M5-Lecture2 Flashcards
ART
Replacement level fertility is the totalfertilityrate—the average number of children born per woman—at which a population exactly replaces itself from one generation to the next, without migration.
the inability of a sexually active, non-contracepting couple to achieve pregnancy in one year
Infertility
any form of reduced fertility with prolonged time of non-conception
Subfertility
medical procedures primarily used to address infertility
ART
Around 80% of pregnancies occur within the first 6 months of regular unprotected intercourse, and if conception takes longer than this, it may indicate subfertility.
True
Only half of the pregnancies are planned?
True
1 in 6 Canadian couples experience infertility:
True
Causes of Subfertility/Infertility- Female
Problems producing eggs:
- ovulation disorders
- reduced ovarian reserve
- irregular or no menstrual cycle
Tubal factor infertility:
- Egg and/or sperm can’t travel
Implantation failure:
See it if necessary
Low sperm quality or quantity: 40%
- Varicocele: enlargement of scrotal veins (common)
Poor sperm transport: 10%, 20%
- Vas deferens blockage
- Slow sperm
- Semen hyper-viscosity
Ageing
Lifestyle
Physio-pathology, environmental
Hormones, obesity, Being underweight, other chronic illnesses
STIs
Drugs, Advanced maternal AND paternal age
Truth: Sperm quality decreases with age.
ART types:
Ovulation induction (fertility drugs)
Intrauterine insemination (IUI)
In vitro fertilization (IVF)
Intra-cytoplasmic sperm injection (ICSI)
Third-party assisted ART
Egg/sperm freezing and storage
IUI
In male and female infertility
Sperm directly placed in uterus (for low sperm count, anti-sperm antibodies)
No medication required
Before and after ovulation
IVF
Egg and sperm fertilized outside uterus
See more if needed
Steps:
- Hormone treatment induce ovulation
- Eggs obtained from ovaries
- mixed with sperm outside uterus
- Fertilized egg placed in an incubator for 48 hours (embryo develops)
- Fresh ones Implanted in uterus.
ICSI
Used in conjunction with IVF
due to unsuccessful IVF, low sperm, poor sperm, vasectomy, anti-sperm antibodies
Steps:
- Ovaries stimulated, eggs retrieved.
- Sperm collected and assessed for quality
- Cumulus cells removed from egg (to assess egg maturity). Need to be genetically mature.
- Single sperm injected into mature egg.
- Egg placed in an incubator, allow fertilization and embryo growth.
other technologies:
Three parent babies
mtDNA screening + IVF
Spermbots
Egg by mt transfer
3-parent IVF is a technique that allows women with mitochondrial diseases to have healthy children by transferring their nuclear DNA into a donor egg with healthy mitochondria, which is then fertilized with the father’s sperm. This results in a child with genetic material from three sources: the mother’s nuclear DNA, the father’s nuclear DNA, and the donor’s mitochondrial DNA.
mtDNA Screening + IVF
high levels of mtDNA in embryo are associated with implantation failure
Screen blastocysts for mtDNA levels select and implant only those blastocysts with appropriate mtDNA levels
Could increase IVF efficiency and success rates
Steps:
1. Hormones injected to stimulate egg production
2. Eggs are collected from ovary
3. Eggs and sperm combined - fertilization
4. Five-day embryos used
5. Chromosomal screening or testing levels of mtDNA, before implantation
Egg ‘Rejuvenation’
Rationale: mt in some eggs (esp in women >35) contribute to poor embryo viability
Harvest younger (presumably healthier) mt from egg precursor cells
Augment ‘old’ eggs by injecting ‘younger’ mt from precursor into the eggs to replace ‘ageing’ mt
Hope is to improve embryo quality and viability
Experimental – not in clinical practice
Steps:
1. Egg precursor cells taken from biopsy ovary
2. Precursor cells cultured and frozen
3. Mt from precursor cells injected with into IVF egg.
especially in women over 35 years.
Spermbots
Rationale: motorized apparatus to assist with sperm delivery and fertilization
Metal-coated polymer microhelices
For male infertility – but no clinical application yet
Bionic suits for sperm. help with sperm motion
Steps: capture, transport, release
See diagram
Female Reproductive Tract Fluid
Oviduct and uterine fluids play a crucial role in embryo development by supplying nutrients, including amino acids like BCAAs (leucine, isoleucine, and valine). A low-protein diet in mice reduces BCAAs in both uterine fluid and plasma during blastocyst formation, impacting metabolic signaling and growth through the mTOR pathway.
