More than one in five babies born in Brighton and Hove last year were born to a non-UK mother.
The city reflected a trend across the county which has seen the number of babies born to mothers from outside the UK rise at a much higher rate than the overall population increase.
Crawley has the highest percentage with more than a third of new mothers in 2011 from outside the UK while Rother and Adur had the lowest percentage with around one in ten.
Nearly 3,500 babies in Sussex were born to non-UK mothers in 2011 – an increase of 5% on 2010.
The overall increase in the total number of births in the county over the same period was only 1%.
There were 43 more births from non-UK mothers in Brighton and Hove last year compared to 2010.
Of the 3,291 births in the city in 2011, 323 mothers came from the EU, 227 from the Middle East and Asia and 145 from Africa.
MP Henry Smith said that one of the factors in Crawley’s higher number of non-UK mothers was expectant mothers arriving through major airports like Gatwick to access British maternity skills.
The MP is seeking to introduce a bill instructing NHS trusts to record and audit the cost of treatment of non-UK residents and individuals not entitled to free health care.
Figures uncovered by the Crawley MP from the UK Border Agency revealed that on average 150 heavily pregnant mothers due to give birth in a matter of days passed through Gatwick Airport every year.
He said that while immigration helped to fill the skills gap in sectors like the NHS, the level of immigration also put extra strain on health services and schools.
He added: “Schooling is an issue with quite a lot of schools in Crawley having to hastily add extra classrooms and a lot of that is to do with high levels of immigration over a short amount of time.
“The problem is the uncontrolled immigration we have seen in the last decade.”
Hove MP Mike Weatherley said: “Where there is a willingness to be a good neighbour and a desire to work hard, I am more than happy.
“That’s what we see from the majority of residents in Brighton and Hove who have come from abroad.”