Sienna Miller Wore Boyfriend Oli Green's Jeans for the First 4 Months of Pregnancy: 'I Have Outgrown Them'

"I've tried to avoid buying maternity wear. It's very hard,” Miller noted

Sienna Miller has turned to boyfriend Oli Green for maternity wear.

The North Star star, 41, revealed in a new interview with Vogue that she’s been getting creative with her pregnancy outfits, turning to Green's closet.

"I've tried to avoid buying maternity wear. It's very hard,” Miller said. “I feel like I'm probably at the stage where I need some maternity leggings.”

“I've found clothes in my wardrobe that will stretch and I have borrowed Oli's jeans for the first four months,” she added. “I have now outgrown them.”

Related: Pregnant Sienna Miller Bares Her Bump on Vogue Cover — and Accidentally Reveals the Sex of Her Baby on the Way

Though the actress noted that there have been some plus sides to her current pregnancy, including “the timing.”

“I think that the timing of this pregnancy is great,” she said. “I got to be sort of floaty in the summer. And, you know, in the good stage of pregnancy, [I] was in easy clothes, and now I can just like jumper it up."

Despite having a hard time finding maternity clothes, the Anatomy of a Scandal star has pulled off several high-fashion moments with her bump on display. Miller, who features on the cover of Vogue’s December issue, posed in several looks including a navy blue knit sweater that cuts off just before her stomach and black bikini bottoms.

She also posed in a black striped jacket and pant combination, with the jacket unbuttoned to show off her growing baby bump, and posed by the beach in a flowing red v-neck satin gown, which accentuated her curves.

Related: Pregnant Sienna Miller Wears Epic Cut-Out Two-Piece at London Fashion Week

During the Vogue World Show during London Fashion Week in September, she also created an unforgettable style moment with her baby bump.

The Extrapolations star wore an epic cropped white, long-sleeve Schiaparelli top that stopped just before her bump, baring her belly, and matched it with a voluminous Schiaparelli white skirt. She posed on the red carpet at the event — which kicked off London Fashion Week — with her hand on her hip.

Miller revealed during the Vogue interview that she and Green, 27, are expecting a girl, who will join Miller’s other daughter Marlowe, 11, whom she shares with actor Tom Sturridge.

Asked if Marlowe is excited to be an older sibling, Miller says, "To have a sister? A baby sister? Oh, gender reveal by accident. I'm having a baby girl."

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In November, Miller’s sister shared photos from the actress’ baby shower on Instagram, writing, “Last night we showered @siennathing in love in preparation for the most exciting arrival. It was pure magic.” She added, “I can’t wait to meet the newest member of our family 💕🌸🩷🌸💕🌸🩷🌸💕.”

The shower featured a gorgeous array of pink decor, including some impressive balloon displays, a flower crown for Miller, and several pink-centric bouquets. There was also a nail art station for guests.

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