ABC News(COEUR D’ALENE, Idaho) — One early morning in 1987, staff at a local hospital in Coeur d’Alene, Idaho, noticed an odd sight: a pregnant woman in labor had checked herself in alone, without any luggage or personal items.She signed in with the name Amy Dee Beach, claiming she was single and unemployed. She said she was from California and had been visiting friends in Idaho.At 6:30 a.m., she gave birth to a healthy, full-term baby girl.But after a short time with her new baby, the mom did something inexplicable.“She disappeared 12 hours later. She just left the hospital gown on the bed and that was it,” genetic genealogist CeCe Moore told ABC News’ “20/20.”Mystified, the nurses gave the abandoned baby girl a nickname: “Baby Girl Beach.”Baby Girl Beach was later adopted by the Klugs, a couple from Idaho, who was unable to have children.The family named her Andrea. She grew up enjoying playing the piano, swimming and gymnastics.“This was, you know, such a dream that we had had for so long. When they brought her out, here came this beautiful, beautiful little girl,” Beverly Klug, Andrea’s adoptive mother, told “20/20.”Today, Baby Girl Beach is now Andrea Klug-Napier, a 31-year-old medical office manager living in Colorado.Klug-Napier knew she was adopted from an early age. But she had no idea of the strange circumstances around her birth until age 16, when her adoptive parents finally told her.“They told me I was abandoned at the hospital, and I could not believe it,” Klug-Napier told “20/20.” “This story is crazy.”Klug-Napier, who has a tattoo with the words “Baby Girl Beach,” says the mystery of her birth was one she felt compelled to solve.“There’s always going to be a void that you don’t know about. I just have always wanted to meet whoever she was,” Klug-Napier said. “I just wanted to look like somebody. I just thought that I would never really know.”Klug-Napier then embarked on a quest to find her birth mother and turned to social media for help. She posted a photo of herself on Facebook holding a sign outlining her story. The post went viral.Klug-Napier connected with genetic genealogist CeCe Moore, who aided her in her search, and the two started with the hospital she was abandoned at.Kim Beckman, a nurse at the hospital who cared for Klug-Napier, remembered trying to fill the void left by the baby’s vanished mom.“I remember holding you a lot — I worked evenings — and rocking you and wanting you to feel loved,” Beckman told Klug-Napier.One clue was an admission form left at the hospital by Klug-Napier’s mother, and on it, next to Andrea’s baby footprints was her mother’s fingerprint.The two enlisted the help of the Post Falls Police Department to search their database for the fingerprint; however, they didn’t find anything in the system associated with the fingerprint.By using a sample of Klug-Napier’s DNA, Moore was able to find a startling match with someone in a DNA database. Moore learned that Klug-Napier had multiple siblings and that they all shared the same mother and father.“I thought, ‘Wow, this actually worked. I found something. I just couldn’t even get on a plane fast enough to go meet her,” Klug-Napier said.ABC NewsKlug-Napier wasted no time and headed from Colorado to Wisconsin to meet her newly-found biological sister Heather.“I was so nervous for her to open the door. I just didn’t know what to expect,” Klug-Napier said. “She opened the door, and there was Heather.”At first, the meeting between Klug-Napier and her sister Heather was awkward.“I just knew immediately that we were both really shy and kind of awkward, and she just immediately told me that she had a bunch of information about our biological family,” Klug-Napier said.Heather was adopted in Oregon, a state which allows sealed records to be opened. She told Klug-Napier she knew the names of their birth mother and father.“Our birth mom’s name is Deirdre. She went by Cindy,” Heather told Klug-Napier. “Our dad’s name is Dwight.”Heather also revealed that their mother had a baby boy two years after Klug-Napier was born and that she and the baby both died.“When I heard that news, I just … I just came to a stop,” Klug-Napier said. “I will never be able to meet her.”She continued, “All this time I thought maybe somebody was thinking about me and where I was, but she hadn’t. It feels like I just lost somebody and that I didn’t even know.”And while Klug-Napier and Heather were deserted, their mother and father raised two sons.The sisters next made a trip to meet their two brothers and their 64-year-old biological father Dwight in Spokane, Washington.“I can’t even describe the feeling. It was crazy,” Andrea said. “Dwight immediately started talking to us and telling us everything that he knew about our mother.”Cindy was only 16 years old when she married Dwight, then 17. She later worked as a computer programmer. Dwight told them about the day she died.“It was 20 below here. Weather was bad. The city was shut down, and she told me she had the flu,” Dwight said.Dwight said he left for work and when he returned home, his wife was unconscious. They took her to the hospital, where she was pronounced dead.“The doctor said was that she was really torn up inside. It wasn’t ‘til I went home and it was a couple days later, I went to the bedroom. Doors were locked. You know, I went in there, and there was a baby on the bed,” Dwight said. “Full-term baby.”Dwight lost both his wife and son at the same time and didn’t even know he had fathered the baby boy.“I thought I knew her, I thought everything was great,” Dwight said.He said he also had no idea that his wife had given birth to Klug-Napier or to Heather.“I thought at first I’m for sure going to see something in Dwight, that maybe he did know and he’s hiding it from us,” Klug-Napier said. “But immediately when we sat down he started talking. I knew that there was absolutely no way that he knew about us.”Dwight said his wife had hidden the pregnancies from him and when she was pregnant with their sons Aaron and Dennis, she barely showed.“Her stomach wasn’t big at all. It was, just seemed like she gained a little weight around the face,” he said. “I still question it myself today, wondering how did I miss it.”On Cindy’s death certificate is a strange saying: “Unattended birth associated with psychotic denial.”“Denial of pregnancy is a recognized psychiatric or psychological condition,” psychiatrist Susan Hatters-Friedman told “20/20.”Hatters-Friedman has studied the disorder and says it’s surprisingly common: 1 in 400 women may suffer from some form.“The woman may have some idea that she’s pregnant intellectually, but she pushes it from her mind until she can no longer do so because she’s suddenly giving birth,” Hatters-Friedman said. “She may not have such significant weight gain that others notice, or she may have already been heavy. And others aren’t noticing the change.”“A young woman’s own experiences of abandonment could contribute to denial of pregnancy,” she added.Behind Cindy’s odd behavior is a painful backstory, according to Heather. As a small child, Cindy and her sister were both given up for adoption. They were on a bus together but at the last minute their brother pulled Cindy’s sister off and left Cindy on the bus alone.“We only can speculate what story of emotional damage that may have done to Cindy very early on in her life,” said Moore.In the journey to finding her biological family, Klug-Napier met a fourth sibling, her 32-year-old sister Marysia. She traveled to Washington to meet her.Like Klug-Napier, Cindy arrived at a hospital in Spokane, Washington, gave birth and disappeared hours later, leaving newborn Marysia behind. Cindy used the alias “Sandy Davis.”Upon meeting, the two sisters marveled at their similar stories.ABC News“Looking at her was so surreal, to see these features that I see in myself every day,” Marysia told “20/20.” “I think Andrea and I did have a connection when we first saw each other. We’re both hesitant and a little bit shy, and I think that actually, you know, helps us kind of understand each other a little bit more.”And in another stunning find, Klug-Napier learned she had a fifth sibling, a 35-year-old brother that Cindy gave birth to and abandoned at a hospital and another child that Dwight never knew he fathered.“I just couldn’t — didn’t know she was pregnant. Couldn’t tell,” Dwight said.Dwight said he sees all of them as his children.“It was kind of a happy feeling because a part of Cindy was coming back,” he said.Watch the full story on ABC News’ “20/20” this FRIDAY at 10 p.m. ET.Copyright © 2018, ABC Radio. All rights reserved.