For weeks, Hikaru Fujita, a candidate in Japan’s parliamentary elections on Sunday, wrestled with a secret. She was pregnant with her first child — a joyous milestone for her and her husband.

But Ms. Fujita, 35, a Harvard-educated former diplomat, worried that publicizing her pregnancy could hurt her campaign. In late January, she set aside her fears, announcing on social media that she had been “blessed with new life.”

“I wanted to show that even pregnant women could run,” Ms. Fujita, from Nagano Prefecture, said in an interview. “I wanted to send a message to the younger generation.”

On social media, many people celebrated Ms. Fujita’s news, while others suggested that she should pursue a career as a housewife instead, and that a maternity leave would be a waste of taxpayers’ money.

With her revelation, Ms. Fujita, who is running for a seat in the powerful House of Representatives as a candidate for the governing Liberal Democratic Party, is testing Japan’s patriarchal system. She is one of a record number of women running for parliamentary seats on Sunday; 313 out of 1,285 candidates, or almost a quarter.