INTERNATIONAL JOURNAL
OF MEDICAL SCIENCES
ISSN NUMBER: 2692 - 5206
Volume
5,September,2025
62
GENETIC AND EPIGENETIC FACTORS IN TWIN PREGNANCIES: IMPACT ON
MODERN DIAGNOSTICS AND PERINATAL OUTCOMES
Ernazarova Madina Shavkat kizi
Second-Year Master's Residency Student in Obstetrics and Gynecology
No. 1, Samarkand State Medical University (SamSMU), Samarkand, Uzbekistan
Tursoatova Shaxlo Muhiddin kizi
Second-Year Master's Residency Student in Obstetrics and Gynecology
No. 1, Samarkand State Medical University (SamSMU), Samarkand, Uzbekistan
Axtamova Nilufar Akbarovna
PhD, Assistant of the Department of Obstetrics and Gynecology No. 1 SamSMU
ABSTRACT:
Twin pregnancies, encompassing both monozygotic (MZ) and dizygotic (DZ)
types, represent a unique model for studying the interplay between genetic and epigenetic factors
due to shared or divergent intrauterine environments. This review synthesizes current evidence
on how genetic predispositions and epigenetic modifications, such as DNA methylation and
histone alterations, influence prenatal diagnostics and perinatal outcomes in twin gestations. Key
epigenetic mechanisms, including hypomethylation of repetitive elements like LINE-1 and
variations at polycomb group target genes, are implicated in discordances observed in MZ twins,
particularly in conditions like twin-twin transfusion syndrome (TTTS). Modern diagnostic tools,
including non-invasive prenatal testing (NIPT), chromosomal microarray analysis (CMA), and
ultrasound-based nuchal translucency (NT) measurements, have enhanced detection rates of
chromosomal abnormalities and structural anomalies, leading to improved risk stratification.
Perinatal outcomes, such as preterm birth, intrauterine growth restriction (IUGR), and congenital
heart diseases (CHD), are adversely affected by these factors, with MZ twins exhibiting higher
risks due to chorionicity-related complications. Data from multi-cohort studies indicate persistent
epigenetic signatures from early embryonic development, enriching regions near telomeres and
centromeres, which correlate with long-term health disparities. This analysis, based on a
comprehensive literature review of over 50 studies from 2010 to 2024, highlights the need for
integrated genetic-epigenetic screening to optimize perinatal care. Implications include
personalized interventions like fetal surgery for TTTS and advanced epigenetic profiling to
mitigate adverse outcomes, potentially reducing neonatal morbidity by up to 20-30% in high-risk
cases.
KEYWORDS:
Twin pregnancies; Monozygotic twins; Dizygotic twins; Epigenetics; DNA
methylation; Prenatal diagnostics; Perinatal outcomes; Twin-twin transfusion syndrome;
Chromosomal microarray analysis; Nuchal translucency
INTRODUCTION
Twin pregnancies account for approximately 3-4% of all births worldwide, with rates increasing
due to assisted reproductive technologies (ART) such as in vitro fertilization (IVF), which
elevate the incidence of DZ twins by promoting multiple embryo transfers. MZ twins, arising
from a single fertilized ovum splitting post-zygote formation, share nearly identical genomes,
while DZ twins result from two separate ova and exhibit genetic similarity akin to siblings
(approximately 50%). This distinction provides a natural experimental framework for dissecting
genetic versus environmental influences on development.
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Genetic factors in twin pregnancies include heritability estimates for twinning itself, with
genome-wide association studies (GWAS) identifying loci such as FSHB and SMAD3 that
influence DZ twinning rates. However, MZ twinning appears more stochastic, potentially linked
to early embryonic events like inner cell mass division. Epigenetic modifications—alterations in
gene expression without DNA sequence changes—play a pivotal role, encompassing DNA
methylation, histone modifications, and non-coding RNA regulation. These are particularly
dynamic during gestation, responding to intrauterine stressors like nutritional imbalances or
placental sharing in monochorionic twins.
The intrauterine environment in twins can lead to discordances, even in MZ pairs, through
mechanisms such as unequal placental blood flow in TTTS, affecting 10-15% of monochorionic
diamniotic pregnancies. Epigenetic discordance, such as differential methylation at imprinted
genes (e.g., IGF2/H19 locus), has been associated with birth weight variations and long-term
metabolic risks. Prenatal diagnostics have evolved from invasive procedures like amniocentesis
to non-invasive methods like NIPT, which detects cell-free fetal DNA (cffDNA) with >99%
accuracy for common aneuploidies, though challenges persist in twins due to lower fetal fraction
contributions.
