Marrying a cousin or close relative raises the chance that both partners carry the same recessive gene, inherited from a shared ancestor. That shared genetic background is why children of consanguineous marriages have a higher chance of congenital anomalies, recessive genetic disorders, developmental delay, and recurrent miscarriage — and why the risk climbs the closer the blood relation is. This isn't about shaming a cultural practice; it's simple genetics, and it's manageable with the right counselling.
Why blood relation changes the genetic math
Every person carries some recessive genes without any effect on their own health, because a recessive condition only shows up when a child inherits two copies of the same faulty gene — one from each parent. Two unrelated people are unlikely to happen to carry the exact same rare recessive gene. Two people who share a recent common ancestor, however, are far more likely to have inherited the same gene from that shared ancestor, without either of them showing any sign of it. Marriage between relatives doesn't create new genetic risk — it raises the odds that a risk both partners were already silently carrying meets itself in their children.
What the risk actually looks like
- Closer relation, higher risk — the risk is highest for very close relations (such as first cousins) and lower as the blood relationship becomes more distant
- Congenital anomalies — structural differences present at birth occur somewhat more often in children of consanguineous marriages
- Recessive genetic disorders — conditions that need two copies of the same faulty gene to appear are the main driver of the added risk
- Developmental delay — some recessive conditions affect development, and the same shared-gene mechanism applies
- Recurrent miscarriage — certain genetic combinations are incompatible with a pregnancy continuing, which can show up as repeated pregnancy loss rather than a live-born condition
What you can actually do about it
- Premarital or preconception genetic counselling — a genetic counsellor can assess your specific family history and blood relation, not just apply a generic risk number
- Carrier screening — testing can identify whether you and your partner both carry the same recessive gene, which is far more informative than relying on family history alone
- IVF with PGT-A in selected couples — for couples identified as carrying a shared risk, IVF with preimplantation genetic testing can screen embryos before pregnancy begins, in cases where this is appropriate
- None of this requires giving up the marriage — it requires informed planning, ideally before conception rather than after a difficult pregnancy outcome
The point of raising this isn't to discourage a marriage that's already meaningful to a family — it's that informed couples can act on this risk before pregnancy, instead of discovering it afterward.
Frequently asked
Does marrying a cousin guarantee a child will have a genetic disorder?
No. It raises the probability compared to an unrelated couple, but it doesn't guarantee anything — most children of consanguineous marriages are born without any related condition. The point of counselling and screening is to understand and manage the added risk, not to predict a certain outcome.
Is the risk the same for all close relatives?
No — risk generally scales with how closely related the two people are. A more distant blood relation carries a smaller added risk than a very close one, which is why genetic counselling looks at the specific relationship rather than treating "related" as a single category.
We're already married — is it too late to do anything?
No. Genetic counselling and carrier screening are useful before any pregnancy, including a second or third one, not only before marriage. If you're planning a pregnancy, that's the right time to ask about it, regardless of how long you've been married.
What is PGT-A, and does every couple need it?
PGT-A is a genetic test performed on embryos created through IVF, used to check for certain chromosomal issues before an embryo is transferred. It isn't a routine requirement for every consanguineous couple — a genetic counsellor or fertility specialist can advise whether it's appropriate based on your specific carrier-screening results and family history.