Police believe the baby found in the Constance Marten and Mark Gordon investigation "may have been dead for some time" and they have been unable to confirm its gender.
Detective Superintendent Lewis Basford of the Metropolitan Police Service said:
"At this stage we have not yet been able to confirm the baby's gender and a post-mortem examination has not yet taken place.
"Despite this, based on the inquiries we've carried out so far, we believe, sadly, the baby had been dead for several weeks before they were found. It's too early for us to provide a more specific date."
He adds that the case has been referred to the police watchdog.
Police say Constance Marten and Mark Gordon remain in custody and the warrant for further detention granted on Wednesday lasts until Thursday evening.
Event Bookings Go Live For Worthing Festival ‘24
Man Charged After Throwing Brick Through Brighton Restaurant Window
Peacehaven Man Disqualified Over High-Speed A27 Pursuit Near Brighton
Appeal After PCSO Assaulted In Uckfield
Man Charged With Rape Of Teenage Girl In Newhaven
Overnight Closures For A22 Forest Row Road Improvements
Brighton Defence Manufacturer's Controversial Planning Application Likely To Be Heard
Over £2.4m Approved For Worthing School Support Centre
Section Of M25 To Close Again Tonight - As Drivers Warned Not To Get Complacent
Plans For 800 New Horsham Homes Refused