Oviductal Fluid
As early embryos travel through the oviduct, they undergo extensive DNA methylation reprogramming, which can be influenced by factors in the oviductal environment. Bovine embryos cultured with oviductal fluid exhibit changes in DNA methylation and mRNA expression of key developmental genes in blastocysts, suggesting long-term effects on embryo development.
see diagram
Other Fluids & Pregnancy Rates in ART
Intercourse during an IVF cycle may improve pregnancy rates by enhancing embryo development and implantation, with exposure to semen around embryo transfer increasing the proportion of viable embryos. Seminal plasma, previously seen as a nutrient source for sperm, is rich in hormones (like E2, PGs, and testosterone), signaling molecules (such as TGF-β), and cytokines, and TGF-β concentrations in seminal plasma are among the highest found in biological fluids.
Reproductive Tract Microbiomes
The composition of the seminal bacterial community is linked to semen health and male fertility. Distinct microbial communities are present along the female reproductive tract, with certain taxa associated with reproductive tract diseases and influencing rates of implantation, pregnancy, and live births.
Increased time to achieve pregnancy alone is associated with an increase in abruption, preeclampsia, C-section, and placenta previa
Or maternal factors, like obesity:
Evidence is mixed, but getting clearer
Beyond pregnancy outcomes, ART may be associated with increased risk for poor health outcomes in offspring
The artificial environment is very different from the natural one
Fresh vs. Frozen Embryo Transfer
No differences in pregnancy and live birth rates
Single blastocyst transfer differences:
fresh transfer was also associated with increased rates of preterm birth.
While frozenL high weight at birth
Impact of Culture Media
It’s sort of stressful in that dish!
Differences or fluctuations in:
Nutrients/energy sources
Hormones
Antibiotics
Ions
Other ingredients?
Oxygen
pH
Temperature
Light exposure
Contained
Handling
Medium overlay
Time
Different culture media can explain differences in pregnancy rates and birthweights
Difference in birthweights in babies cultured (as embryos) in two common culture media.
Birthweight difference was 200g
This is a similar difference in birthweight seen between non-smoking women and women who smoke during pregnancy!!!
A study comparing two commonly used culture media in ART protocols found that the media alone could explain differences in pregnancy rates and birth weights, with a 200-gram difference in birth weight between the two groups. This significant change in birth weight, similar to the effects seen between smokers and non-smokers, highlights the critical role of culture media during early embryo development.
see diagram
A follow-up RCT comparing two common ART culture media (G5 and HTF) with over 400 babies found that G5 media led to more viable embryos for transfer, higher implantation rates, and better clinical pregnancy outcomes. However, babies cultured in G5 had lower birth weights (158 grams on average) and a higher rate of premature singletons, highlighting the importance of the culture environment on both short-term health outcomes and the need for transparency in the composition of culture media used in ART.
A study investigating the long-term cardiovascular outcomes of embryo culture and transfer in mice found that embryos created through ovarian hyperstimulation (common in ART) exhibited lasting effects on postnatal physiology. Mice from the culture and transfer group developed hypertension in adulthood, highlighting how ART procedures can influence long-term health outcomes.
Follow-up of 8-18 year old IVF & control children born to sub-fertile parents:
Blood pressure and fasting glucose levels differ between IVF and control children
Differences were not due to current risk factors, early life factors, parental characteristics or cause of parental subfertility.
General vascular dysfunction in otherwise healthy children conceived by ART
A follow-up study of children born via IVF and spontaneous conception from sub-fertile parents found differences in blood pressure and fasting glucose levels, suggesting long-term effects of the ART procedure itself, rather than parental factors or infertility. The study used sophisticated statistical modeling to control for potential confounders and concluded that the observed physiological differences were linked specifically to the ART process.
Mouse embryo culture and embryo transfer is associated with hypertension in adulthood
Cross-sectional study of 14-year old children born after ICSI or spontaneous conception (SC)
↓ awakening cortisol levels in pubertal ICSI females (but not males) vs. SC
Could ART conception (re)program HPA development or function
A cross-sectional study of 14-year-old children born through ICSI or spontaneous conception found that pubertal females conceived via ICSI had lower awakening cortisol levels compared to their spontaneously conceived counterparts, suggesting alterations in HPA axis function. These findings, the first to report such changes in teenagers born after ART, could not be explained by maternal, birth, or child characteristics, pointing to the conception environment as a potential programming stimulus for HPA function.
Diet, microbes & sperm!
High fat diet is associated with altered seminal plasma microbiome
What do these microbes do?
