A gay Israeli couple discovered Wednesday that the newborn baby they received after completing a surrogacy process in Nepal is not genetically their child.

The baby did not come from egg fertilized by sperm that the couple had provided, Ynet reported.

The Israeli surrogacy agency Tamuz, which organized the process for the couple, said the mistake was a rare case of “human error,” according to the Haaretz daily.

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The couple flew to Nepal last month to await the birth of their child, and cared for the newborn girl for several weeks while awaiting the results of routine genetic tests. The mistake was discovered in the course of the tests conducted at the Sheba Medical Center in Tel Hashomer Hospital, Haaretz said.

All Israeli parents of overseas surrogate births undergo the tests to prove that the children are actually theirs. It is only when the results are returned, after several weeks, that the parents can formalize the status of their babies.

The couple had to hand the baby girl over to its biological parents, who were waiting to get their own surrogate child at the same hospital. They are now waiting for a second surrogate mother to give birth, to see whether the sperm they provided was used in the fertilization of that child.

Tamuz, which has operated over recent years in the Far East, the US and Mexico — guiding parents through the process and providing them with psychological support — said the rare human error took place in a laboratory in Nepal.

Commenting on the case, the owner of a separate and unconnected surrogacy agency in Israel said she was sure mix-ups happened in cases of fertility treatments within Israel, but that “there’s no need for genetic testing, so it can’t be proven.”

Dana Magdassi, owner of the Lotus agency, which has also worked in Nepal, told Haaretz: “It’s a very serious human error, but it doesn’t only happen overseas. I think it happens much less overseas, because the doctors know that at the end of the process, it’s obligatory to do a genetic test, so they’re doubly careful.

Israel’s first surrogacy law came on the books in 1996, and it has not been amended since then. Only heterosexual couples are legally able to use surrogacy in Israel, and there are many restrictions on who can serve as a surrogate. While straight couples must go through an onerous committee process in order to qualify for surrogacy, homosexual couples are left completely out of the system. Consequently, they must look to foreign surrogacy.

In August 2015, Nepal ordered a halt to commercial surrogacy services in the Himalayan nation until it rules on the legality of the practice.