A garda search on the river Barrow is being wound down for the night as the investigation into the disappearance of Aoife Phelan continues.
Divers spent over four hours searching the waterway under the M7 motorway and downstream from there, but nothing has been found so far.
The M7 was closed for a time as gardaí carried out a ground search between Monasterevin and Portlaoise but was later reopened.
Ms Phelan was four months pregnant when she went missing from a friend's home in Portlaoise 12 days ago.
Gardaí believe she has been murdered.
Detectives searched a house on the Timahoe Road overnight and excavated adjoining land.
A 24-year-old man is being questioned at Portlaoise Garda Station in connection with the investigation.
It is understood he is known to Ms Phelan and from the local community.