Conception, pregnancy and childbirth are defining human experiences, and so remain perennial themes for horror, from Rosemary’s Baby to the Alien franchise to Prevenge. Occupying a no-woman’s-land between life and death, they’re innately anxiety-inducing, perhaps making it harder for film-makers to supply a truly individual take. Debut director Raymond Creamer comes close by initially digging into the interpersonal dynamics around the home-birthing pool of a headstrong mother-to-be, before he defaults into a schlocky creature feature.

Goody (Samantha Robinson) is in the pool, ready for battle, soaking in good vibes beamed at her by husband Jayson (Colby Hollman), his doula sister Candace (Zoe Renee) and their rock, midwife Sarah (Colleen Foy). But shaken by weirdly spaced contractions, Sarah takes Jason aside and admits that she has a bad feeling. It’s not purely premonition: a flashback reveals, in contrast to the new-age love-in around the tub, Goody’s insistence against Sarah’s advice that she give birth in winter at their forest cabin. The midwife fears it will make going to hospital too difficult should anything go wrong – and only agrees to supervise because Goody will probably go ahead solo if she pulls out.

Creamer starts out by layering telling details that insinuate the stifling boho perfectionism ruling this household: a faux Freewheelin’ Bob Dylan cover featuring the couple, their disdain for teabags, the cloying veneer of positivity. He films the damning flashback with psychological finesse to show Jayson’s status as junior partner; back on the natal frontline, Candace sometimes slips into a grandstanding bolshiness that threatens to tip Sarah’s carefully nurtured equilibrium out of balance.

Given this careful familial setup, it’s a bit bewildering when the film takes a sudden demonic swerve. What was initially an exercise in cannily undermining Goody’s (and the audience’s) need for an authority figure turns into a hurdy-gurdy occult blowout. As Goody starts raving about Asmodeus, Sarah lurches between panic and calm in a manner that feels increasingly nonsensical. (It’s probably fair enough, though, when she’s being dragged underwater by greasy tentacles.) Jayson’s disappearance is left unexplained and not in a productively disturbing way.

Amid the mayhem, Creamer still manages the odd visual flourish, including Candace’s final esoteric vision. But if Goody Goody really had to take The Omen route, he needed to deliver the transition with far more delicacy.

• Goody Goody is on Shudder and AMC+ from 18 September.