Mitt Romney brood grows, twin grandchildren born using surrogate

Mitt Romney is a grandfather again, and he has a surrogate to thank.

Tagg Romney, the presumptive Republican presidential nominee's oldest son, announced Friday that he has newborn twin sons. Tagg Romney tweeted "big thanks" to the surrogate who gave birth to the twins. David Mitt and William Ryder were born on Friday.

The two additions mean Mitt Romney and his wife, Ann, now have 18 grandchildren. They range in age from 16 to now just a few days old..

Ann Romney tweeted her congratulations. "Grandchildren 17 and 18 are here," she wrote on Twitter. "We can't wait to meet David and William."

Tagg, 42, and his wife, Jen, 39, have appeared on the campaign trail with the former Massachusetts governor, sometimes with their four other children. This is the second time the couple has used a surrogate. Their son Jonathan was born in 2010 via a surrogate.

Tagg Romney spoke with the Mormon Church about his family's plans before the children were born, a campaign aide said. Michael Purdy, a spokesman for the LDS Church, said, the church discourages surrogate motherhood but leaves the decision to individual members.

There is some opposition to surrogacy among social conservatives. The in-vitro fertilization that's required can cause the destruction of embryos, a problem for some anti-abortion groups.