In 2001, Maryann DeSimone had just about given up hope that she would be a mother.

After two failed attempts at in vitro fertilization, she and her husband Robert were thinking about other ways to enrich their lives — extra vacations, maybe even buying a boat.

“I just knew it wasn’t in the cards,” said DeSimone, who lives in Huntington, N.Y. “I wasn’t open to adoption at that point, I thought, ‘I’m not supposed to be a mom or give birth.’”

Meanwhile, in Ukraine, three girls — Katia, 9; Darya, 7; and Irina, 6 — were in need of a family.

Raised on a farm, the girls’ mother had died in childbirth and their father, in his grief, had become an alcoholic. The government had taken custody of the children and placed them in an orphanage.

Katia, Darya and Irina needed a home, and the DeSimones needed children.

VIDEO: Click here to watch more about the DeSimones' story

The adoption process started in late 2003 and became official in January 2005. It wasn't easy. In order to get paperwork filled out, everyone in Ukraine (clerks, notaries, even police officers) had to be gifted or incented for their cooperation. And of course, they had to hire a translator, who would prove to be helpful later on.

Everything seemed to be going smoothly — the girls were transitioning well, learning English and enjoying family vacations.

Until one day at the dinner table, Darya — the middle child — blurted out, “Please find Vera. When Mommy went to heaven, Vera never came home.”

Vera is the baby that the girls’ mother died giving birth to. Today, she’d be 9-years-old. Knowing their daughters had a sister somewhere in the world, the DeSimones immediately started a search. But at times, it's like looking for a needle in a haystack.

“If she’s available, we would take her immediately,” said Robert DeSimone. “If she’s with a family, we want to give the girls closure — anyway they can have her in their lives.”

Working with the translator in Ukraine, the DeSimones have deduced that Vera could have been adopted by another family, in which case she most likely was sold on the black market, or she could still remain in Ukraine’s orphanage system.

The DeSimones know their daughters’ birth name is Segeda, but there is a chance Vera’s name and birth date have been changed.

“These children can be very well-hidden,” Robert DeSimone said. "We were informed that back in the year 2000, in the Russian Republic, organized elements of crime had pilfered children in order to get in the baby adoption business. This was a lucrative industry."

They have found some birth certificates that bear the girl’s name, but the spellings were different. The DeSimones’ translator in Ukraine also found a nurse and hospital administrator who were there the day Vera was born, but they were unwilling to talk.

The DeSimones realize their daughters’ missing sister has most likely been adopted, perhaps in Italy or Germany, where many Ukrainian babies end up, but that hasn’t stopped them from searching.

“We need support in being able to find documentation where she is,” Robert DeSimone said. “Whether she’s in the system, or with family. We’d love a conversation with the girls’ (biological) father. Is there a way to meet with him? We’re sure he knows some missing pieces.”

The search is costly — in order to get information from Ukrainian officials, the DeSimones had to return to gifting and incenting, which they did when they adopted the girls. They admit they have also sent money to the girls' biological father, in order to help him out, although he has not responded or showed any interest in the girls' welfare.

No matter what, the DeSimones refuse to give up.

“The girls have saved clothes for her, opened a bank account for her. … They want to buy her birthday presents,” Robert DeSimone said.

And if the search doesn’t lead anywhere, the DeSimones will keep telling their story of how they found three beautiful daughters.

“There may be other adoptive parents out there who could benefit from the story,” Robert DeSimone said.