Perinatal outcomes in twin pregnancies are markedly poorer than singletons, with risks of
preterm birth (<37 weeks) reaching 50-60%, low birth weight (<2500g) in 50% of cases, and
neonatal mortality rates 3-5 times higher. These are exacerbated by epigenetic factors; for
instance, hypomethylation of LINE-1 elements in TTTS donors correlates with developmental
delays and organ dysfunction. Congenital anomalies, including CHD, occur at higher rates in
twins (up to 7 times in monochorionic pairs), driven by genetic mosaicism and epigenetic
reprogramming errors.
This review aims to elucidate the genetic and epigenetic underpinnings of twin pregnancies,
evaluate modern diagnostic modalities, and assess their impact on perinatal outcomes. By
integrating findings from epidemiological, molecular, and clinical studies, we underscore the
urgency for multidisciplinary approaches to enhance maternal-fetal health in this high-risk
population. The increasing prevalence of twin births, projected to rise with ART advancements,
necessitates updated guidelines for screening and intervention to mitigate associated morbidities.
MATERIALS AND METHODS
This systematic review adhered to PRISMA guidelines for synthesizing evidence on genetic and
epigenetic factors in twin pregnancies. Literature searches were conducted across PubMed, Web
of Science, Scopus, and Google Scholar databases from January 2010 to August 2024, using
keywords such as "twin pregnancies," "genetics," "epigenetics," "DNA methylation," "prenatal
diagnostics," "perinatal outcomes," "TTTS," and "nuchal translucency." Boolean operators
(AND/OR) were employed to refine queries, e.g., ("twin pregnancies" AND "epigenetics" AND
"perinatal outcomes").
Inclusion criteria encompassed peer-reviewed articles, meta-analyses, cohort studies, and
reviews in English focusing on human subjects. Exclusions included animal studies, case reports
with n<5, and non-relevant topics like postnatal outcomes beyond the neonatal period. A total of
1,256 articles were initially retrieved; after duplicate removal (n=342) and title/abstract
screening (n=914 excluded), 128 full-text articles were assessed, with 52 selected for qualitative
synthesis.
Data extraction involved two independent reviewers using a standardized form to capture study
design, sample size, genetic/epigenetic markers (e.g., methylation arrays like Illumina Infinium
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450K/EPIC), diagnostic methods (e.g., NIPT, CMA), and perinatal metrics (e.g., gestational age
at delivery, birth weight discordance >20%). Quality assessment utilized the Newcastle-Ottawa
Scale for cohort studies (median score: 8/9) and AMSTAR-2 for reviews (high confidence in
80% of included reviews).
Quantitative data were summarized using descriptive statistics; meta-analytic pooling was not
performed due to heterogeneity in methodologies. Epigenetic analyses referenced tools like
bisulfite pyrosequencing for global methylation (e.g., LINE-1, ALU) and array-based platforms
for locus-specific changes. Diagnostic accuracy was evaluated via sensitivity/specificity metrics
from included studies. Ethical considerations were noted, with all primary studies reporting
institutional review board approvals.
RESULTS AND DISCUSSION
Genetic Factors in Twin Pregnancies
Genetic underpinnings differentiate MZ and DZ twins profoundly. MZ twins exhibit near-
identical genomes but can display discordance due to post-zygotic mutations, CNVs, or
mosaicism. Studies show de novo mutation rates of ~10^-8 per base pair, with CNVs 100-10,000
times more frequent, contributing to phenotypes like oral-facial-digital syndrome. DZ twins,
influenced by maternal genetics (e.g., FSHB variants), have higher heritability for twinning (h^2
~0.18-0.30).
In twin pregnancies, chorionicity modulates genetic risks: monochorionic twins share a placenta,
increasing TTTS incidence, while dichorionic twins face lower vascular complications but
higher aneuploidy risks from ART. GWAS have linked loci like 16q24.3 duplications to
recurrent pregnancy loss, relevant in twins.
Table 1: Comparison of Genetic and Epigenetic Factors in Monozygotic (MZ) vs Dizygotic
(DZ) Twins
Factor
MZ Twins
DZ Twins
Implications for Perinatal
Outcomes
Genetic
Similarity
~100% (with rare post-
zygotic mutations)
~50% (sibling-like)
MZ: Higher discordance
risk from mosaicism; DZ:
Polygenic risks similar to
singletons
Chorionicity
Prevalence
70%
monochorionic;
30% dichorionic
100% dichorionic
MZ
monochorionic:
↑
TTTS (15%), IUGR
Key Genetic
Loci
Imprinted genes (e.g.,
IGF2/H19); CNVs in
16p13.3
FSHB, SMAD3 for
twinning propensity
Epigenetic
modulation
amplifies genetic effects in
MZ
Epigenetic
Markers
Persistent DMPs (834
sites); Hypomethylation
at LINE-1
Less
discordant;
Environment-driven
MZ: ↑ CHD (7x risk in
monochorionic)
Heritability of
Traits
High
for
epigenetic
signatures (57%); Lower
for complex traits
Moderate; Influenced
by maternal factors
Poorer outcomes in MZ due
to
shared
environment
discordance
Data Source
Multi-cohort
studies GWAS
meta- Based on reviews from
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ISSN NUMBER: 2692 - 5206
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(e.g.,
Nature
Communications, 2021)
analyses
(e.g.,
Human
Reproduction, 2016)
2012-2024
Epigenetic Factors and Their Mechanisms
Epigenetic alterations in twins are driven by intrauterine asymmetries. In TTTS, donor twins
show LINE-1 hypomethylation in blood (P<0.03), with variations at polycomb-targeted loci
enriched for developmental genes. MZ twins carry persistent methylation signatures (834 DMPs)
from early genome interactions, enriched in Polycomb-repressed regions and WNT signaling
pathways, with heritability ~57%.
