Intra-family marriages and birth defects: Are genetic risks being overlooked?

Intra-family or consanguineous marriages remain a common practice across regions, cutting across rural and urban settings as well as educated communities. While often viewed as culturally familiar and socially convenient, expert warns that such unions may carry a higher risk of congenital anomalies in babies due to shared genetic factors.

Genetic risks and rising incidence of anomalies

According to Dr. Nirmala Chandrashekar, consultant- Obstetrics & Gynaecology at Fortis Hospital (Bengaluru) intra-family or consanguineous marriages continue to be practiced across many parts of India including urban communities and even among educated families. Despite better awareness, many families still choose such marriages because they feel it is convenient, familiar and safe.

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"Scientifically, the concern arises from shared genes. Close relatives often carry similar genetic material. Every person carries some recessive or “silent” faulty genes that do not cause illness unless both partners carry the same one. When two related people marry, the chance that they both have the same recessive gene is higher. If both pass this gene to the baby, it can lead to birth defects or congenital anomalies," said Dr Chandrashekar.

A major study by the National Institutes of Health (NIH) has shown that the risk of congenital anomalies increases from around 0.7% in non-related marriages to up to 3.8% in consanguineous marriages. Also, consanguinity can reduce genetic diversity, increasing the expression of harmful genes and lowering immunity, which may raise vulnerability to infectious diseases and multifactorial conditions like heart disease and diabetes.

Dr Chandrashekar further said that there are also different degrees of consanguinity. First-degree relationships like brother–sister are legally prohibited. Second-degree relationships, such as first cousins and third-degree relationships, like children of maternal uncles or aunts are still seen in some communities. As the biological relationship becomes closer, the chances of genetic disorders, developmental delays, metabolic diseases and physical anomalies in babies increase, she added.

Biologically, this happens because close relatives share a larger portion of DNA, which raises the likelihood that both partners carry the same harmful recessive gene, she said, adding that when a baby receives two copies of this gene, the condition becomes active and can lead to congenital or inherited disorders. In unrelated marriages, this overlap of faulty genes is much less likely.

Emotional and social impact on families

When a child is born with congenital anomalies, the emotional impact on parents can be significant. Families may experience shock, guilt, fear, and uncertainty about the child’s future. Many worry about long-term care, financial strain, social stigma, and whether their child will live an independent life. These psychological challenges often add to the medical difficulties the baby may face.

To reduce risks, families can consider pre-marital or pre-pregnancy genetic counselling, carrier testing for couples who are related and regular prenatal screening to detect anomalies early. Creating awareness and encouraging open conversations about genetic risks can help families make informed decisions that protect the health and future of their children, Dr Chandrashekar added.