Intrauterine environment
Metabolites and nutrition
Recent studies, including the one you just saw, suggest that paternal diet can significantly impact the microbiome within seminal plasma, with low-protein and high-fat diets causing notable alterations. While the exact functional significance of the seminal plasma microbiome is still unclear, it is believed that it may influence male reproductive health and the early uterine environment by affecting metabolite profiles, which could, in turn, impact ART success and long-term health outcomes. Understanding these complex factors is crucial for creating a healthy microenvironment for artificial conception.
High fat diet reduced lifespan in ART-conceived mice
The data presented suggests that the periconception environment, including ART exposure, can indeed program offspring in ways that may affect their lifelong health risks. A study in mice found that while natural and IVF-conceived offspring had similar lifespans when fed a normal diet, IVF offspring showed reduced survival when both groups were challenged with a high-fat diet, highlighting the importance of multiple environmental “hits” in disease development.
Are there consequences for the individual born to older fathers?
. As many parents are increasing in age we’re now starting to ask are there consequences for the individual born to an older parent and even more so asking are there consequences for the individual born to an older father
Risk of infertility also
A large study using data from over 40 million live births in the US between 2007 and 2016 examined the impact of paternal age on perinatal outcomes. The study found that older fathers (over 45, and especially over 55) were associated with worse outcomes, including shorter gestational age, higher risk of preterm birth, low birth weight, and lower Apgar scores, even after adjusting for confounding factors such as maternal age, race, and smoking status.
See diagram
The study also found that advanced paternal age was linked to an increased risk of gestational diabetes in mothers, further highlighting the potential impact of paternal age on both maternal and offspring health outcomes.
Greater odds of pregnancy complicated by gestational diabetes with older paternal age (↑28% if father >45 years of age).
See diagrma
As men age, the high number of germ cell divisions can lead to epigenetic changes in spermatocytes, including disruptions in histone methylation, which may affect embryonic and placental development. Paternal imprinting can influence fetal growth and maternal pregnancy outcomes, potentially contributing to adverse health effects.
The mechanisms underlying adverse pregnancy and offspring outcomes related to advanced paternal age likely involve both genetic and epigenetic factors. The high number of germ cell divisions in aging fathers increases the risk of genetic abnormalities, including autism, psychiatric conditions, and perinatal morbidity. Epigenetic changes, such as disruptions in histone methylation in spermatocytes, may affect embryo and placental development, while paternal imprinting could influence fetal growth, pregnancy health, and overall pregnancy outcomes.
A meta-analysis of a Swedish birth cohort of over 1 million people found that the risk of autism increased with paternal age. Offspring of men aged 50 and older were 2.2 times more likely to have autism compared to those of fathers aged 29 or younger, even after controlling for maternal age and other autism risk factors. Additionally, in families with discordant siblings, the affected sibling tended to have an older father, even after adjusting for maternal age and parity.
A large meta-analysis using Swedish cohort data, including nearly 900 autism cases from 600 families, found that the risk of autism increased with paternal age. Offspring of fathers aged 50 or older were over two times more likely to develop autism compared to those of fathers aged 29 or younger, even after controlling for maternal age and other autism risk factors. Additionally, in families with discordant siblings (one affected by autism and the other not), the affected sibling had an older father, suggesting that paternal age plays a role in autism risk.
Schizophrenia risk increased in offspring of older fathers ≥30 yrs vs reference paternal age 25-29 yrs
A large meta-analysis of 12 studies found that the risk of schizophrenia in offspring increases with paternal age. Specifically, children of fathers aged 30 or older had a 1.7 times higher relative risk of developing schizophrenia compared to those with fathers aged 25-29. Interestingly, the study also observed a U-shaped curve, where both very young and older paternal age were associated with an increased risk of schizophrenia, particularly in male offspring. The population attributable risk was calculated at 10% for fathers aged 30 and older, and 5% for fathers under 25 years of age.
The increased risk of psychiatric disorders like autism and schizophrenia associated with paternal age is likely due to epigenetic changes rather than the inheritance of mutated DNA. Studies suggest that these disorders are influenced by both genetic and environmental factors, and persistent changes in gene expression observed in affected individuals point to epigenetic modifications as the key mechanism. These changes may affect gene regulation without altering the DNA sequence itself, potentially impacting offspring and even subsequent generations.
The mechanisms linking advanced paternal age to conditions like autism and schizophrenia remain largely unclear, but epigenetic changes are a promising area of study. Since these psychiatric disorders are influenced by both genetic and environmental factors, it’s thought that persistent alterations in gene expression—rather than the inheritance of mutated DNA—could play a role in these outcomes. However, much of the underlying biology is still not fully understood, and there’s a lot more research to be done to unravel the details.