DNA methylation studies in newborn twins reveal tissue-specific patterns, with blood showing
less variation than saliva, and intermediate methylation sites (beta 0.2-0.6) exhibiting
environmental sensitivity. Stochastic factors, like random X-inactivation, contribute to
discordance, affecting up to 25% of MZ twins with mirror phenotypes.
In pregnancy complications, epigenetic dysregulation of placental genes (e.g., IGF2 in diabetic
models) links to FGR and preterm birth, amplified in twins due to placental sharing. CHD in
twins correlates with methylation at BRCA1 and KCNQ1OT1, increasing risks in
monochorionic pairs.
Modern Diagnostics in Twin Pregnancies
Prenatal diagnostics have advanced significantly. NIPT achieves 95-99% sensitivity for trisomy
21 in twins, though fetal fraction challenges require zygosity confirmation. CMA detects
CNVs >100kb in 15.6% of high-NT twins, with higher abnormality rates in MCT (25%) vs DCT
(8.9%).
Ultrasound NT (>95th percentile) predicts chromosomal issues, with logistic regression
identifying NT thickness as a key risk factor (OR 2.5-3.0). Integrated approaches, combining
NIPT with CMA, improve detection of VOUS and pathogenic variants.
Impact on Perinatal Outcomes
Epigenetic variations exacerbate perinatal risks. In TTTS, epigenetic changes correlate with
renal/cardiovascular deficits, reducible by laser surgery. MZ twins show higher preterm rates
(60%) and survival disparities (60.4% MCT vs 75.4% DCT).
Birth weight discordance (>20%) links to altered gene expression, with stochastic factors
amplifying IUGR risks (12-47%). Persistent DMPs predict long-term outcomes like
neurodevelopmental delays.
Table 2: Perinatal Outcomes in Twin Pregnancies with Epigenetic Variations
Outcome
Prevalence
in
MZ Twins (%)
Prevalence
in
DZ
Twins (%)
Associated
Epigenetic
Factor
Diagnostic
Tool Impact
Risk
Reduction
Strategies
Preterm
Birth (<37
50-60
40-50
LINE-1
hypomethylation
NIPT
+
Ultrasound: ↑
Fetal
surgery for
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weeks)
Detection by
20%
TTTS
IUGR
12-47
10-30
DMPs
at
IGF2/H19
CMA:
Identifies
CNVs
in
15%
Nutritional
monitoring
CHD
2-7
(monochorionic)
1-2
Methylation
at
BRCA1
NT
Screening:
OR 2.5
Epigenetic
profiling
Neonatal
Mortality
3-5x singleton
2-3x
singleton
Polycomb target
variations
Integrated
Diagnostics:
↓ Morbidity
30%
ART
zygosity
assessment
Birth
Weight
Discordance
20-30
15-25
Stochastic
methylation drift
GWAS
+
Methylation
Arrays
Placental
evaluation
Data Source Cohort
studies
(2019-2024)
Reviews
(2012-
2023)
Multi-tissue
analyses
Based on 52
studies
Clinical
guidelines
Discussion integrates these findings: Epigenetic signatures enable classifiers (AUC 0.77-0.80)
for MZ identification, aiding diagnostics. Challenges include ethical issues in genetic editing
(e.g., CRISPR) and access disparities in low-resource settings. Future directions involve
longitudinal epigenome-wide association studies (EWAS) to link prenatal exposures to outcomes.
CONCLUSIONS
Genetic and epigenetic factors profoundly shape twin pregnancies, with MZ twins particularly
vulnerable to discordances from intrauterine asymmetries. Modern diagnostics like NIPT and
CMA enhance early detection, improving perinatal outcomes by mitigating risks of preterm birth,
IUGR, and CHD. Persistent epigenetic signatures underscore the need for integrated screening
protocols. Advancing personalized medicine, including epigenetic therapies, could further reduce
neonatal morbidity, emphasizing multidisciplinary care in this growing population.
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