Questions like, “What if this gives them an excuse to fire me?” and “What if they pass me up for this promotion?” may creep into her mind, despite the explicit laws that protect against pregnancy-related discrimination.

But what if an employer were find out that an employee is pregnant before she’s ready to disclose that information? While that sounds like it should be illegal, it isn’t—and it’s happening right now, according to the Wall Street Journal.

Health care analytics companies can mine workers’ medical claims, pharmacy claims, and search queries to figure out if an employee is trying to conceive or is already pregnant. One such company is Castlight Health CSLT 8.82% , which counts major employers such as Walmart WMT 0.32% and Time Warner TWX 2.15% among its biggest clients.

Castlight has the ability to gather workers’ medical information, then use that data to identify segments of an employee population that are about to make certain decisions, senior product manager Alka Tandon told Fortune. “We can tell who’s at risk for being diagnosed with diabetes, who’s considering pregnancy, who may need back surgery,” she says.

While the company can pinpoint the specific individuals with certain medical needs, it only shares top-level numbers with its clients, says Tandon. For example, Castlight can tell a client that its workforce includes 60 women who are currently trying to have children, but it will not disclose the names of those employees. It also caps the size of any group it will single out at 40 people, since it believes that any smaller group could allow the client to identify the individual employees.

Imposing these rules and minimums makes sense in theory, but realistically does little to prevent companies from knowing who has what medical issue. “You might as well put employees’ pictures on a bulletin board,” says Nicolas Terry, a professor at the Indiana University Robert H. McKinney School of Law, who specializes in studying the intersection of medicine, law, and information technology.

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