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10 men and three women - aged between 24 and 57 were arrested on Wednesday in Rochdale, Failsworth and Cheetham Hill.
They're being held on suspicion of a range of offences including trafficking people for exploitation, conspiracy to facilitate breach of immigration law, conspiracy to assist unlawful immigration into a member state.
Three people were arrested over being overstayers in the UK.
The pregnant victim was forced into marrying a man in July in Rochdale. She'd come to England two months earlier thinking she was visitng her sister in Luton.
Police say a man who met her at the airport purporting to be her sister's friend was paid between £10,000 and £15,000 by the trafficking gang to arrange the sham marriage.
The victim, who was 25 weeks pregnant when she arrived in the UK in May, later raised the alarm at a hospital where she had been taken to have an abortion.
Detective Inspector James Faulkner said: ``This is a superb result following a long and complex investigation by GMP officers and our partner organisations.
``This woman was brought to Manchester with the sole purpose of being married to a man who hoped to boost his immigration status.
``She was completely unaware of this group's nefarious motives and by the time she realised what was going on, it was too late.''
Mr Faulkner said there are currently as many as 400 cases involving women being trafficked for sham marriages in the Manchester area.
He said: ``That is 400 women who were brought to this country on a false premise and trapped in relationships with men they do not know, 400 women enslaved by gangs only out to make money from their predicament.
``On top of that, Home Office statistics place a cost of £40,000 on the UK economy for each sham marriage.
``That is a potential cost of £16 million to the city of Manchester in benefits, police and council resources and other costs, a gigantic sum especially when you consider the budget cuts affecting every single household in Greater Manchester at the moment.