Aisha Chithira, 32, died after travelling to England from Ireland to have a termination at a Marie Stopes clinic in Ealing, west London, on January 21, 2012.
A doctor and two nurses were initially accused of manslaughter by gross negligence and a health and safety charge.
But after a review, the case against Dr Adedayo Adedeji was dropped and the decision taken to only go ahead with health and safety charges against Margaret Miller, 55, and Gemma Pullen, 32.
The pair were due to go on trial at the Old Bailey last week but after days of legal argument, prosecutor Sally O’Neill QC offered no evidence against the women.
They were formally acquitted of failing to take reasonable care of the health and safety of the Malawian woman contrary to the Health and Safety at Work Act 1974.
Members of Ms Chithira’s grieving family were in court as the decision of the Crown Prosecution Service was announced.
Judge Nicholas Cooke QC immediately demanded a review into what “went wrong” in the CPS decision-making process, saying: “What has occurred must not be brushed under the table.”
He said what happened was “not satisfactory” given the delay in the case which had been brought at considerable “time and money”.
He said: “The situation that arose is most regrettable given there was a tragic death.
“What flowed from that was an enormously long period of stress and uncertainty for the bereaved family and likewise for entirely different reasons for the defendants.”
However, he praised the conduct of the prosecution barristers in court.
Dr Adedeji, 63, of Hornchurch, Essex, Ms Miller, from Camberley, Surrey, and Ms Pullen from Stoke-on-Trent, had denied wrongdoing.
Genevieve Edwards, director of policy at Marie Stopes UK, said: “This was a desperately sad case, and our thoughts remain with Ms Chithira’s family. It has taken four and a half years to reach this point, which has been difficult for everyone involved.
“Our charity provides reproductive and sexual healthcare services to 70,000 women a year in the UK, and we are committed to providing the highest level of care.”
Ms Miller’s solicitor Jenny Wiltshire, of Hickman and Rose, said: “The defence has always argued that this case should never have been prosecuted.
“Following six days of legal argument, the Crown Prosecution Service accepted it no longer had confidence in its own decision-making processes. It is hard to think of a more woeful state of affairs.”
Ms Miller had been a nurse of 36 years while her colleague Ms Pullen was also an experienced nurse at the time Ms Chithira came to the clinic for a late stage termination.
She died after being discharged, allegedly from an injury sustained during the surgery.
Manslaughter charges were dropped after expert evidence served by the defence last month found staff had done nothing wrong.
A jury inquest into Ms Chithira’s death is now expected to take place.