Gases that contribute to the greenhouse effect include: 1  Water vapor. 2  Carbon dioxide (CO 2). 3  Methane. 4  Nitrous oxide. 5  Chlorofluorocarbons (CFCs).
You can start maternity leave any time from 11 weeks before the beginning of the week your baby's due. You can bring the date forward if you need to take time off work for pregnancy-related reasons within four weeks of the expected birth date. Your employer may make you start your leave from then.
For example, if you were due to return to work after 52 weeks' maternity leave on 1 August, but then decided to return to work after 39 weeks of leave (that is, on 9 May) you would need to give eight weeks' notice of the new date (that is, by 14 March).