"19 Kids and Counting" stars Josh and Anna Duggar announced Tuesday that they are expecting their fourth child.

Anna, 26, announced the news on Twitter, and it was quickly retweeted by her in-laws.

"We are so excited to announce...we're pregnant! #4andCounting #BlessingfromTheLord @joshduggar #19Kids," Anna wrote.

Thousands of people favourited the tweet, and Anna expressed thanks for the positive responses.

"Thx 4 all the well wishes!" she said. "Every life is precious & a gift from God - we're so #blessed to have baby #4 on the way! #4andCounting #19Kids."

Josh and Anna are already parents to Mackynzie, 5, Michael, 3, and Marcus, 1.

In an exclusive TLC interview, Anna revealed that she is nine weeks pregnant, and has experienced a lot of morning sickness.

"It's difficult, but it's good because I know that good things are happening," she said.

The couple also revealed that they shared the news with the Duggar family after Jessa's wedding to Ben Seewald on November 1.

"We were still visiting with the family in Arkansas, so we were really excited to get to share with the family the exciting news," Anna explained.

The pregnancy is Anna's first since the couple moved to Washington DC, and Josh discussed how their new surroundings make this pregnancy unique.

"The whole support group that we had in Arkansas, we don't have here," he explained. "We've made a lot of friends and all that, but thinking of having a baby in DC is a lot different."

"It's totally different," Anna added. "Are we going to have a home birth, are we going to have a hospital birth, or a birthing center?" she wondered. "There's so many questions that we're trying to figure out right now."

Josh's sister Jill is also pregnant. Her first child with husband Derick Dillard is due on March 24, 2015.