He was summoned by Lex Luthor to check up on Lana after Clark kidnapped her and took her to his barn. Out of earshot, he informed Lex that Lana's pregnancy was not "typical", but was progressing as scheduled.
When Lana fell down the stairs, he was called again to treat her. Langston assured Lana that the baby was fine. He gave her an injection to sedate her and bring down her blood pressure, assuring her that it would not harm the baby. He suggested Lana be moved to an older wing of the hospital to secure her safety. On Lex's wedding day, Dr. Langston threatened Lex by claiming he would tell Lana everything about her "condition" if Lex didn't deposit two million dollars into his account. In a blind rage, Lex then beat him in the basement of a church until he tripped and fell hitting his head on a stone tomb which he was buried in.
When Lana woke up in Smallville Medical Center after her miscarriage, she asked Lex to call Dr. Langston, but Lex claimed he wasn't answering his pages. Lana wanted answers to explain her miscarriage, but she fell into a deep depression after she learned that Dr. Langston was killed in a car accident on the day of their wedding.
When Lana learned that her pregnancy was a fraud and never existed, she was shocked and confused. Her treating doctor informed her that instead of the prenatal vitamins she was told she was taking, they were actually synthetic hormones that simulate pregnancy. Langston, very likely on Lex's orders, is probably the one who gave them to her.