OK, READ THIS!!
“Veronica met Peter in Yale Law School, though she always told her children they met at Martha’s Vineyard. She was intending to practice law herself, but she found out she was pregnant with Melissa just after her first year of graduate school. Peter’s mother demanded they get married, and Veronica never did get to go back to law school again, though it was her initial intention. She could not get pregnant again because she would be risking her health, due to complications from Melissa’s birth, so she and Peter found a surrogate named Olivia Caldwell to carry Spencer to term for them. Though Spencer shares some physical similarities with Olivia, most notably their green eyes, she is still the biological child of Veronica since she supplied her egg to Olivia”
In the PLL books Spencer was born through surrogacy, NOT by Veronica Hastings.. If this is the case, then someone else could be Spencer´s parents! :O