LONDON — British couples can create babies through in vitro fertilization to help cure sick siblings, Britain's highest appeal court ruled yesterday, rejecting a challenge from an anti-abortion group.

The Law Lords backed a 2003 Court of Appeal ruling that some couples undergoing the fertility treatment could have their embryos screened to find tissue matches for seriously ill children.

Advocates say the procedure will help save desperately ill children. Opponents fear it could lead to the creation of babies for spare parts.

The 2003 case centered on Raj and Shahana Hashmi, who wanted to conceive a baby with the same tissue type as their 6-year-old son Zain, who suffers from a rare blood disorder.

The anti-abortion group Comment on Reproductive Ethics challenged the decision.

But the Law Lords — judges who sit in the House of Lords — said yesterday that screening to ensure a baby had the same tissue type as Zain could be authorized by Britain's reproductive watchdog, the Human Fertilization and Embryology Authority.

The Hashmi family conceived twice naturally in their attempt to find a tissue match for Zain. They aborted a fetus found to be carrying the same rare blood disorder as their son and gave birth to a child whose tissue was not compatible with Zain's.