose (THC2).

Exposure to THC induced several harmful cellular and genetic changes:

• Chromosome Errors (Aneuploidy): Both THC concentrations led to a 9% increase in aneuploidy rates (embryos with an incorrect number of chromosomes) in the oocytes tested, along with a higher proportion of complex aneuploidies.
• Spindle Disruption: THC exposure resulted in a dose-dependent decrease in the proportion of oocytes with normal spindle morphology. Spindle structures are cellular machinery made of microtubules crucial for separating chromosomes during cell division, and abnormal spindles can lead to errors in chromosome number.
• Gene Expression Changes: THC altered gene activity within the oocytes. Many of the affected genes are critical for egg quality and embryo development, playing roles in inflammation, the extracellular matrix, and chromosome segregation. For instance, genes involved in GPCR signaling (RGS5 and RGS18) and inflammation (IFNG and IL33) were dysregulated. Furthermore, the downregulation of MMP9—a gene crucial for the breakdown of the extracellular matrix—may negatively affect key reproductive processes like ovulation, embryo development, and implantation.

The prevailing scientific hypothesis suggests that THC binds to cannabinoid receptors (CB1/CB2) present on the oocyte surface. This binding may activate the receptors, leading to the inhibition of adenylate cyclase, which, in turn, reduces ooplasm cAMP levels. Since high cAMP levels are critical to prevent premature meiotic resumption, its reduction caused by THC could result in the untimely, premature resumption of meiosis. This process increases the likelihood of chromosome misalignment and subsequent aneuploidy.

Implications for Fertility Counseling

These findings underscore the importance of increased awareness and caution among individuals with ovaries, especially those undergoing fertility treatments.

For patients undergoing IVF, exposure to THC could mean fewer euploid embryos available for transfer, which might prolong the time required to achieve a successful pregnancy. THC positivity was found to significantly decrease the odds of achieving a blastulation rate above 50% and a euploidy rate above 60%. Since embryo euploidy is strongly linked to successful implantation and healthy pregnancy, cannabis use may compromise reproductive outcomes by increasing the risk of IVF failure and miscarriage.

Fertility specialists are urged to routinely counsel patients on the potential risks of cannabis use. Experts advise patients attempting conception or undergoing IVF to avoid cannabis use, given that even occasional exposure may introduce THC into the follicular niche. Given the rising potency of cannabis products (some strains reach 30% THC), exposure to higher THC levels poses an increased risk of reproductive complications.

It is important to note that the study focused on oocytes collected during IVF, which may not perfectly reflect eggs maturing naturally, and it did not address the association of cannabis use with live birth outcomes. Further research is needed to determine how THC disrupts egg biology at the molecular level and to track pregnancy and live birth outcomes in larger studies. Ultimately, this research provides a strong basis for regulatory bodies, medical professional societies, and public health organizations to establish clear guidelines regarding cannabis consumption during fertility treatment.

Sources

9 September 2025. Nature Communications

• Cannabis impacts female fertility as evidenced by an in vitro investigation and a case-control study

9 September 2025. Science News

• Chemicals in marijuana may affect women’s fertility

9 September 2025. CNN

• Marijuana may cause chromosomal defects in human egg cells, study finds

9 September 2025. Technology Networks

• Cannabis Use Linked to Fertility Risks in Women

9 September 2025. Scimex

• Cannabis use may impact female fertility