"'So we asked the girls what they thought about having another addition to the family and they really wanted it."
In December 2009, the couple returned to Midland Fertility Clinic for another cycle of IVF, using the 10-year-old embryos. Ryleigh arrived in November.
"The girls are thrilled to have a sister -- and they know that she was conceived at the same time that they were, but has been in the freezer," said Lisa Shepherd.
Doctors say there are few safety concerns about using long-frozen embryos.
"Once an embryo is frozen, it's essentially frozen in time," said Dr. Jani Jenson, a reproductive endocrinologist at the Mayo Clinic. "As a group, children born with IVF are one of the most scrutinized cohorts. "
Because these technologies are only 40 years old, no one knows how these babies will age, but all other studies have indicated IVF is safe.
"The data we know from fresh and frozen transfers are that it doesn't put them at any unique or known risks like learning disabilities or birth defects," said Jensen.
The Shepherd case is, "interesting, and yet mundane," said Dr. Ellen Clayton, director of the Center for Biomedical Ethics and Society at Vanderbilt University. "They are just siblings and this is clearly a family where everyone resembles everyone else. The twins look like two peas out of a pod and this is the third pea."
Ethical concerns have been raised about risks involving IVF, according to Clayton, but the "relevant metric" is how parents make other choices about having children.
"The current thinking is that parents are free to make pretty broad choices," she said. "They are free to continue a pregnancy with Down syndrome. People make all kinds of choices that are potentially risky."
As for the Shepherds, said Clayton, "God bless them. This looks like a happy family that is now even happier."