Australia captain and Chelsea striker Kerr revealed the news on Instagram with the words "Mewis-Kerr baby coming 2025!" adding photos of herself and pregnant partner Mewis, a former United States women's national team midfielder who plays for West Ham.
Among support from well-wishers, the post also attracted some homophobic vitriol.
"It is very, very disappointing," England boss Wiegman told a news conference on Tuesday. "I'm really happy for them, they look really happy and I hope it all goes well."
Chelsea said in a statement to Reuters that they were aware of "unacceptable and hateful homophobic comments" on various social media platforms.
"There is no place in society for any form of discrimination and we will not accept any abuse directed towards our players, staff or supporters," a club spokesperson said.
"We are extremely proud to be a diverse, inclusive club that celebrates and welcomes people from all cultures, communities and identities."
West Ham shared what they called Kerr's "heartwarming" baby announcement on the team's website.
"Mewis has announced the wonderful news that she is expecting her first child," the club said.
"Everyone at West Ham United would like to congratulate Kristie and Sam on their fantastic news!"
Kerr is considered one of the world's top female strikers, scoring 199 career goals across the Women's Super League, Australia's W-League and the National Women's Soccer League, plus 69 goals for her country. But she has been sidelined since suffering an anterior cruciate ligament (ACL) injury in January.
The 31-year-old averaged nearly 30 goals in her previous three seasons for Chelsea. The 33-year-old Mewis has been capped more than 50 times for the U.S.