Declining Twinning Rates in India by 2100: Public Health Challenges and the Need for a National Twin Registry

Why in News

A recent modelling study published in the journal Human Reproduction predicts a 10.5% decline in India's twinning rate by 2100 due to falling fertility rates, yet the country will still account for the world's largest share of twin births (23.4%) owing to its massive population size. This has significant public health and demographic implications, as twins face higher mortality risks, and experts are calling for a national twin registry to study environmental factors like pollution alongside genetics, drawing parallels from China's approach to twin research.

Key Points

1. The twinning rate in India, currently at 1.06% (number of twin births per 1,000 deliveries), is projected to fall to 0.92% by 2100, a decline of 10.5%, primarily due to overall fertility dropping below replacement levels and fewer women giving birth.
2. Despite the rate decline, India will maintain the largest global share of twin births at 23.4% among low- and middle-income countries by 2100, driven by its population growth, while Bangladesh is expected to see a steeper 20.2% drop.
3. The study, based on data from over three million births in 39 low-income countries (1980-2020) from Demographic and Health Surveys (DHS) and World Fertility Surveys (WFS), may underestimate future rates as it excludes the rising use of medically assisted reproduction (MAR), including IVF, which can boost twinning by 40-50%.
4. In high-income countries, MAR has been a key driver of rising twinning rates, but in low-income settings like India, natural factors such as older maternal age (increasing dizygotic twins) play a larger role, though MAR adoption is growing.
5. A separate Harvard-led study using National Family Health Survey (NFHS) data (1993-2021) shows India's twinning rate rose from 0.9% to 1.5%, with twins accounting for 7.7% of under-five deaths despite being a small birth proportion, and mortality at 179.8 per 1,000 live births in 2021.
6. Twins in India face 7.5 times higher early neonatal mortality and 10 times higher late neonatal mortality than singletons, with risks varying by household wealth, birth order (higher for first/second pregnancies), and emphasizing the need for targeted health interventions.
7. Public health implications include higher risks in twin pregnancies for mothers and babies, necessitating better preparation; experts highlight twins as a vulnerable group contributing disproportionately to child mortality.
8. A 2022 paper by AIIMS, ICMR, and Mayo Clinic researchers calls for a national twin registry in India to track health, development, and environmental impacts, similar to registries in Sweden (30 ongoing projects on cancer, dementia) and Denmark.
9. Drawing from China's National Twin Registry, which studies pollution's role in diseases like asthma and COPD, Indian experts suggest twin studies could reveal how urbanization and air pollution interact with genetics in airborne inflammatory conditions.
10. Globally, twinning rates provide insights into fertility patterns, maternal age changes, and treatments; low-income countries show higher natural dizygotic twinning due to nutrition and genetics, while monozygotic twins remain constant at 0.4%.

Explained

What is the Twinning Rate and Why is it Important for Public Health and Demography?

Definition of Twinning Rate: The twinning rate refers to the number of twin births per 1,000 deliveries, indicating how common twin pregnancies are in a population; it includes both monozygotic (identical twins from one egg) and dizygotic (fraternal twins from two eggs) types, with dizygotic being more variable due to environmental and genetic factors.

Public Health Significance: Twin pregnancies are riskier, with higher chances of preterm birth, low birth weight, and complications for mothers (e.g., preeclampsia) and babies (e.g., respiratory distress); in India, twins face 7.5-10 times higher neonatal mortality, contributing 7.7% to under-five deaths despite low birth rates.

Demographic Insights: Twinning rates reflect fertility trends, maternal age (older mothers have more dizygotic twins), nutrition, and use of fertility treatments; monitoring helps predict population growth and resource needs, especially in low-income settings where data is scarce.

Global Context: High-income countries have seen rises due to MAR, while low-middle-income countries (LMICs) like India show natural variations; globally, twinning affects 1-2% of births, but risks make it a key indicator for child survival goals like SDG 3.2.

What Does the Recent Study Predict About Twinning Rates in India and LMICs?

Study Methodology: Researchers from Max Planck Institute and Swedish Collegium analyzed 3 million+ births from 39 LMICs (1980-2020) using DHS and WFS data, modeling future rates based on maternal age patterns and UN population projections up to 2100.

