EXCLUSIVE: For couples who seek reproductive help, an IVF mixup and its emotional implications is one of their worst nightmares. HBO Max is tapping into that with a series in development that comes from the This Is Us duo of Mandy Moore and Julia Brownell . Moore is executive producing the untitled project, written and executive produced by Brownell, who will serve as showrunner. While Moore does not have an acting deal in place, she is expected to star if the drama is greenlighted as a limited series, I hear. The untitled IVF project tells the story of two families coming together against incredible odds and discovering a newfound extended family that they never could have imagined. The role of one of the parents is intended for Moore, sources said.…