Northwick Park Hospital's maternity unit serving Harrow and Brent has seen a mysterious downturn in admissions.
The North West London Hospitals Trust is investigating why women who are booked into its birth unit at Northwick Park Hospital by their GPs are failing to show up, according to a report to the trust's governors.
The maternity unit has been criticised in the past for a high mortality rate and difficulties recruiting staff.
But the trust has had some success filling vacancies in the past month.
The report said 20 midwives and two consultants had been recruited, leaving 22 midwifery posts remaining to be filled.
Northwick Park Hospital and the Central Middlesex Hospital's A&E have both seen large rises in the number of admissions.
Admissions rose seven per cent over the past eight weeks compared with the two months before that, putting frontline staff under extra pressure.