In the early 1970s, Yvonne Braithwaite Burke was the first member of Congress to be granted this. What was she granted?

Maternity leave!

Good job, SR! While the site linked to below doesn't say that she was granted Maternity leave, Alec Trebek did yesterday on Jeopardy, and Jeopardy is an excellent source.In her political career, Yvonne Braithwaite Burke achieved a number of firsts. In 1967, she was the first African American woman elected to the California State Assembly. In 1972, she was the first African American elected to Congress from the American West. That same year she became the first African American vice-chair of the Democratic National Committee. She was the first woman to head the Congressional Black Caucus. In 1978, she was the first African American member of the Los Angeles Board of Supervisors. Burke's most unusual first, however, is that while a member of the House of Representatives, she gave birth to a child, the first person ever to do so while serving in Congress.

I second you DG, I heard A.Trebek mention it.