Projections for India: Twinning rate to decline from 1.06% to 0.92% by 2100 (10.5% drop) due to fertility below replacement (fewer births overall), but India will have 23.4% of global twin births in LMICs owing to population size; underestimation possible as MAR growth (e.g., IVF clinics rising from 500 in 2010 to 2,500+ in 2025) not factored.

Trends in Other LMICs: Absolute twin births will rise in many due to population growth, but rates may stabilize or fall in South Asia (e.g., 20.2% decline in Bangladesh); older maternal age partially offsets declines, as women over 30 have higher dizygotic twinning odds.

Comparison with High-Income Countries: There, rates peaked at 1.5-2% due to MAR but fell post-2000s with single-embryo transfers; LMICs have lower baseline (0.8-1.2%) but rising potential from delayed childbearing and urbanization.

What Are the Public Health Challenges Associated with Twin Births in India?

Rising Trends from NFHS Data: Harvard study (1993-2021) shows twinning rose from 0.9% to 1.5%, aligning with global increases; twins' under-five mortality dropped but remains high at 179.8/1,000 vs. singletons, with 7.7% of deaths from twins.

Higher Risks and Vulnerabilities: Early neonatal death 7.5x higher, late neonatal 10x; risks vary by wealth (poorer households worse), birth order (first/second pregnancies riskier for twins), and access to care; preterm births (60% in twins vs. 10% singletons) drive this.

Resource Implications: Twins strain health systems with needs for NICUs, monitoring; in India, with 27 million annual births, even 1.5% twinning means 400,000+ twins yearly, amplifying child mortality (IMR at 28/1,000 in 2023).

Policy Recommendations: Train ASHA workers for twin care, treat twins as vulnerable group; integrate into programs like RCH for better outcomes, addressing SDG gaps.

What is the Role of Environmental Factors Like Pollution in Twin Studies?

Chinese National Twin Registry: Established to study environmental exposures; twins respond differently to pollution based on location, revealing gene-environment interactions in diseases like asthma, COPD, and inflammatory conditions.

Relevance to India: With urbanization (35% urban in 2025, projected 50% by 2050) and high pollution (AQI often 200+ in cities), twin studies could assess how air pollution (PM2.5, NO2) influences immune systems, diet, and gut microbiome; e.g., Delhi's pollution linked to 30% rise in respiratory cases.

Broader Theory: Twins (especially monozygotic) control for genetics, isolating environmental effects; dizygotic twins show heritability; this "nature vs. nurture" approach aids precision medicine, as seen in Swedish/Danish registries studying cancer and allergies.

Indian Context: Pollution causes 1.7 million deaths yearly (Lancet 2020); twins could map urban-rural differences, supporting policies like NCAP (National Clean Air Programme).

Why is a National Twin Registry Needed in India?

Proposal from 2022 Paper: AIIMS-ICMR-Mayo Clinic researchers advocate a registry to track twins' health, development, and economics; highlights experiences from Sweden (30 projects on dementia, CVD) and Denmark (cancer, cognitive studies).

Benefits for Research: Enables longitudinal studies on genetics vs. environment; e.g., pollution's role in twins could inform public health; registries provide data for policymaking, improving survival (twin IMR 5x higher globally).

Global Models: Sweden's registry (85,000 pairs) explores gene-environment in Parkinson's; Denmark's (140,000 pairs) studies hormones and memory; India's large twin population (projected millions by 2100) makes it ideal for diverse data.

Implementation Challenges: Privacy, funding (est. Rs 100 crore initial), integration with NFHS; could start pilot in high-twinning states like Uttar Pradesh, leveraging Aadhaar for tracking.

What Are the Types of Twins and Their Underlying Biology?

Monozygotic (Identical) Twins: From one fertilized egg splitting; genetically identical, constant rate (0.4% globally); used to study environment's role as differences arise from epigenetics/lifestyle.

Dizygotic (Fraternal) Twins: From two eggs fertilized separately; genetically like siblings (50% shared DNA), influenced by maternal age, nutrition, height, BMI; higher in Africa (1.6%), lower in Asia (0.8%).

Factors Influencing Twinning: Older age (30+) raises FSH hormone, increasing multiple ovulations; MAR boosts dizygotic; genetics (e.g., African descent higher); nutrition (yams in Nigeria linked to higher rates via phytoestrogens).

Risks and Theory: Twins share placenta/uterus, leading to competition; "vanishing twin syndrome" (one absorbs other); evolutionary theory sees dizygotic as adaptation for high-fertility environments.

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