The 35-year-old posed in just a bra and underwear with her bump on show in an Instagram snap posted on Wednesday.
She added a caption which read: 'We would like to share our love and happiness. We have been blessed two times over. We are incredibly grateful that our family will be growing by two, and we thank you for your well wishes. - The Carters.'
In the ethereal frame, she wore a veil on over her face while surrounded by flowers.
Her choice of a blue panties and a pink bra lead fans to speculate she's expecting a boy and a girl.
Rihanna, Rita Ora and Brie Larson were among the first celebrities to congratulate the star and her husband Jay-Z over social media.
The Single Ladies singer, who has kept out of the spotlight in recent months, and the rapper are already parents to five-year-old Blue Ivy.
In 2013, Beyonce revealed she had suffered a miscarriage prior to the arrival of her daughter.
She said at the time: 'About two years ago, I was pregnant for the first time. And I heard the heartbeat, which was the most beautiful music I ever heard in my life.
'I picked out names. I envisioned what my child would look like. I was feeling very maternal.
'I flew back to New York to get my check up - and no heartbeat. Literally the week before I went to the doctor, everything was fine, but there was no heartbeat.
'I went into the studio and wrote the saddest song I've ever written in my life. And it was actually the first song I wrote for my album.
'And it was the best form of therapy for me, because it was the saddest thing I've ever been through.'
(The track is called Heartbeat. Jay-Z also briefly referenced the miscarriage in his song Glory.)
Beyonce was thrilled when she discovered she was expecting Blue Ivy and found it hard to keep the news to herself to begin with.
Speaking in her TV show Life Is But a Dream, Beyonce said: 'Being pregnant was very much like falling in love. You are so open. You are so overjoyed.
'There's no words that can express having a baby growing inside of you, so of course you want to scream it out and tell everyone.'
Shortly after welcoming Blue Ivy, she revealed she wanted more children, telling US Vogue: 'When I was younger, there were moments where I said, "'m not going to have children, and then there were moments when I wanted four. And now I definitely want another, but I don't know when.'
She also described motherhood as 'beautiful'.
She said: 'When I wake up in the morning, the best thing in the world is seeing her face.
'It's just such a beautiful time in my life to have a child and every day see something new and see her learn something new.'
Beyonce and Jay-Z met in the late 1990s and got married in 2008.
She sent the internet into overdrive at the end of April last year with the release of her hour-long visual album in which she hinted her spouse had been cheating on her with a woman named Becky.
In one track, Sorry, Beyoncé sang: 'Looking at my watch he should have been home/ I regret the day I put that ring on/ He always got them f***ing excuses/ He only want me when I'm not on there / He better call Becky with the good hair.'
By the end of the album, the pair - who have been rocked with affair allegations for years - have seemingly patched up their differences and prepared to give their marriage another go.
However, although many fans were quick to lash out at the rapper for his alleged behaviour, some people branded it a publicity stunt to rake in cash.
The couple made no official comment on the affair rumours.
Beyoncé is pregnant with twins
Ring the alarm: Queen Bey is having twins.
The superstar singer posted a photo with her baby bump on Instagram Wednesday to announce the joyful news.
"We would like to share our love and happiness. We have been blessed two times over. We are incredibly grateful that our family will be growing by two, and we thank you for your well wishes. The Carters, " she posted.
Beyoncé and her superstar husband Jay Z are parents to five-year-old daughter, Blue Ivy.
The couple married in 2008.
The family's news set social media on fire with the Beyhive (as her diehard fans are known) buzzing about the new heir and spare. Twitter reported more than half a million tweets about Beyoncé in the first hour after her big reveal.
Beyoncé has frequently been the subject of pregnancy rumors.
In 2011, she announced the impending birth of their first child by revealing her baby bump at the end of a performance at the MTV Video Music Awards.
Fans had been tipped off earlier in the evening when she was seen cradling her baby bump on the VMAs red carpet.
Beyoncé is nominated for nine 2017 Grammy Awards and is expected to attend the ceremony on February 12. She is also scheduled to headline the Coachella music festival in April.
Beyoncé Is Pregnant With Twins
That collective shriek of joy you’re hearing from the BeyHive? Beyoncé and Jay Z are expecting twins.
The baby news was yet another example of the Beyoncé’s penchant for tightly controlling her own narrative. She revealed she was pregnant in 2011 with a knowing belly rub at the MTV Video Music Awards, after a spirited performance of “Love on Top” — and a microphone drop.
(A quick camera cut to Jay Z, born Shawn Carter, smiling ear-to-ear as Kanye West shook his rapper friend by the shoulders confirmed the message.)
Their daughter, Blue Ivy Carter, was born on Jan. 7, 2012.
While Beyoncé is famously averse to interviews and rarely discusses her personal life without setting the terms, she put the spotlight on her marriage with the release last year of the album and HBO film “Lemonade.”
It told the story of a struggling relationship, including explicit infidelity and, eventually, reconciliation. Many assumed the songs’ lyrics — which ranged from heartbroken to defiant to forgiving — were autobiographical, though the couple never revealed how much of the story was based in reality.
(In her 2013 documentary, “Life Is But a Dream,” Beyoncé discussed having an earlier miscarriage. “About two years ago, I was pregnant for the first time,” she said. “I flew back to New York to get my checkup — and no heartbeat.” Jay Z also alluded to the experience in his song “Glory.”)
“Lemonade” is nominated for a leading nine Grammy Awards at the ceremony to be held on Feb. 12. Beyoncé is also scheduled to headline the second night of the Coachella festival in the California desert on April 15 and April 22.
Things seem to be going well for the couple now — Beyoncé’s Instagram post was signed, “The Carters.”
The pair’s fervent and loyal fans responded with typical enthusiasm to the announcement: Twitter said more than half a million tweets were sent about the pregnancy within 45 minutes, and “twins” became the top trending topic.
Some Coachella ticket holders wondered about the status of Beyoncé’s scheduled performance.