Bella Hadid shares summer throwback with pregnant sister Gigi

The model gave a rare insight into Gigi's pregnancy

Bella Hadid shared a photo of her 'burger bump', with sister Gigi Hadid's baby bump. Instagram / Bella Hadid

Bella Hadid, 23, has shared a summer throwback picture of herself and pregnant sister, Gigi Hadid, 25.

In the photo, taken at sunset at the family's farm in Pennsylvania in the US, each of the model sisters, who are of Dutch-Palestinian decent, can be seen holding their stomachs. Bella captioned the shot: "Two buns in the oven except mine is from my burger and Gigi's is from Zayn."

Bella dated the photo to June 11 this year, and added: "I love you both so freaking much ... can't stop crying."

Gigi is expected to give birth this month. In August she shared photos from a July photoshoot, which she captioned, "Growin' an angel."

The model confirmed she was expecting her first child with singer Zayn Malik earlier this year. However, since the news broke, she has predominantly kept her pregnancy private.

In August, Bella opened up about her battle with Lyme disease and its debilitating effects. She was diagnosed with the illness in 2012.

Posting a list of its common symptoms on her Instagram Stories, the model used arrows to illustrate which she has suffered with.

Those she pointed to included headaches, insomnia, fatigue, anxiety, irregular heartbeat, nausea, difficulty breathing and inflammation.

"Every day I feel at least 10 of these attributes without fail ... since I was probably 14, but more aggressively when I turned 18," she said.

The model is not the only member of her family affected by the condition. Her mother, Yolanda, and brother, Anwar, also have Lyme disease.

It is transmitted to humans through the bite of infected blacklegged ticks. In addition to flu-like symptoms, it also include neurological problems and joint paint.