How about something like this:
When it comes to signing time for women (as only they can become pregnant) there are two basic contract types offered.

The first is your standard equal pay for equal work type, but the employee agrees not to get pregnant during the term of the contract. This assures the company that they won't lose a valuable employee, have to pay out wages and benefits for someone who isn't there, and all of the costs for getting a temp and training them, et cetera. As primates with brains, we have a certain amount of control over reproduction.

The second contract has the employee agree to accept a lower grade of pay for leaving open the option to get pregnant during the contract's duration. The difference between the standard and lower pay will be the company's estimated cost of loss of productivity and finding a replacement, et cetera. Note that the employee is not required to be or become pregnant during this time, she is just reserving the option.

If someone on the first type of contract is pregnant at the time or becomes pregnant, then apply whatever litigation is appropriate in your area for breach of contract.

Five percent of the employees where I work were off on maternity leave last year, and productivity took it on the chin. Taking some sort of responsibility seems reasonable.
(Ejaculantern was caught desecrating pumpkins on, Tue 5 Jan 2010, 6:13, Reply)