The drama from the Yorkshire-born writer behind Band of Gold and The Syndicate, charts the lives of six couples who attend the same parenting craft class; focusing on the various dilemmas faced by both the expectant mums and their partners.
Rollem Productions, the Leeds-based production company set up by Mellor in 2000, will again handle production.
Series 1 launched with an overnight audience of 3.9m viewers (19.1%) on 5 August and enjoyed a steady growth in popularity, concluding with 4.7m (22.8%) last week.
The drama was recommissioned by Controller of BBC One, Charlotte Moore and BBC Drama’s Ben Stephenson.
Mellor, whose production company is behind In The Club, said she had been inspired to write the series by her own experiences with motherhood, initially saying:
“Having given birth as a teenager I know how life changing it is. Birth is the ultimate creation; it changes you and your relationships forever. I’m still close friends with the people I met at my antenatal class.
“I’m delighted to be writing for BBC One again. Both Ben Stephenson and Polly Hill instinctively understand my work. They encourage and trust me to deliver; as a dramatist you couldn’t ask for anything more and for that I’m eternally grateful.”
Series two will also be a six-episode run, however a transmission timeframe is yet to be confirmed.