General:
* Work
* Toil
* Effort
* Task
* Activity
* Service
Related to employment:
* Employment
* Occupation
* Job
* Profession
* Trade
* Craft
Related to childbirth:
* Childbirth
* Delivery
* Parturition
Other:
* Drudgery (hard, unpleasant work)
* Sweat (physical exertion)
* Grind (hard, monotonous work)
The best synonym for "labor" will depend on the specific situation and the nuance you want to convey.