In general, it's always a good idea to ask if the colleague wishes you to keep in touch with them whilst they are on maternity leave or encourage them to stay in contact with you. You should keep them informed of issues which may affect them. For example, you should keep them informed of any relevant promotion opportunities or job vacancies, company news that arise during their maternity leave. It can also help you both to prepare for your employee's return to work as they will feel that they have no been 'out of the loop' for too long. However, if the colleague does not want to be contacted, you must respect this as this is a period of statutory leave protected by the Maternity Act, 1994 and the Maternity Protection (Amendment) Act, 2004. 

The leave can be taken at any time in the 26 weeks' following the birth of the child (or placement in the case of adoption). 4 weeks' notice is required before the leave may be taken however there is provision for shorter notice. The legislation allows for the postponement of leave in certain circumstances, such as the sickness of a relevant parent and hospitalisation of the child. relevant information in relation to application is available through this link https://www.gov.ie/en/service/apply-for-paternity-benefit/