Not so long ago, according to one Dr Alan Guttmacher, doctors used the word “monsters” as a quasi-medical term, handed down from an 18th-century midwives’ manual, for conjoined twins. Guttmacher was head of gynaecology at Mt Sinai, the hospital where the twin gynaecologists whose story was the inspiration for Dead Ringers briefly worked together. As a twin himself, he held firm views on the supposedly unhealthy psychology of the twin bond. “All separate identical twins may be regarded as monsters who have successfully escaped the various stages of monstrosity,” Guttmacher wrote in one of his many papers on the subject. In a way, he believed, identical twins who had separated in the womb were more at risk of being conjoined psychologically. At least conjoined twins had distinct identities, since they could not be mistaken for each other.

David Cronenberg’s Dead Ringers, a 1988 film starring Jeremy Irons as twin gynaecologists called the Mantle twins, recycled many real-life details from the case of Stewart and Cyril Marcus, celebrity twin New York fertility experts whose lives collapsed into a morass of drug addiction, squalor and madness before they both died, one a few weeks after the other, in 1975.

Aspects of the Marcus case – the fact that they both chose to specialise in gynaecology, the balance of power between smooth operator Stewart and back-room plodder Cyril, the years of drug sprees, their final bacchanale combining Nembutal with children’s party food – were seamlessly threaded between Cronenberg’s usual concerns of body horror, altered states of consciousness, the coercive nature of institutions and the blurring of sex and power.

Elliot, the dominant brother in his film, sets up and tries out sexual partners before passing them on to the more reticent Beverly, each pretending to be the other as circumstances demand. It’s just a game, until they encounter perceptive actress Claire Niveau (Genevieve Bujold). Obsessed with Claire, Beverly feeds his addled energies into designing a range of hooked and pointed instruments “for use on mutant women” that nobody who saw the film will ever recall without wincing. Along with its many other fixations, Cronenberg’s film twists a scalpel in the belly of misogyny.

It thus comes as something of a surprise to see a new version of Dead Ringers in which the twins are women, still called Elliot and Beverly, but now both played by British actor Rachel Weisz. According to chief writer Alice Birch, who has previously won an Emmy for her script for Normal People and a WGA award for her work on Succession, the gender swap “changes everything, but it also changes nothing”. Rachel Weisz, who brought the idea to Birch, says she was always fascinated by the co-dependency of the Mantle twins “who do everything together, who live together and work together but are then pushed apart by the patient who comes between them,” she says. “I thought, ‘oh God, wouldn’t that be an interesting story to tell?’ And so I could be in it, I thought it could be women.”

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In fact, the characters have evolved to be quite different from the male Mantle twins. “The first decision was that they were going to be obstetricians, not just fertility doctors, so they were going to be bringing babies into the world, so that changes things radically,” says Birch. “That was a story decision, feeling we’ve got six hours and were hungry to tell new stories.”

But the contrast between the two characters is also much sharper than it was in Cronenberg’s film – if they weren’t twins, they wouldn’t like each other at all – which is reflected in their professional interests. Elliot, the drug fiend and party girl, is a driven innovator playing Frankenstein with jars of tissue and foetuses in her futuristic laboratory; Beverly wants to revolutionise the way women give birth, to make it safer and more humane; Elliot calls her Miss Goody Two-Shoes, while also doing her best to help her become pregnant. Insemination is just one of their shared activities, however; they have never so much as spent one night in different cities. Until, as in Cronenberg’s film, Beverly falls in love with a patient Elliot has seduced for her: an actress called Genevieve (a homage to Bujold) played by Britne Oldford. It is the first threat to the twin dyad. Elliot fights back. Beverly swings between the two of them.