The hospital was taken off special measures in 2006
An inquiry is under way at a hospital maternity unit where 10 women died after three more deaths were reported within the last 10 months.
Northwick Park Hospital had been placed under special measures after the previous deaths between 2002 and 2005.
However, in September 2006, the Healthcare Commission praised the hospital, saying services had "improved significantly".
North West London Hospitals NHS Trust said procedures were under review.
The latest death was in the unit was on 20 March and is currently being investigated, the hospital said.
However, the hospital refused to divulge details about the causes or dates of the other two deaths, citing patient confidentiality.
Fiona Wise, chief executive of The North West London Hospitals NHS Trust, said: "Given that it has been 18 months since we were lifted off special measures, we feel that it is the right time to undertake a review to re-check our systems and procedures.
"This also gives us the opportunity to review again the three maternal deaths that the trust had during 2007 and 2008.
"Two of the maternal deaths have been investigated on an individual basis and there is currently no evidence to show that there were any issues with the quality of care received in these cases."
Ms Wise said that the review would "reassure" the hospital that "there is no common link" between the recent deaths and to check whether the staff did everything possible to prevent the deaths.
The hospital said it had invested £19m in improving facilities and increasing staffing levels.
A Healthcare Commission spokeswoman said they are aware of the latest deaths.
She said: "We have discussed this with the trust, including their plans to undertake a formal review. At this stage, we are satisfied that the appropriate action is being taken by the trust.
"But we will of course keep a close eye on this matter."
Following the 10 previous deaths, a report by the commission said the hospital lacked resources to deal with high-risk cases and there were too few consultant obstetricians, midwives and dedicated theatre staff.
It had also criticised the level of care in nine out of 10 cases.
Catherine Murphy, director of communications of the Patients' Association, said: "We would hope that the trust would not put patients' safety at risk and that they had adequate resources and appropriate skills mix of staff available at all times.
"We hope the trust is doing everything to allay fears of pregnant women who may be booked into this unit."
A maternal death has been described as the death of a mother during pregnancy or within 42 days of delivery.
The internal review, which will also look at external clinical input, will be completed by the end of May, the trust said.