After WW2 The pressure on pregnant teenage girls to give up the baby for adoption, mostly came from her own family who refused to let her bring it home because illegitimate babies/little bastards were a social disgrace.
We lived next door to a "Mother and baby home"... the place parents sent their daughter to live in while pregnant so nobody suspected. Then if she gave the baby up for adoption she could return home with a flat belly some cover story like "glandular fever" to explain a long absence from school/ family home.
Single mothers could decide to keep their baby, apply for a place in council day care, and go back to work.
That's what my long-widowed single Mother did (1962) when she accidentally got pregnant during a long distance affair with a married man. It was a five minute wonder to gossip mongers as her work persona was very well known . She cheerfully brazened it out.
7 years later in 1969 my sister 17 left home , got a job in London. Got pregnant ( no idea which guy) ; told SS to arrange adoption; changed her mind as soon as she gave birth. SS changed gear. Put the baby in temporary foster care until they had found Sis a live-in job with a flat; council day care for baby; she collected the baby at 6 weeks and never looked back.
She went back to college, trained, became a teacher, raised her daughter, bought a house, all on her own.
Those are just two of the many unmarried mothers I knew in the 1960s /70s.
There was no state coercion to have the baby adopted.. There was social pressure from disapproving family. If anything, it was State support and provision which enabled and supported many single girls who wanted, to keep their child, find an affordable home and day care.
ASince my father died, I'd been the child of a single parent, before I watched my Mother and sister both get pregnant with an unplanned child and bring it up alone
I made damn sure that never happened to me or my children.