U.S. employers above a certain size are required by the Family and Medical Leave Act (FMLA) to provide some unpaid maternity/medical leave. Small employers (such as where my wife works) are exempt from any requirement, and it varies according to the employer and what the job market requires (i.e. not much for most fields). Also, part-time workers receive absolutely zero protection.
The United States is incredibly backward in this regard (among many others). Combined with our lack of support for childcare (tax breaks are meaningless when you're not making enough money), it's no wonder that we're well behind most of the rest of the world when it comes to workforce participation rates for women.
In my experience, most white-collar jobs tend to provide two weeks of paid vacation, a week or so of personal/sick days, and—if they're generous—some [mp]aternity leave (I get one week at my current job). Due to the labor market, tech jobs tend to be more generous, but even the most generous policies by US standards tend to fall short of the minimum required policies in more enlightened nations.
Many companies do provide maternity leave, many (but fewer) also provide paternity leave, but companies below a certain size are not federally required to provide either (though I believe there are some arrangements where you can take unpaid maternity leave but legally can't be fired during your maternity leave).
It makes a bit of a joke of gender equality in the workplace, IMHO.