In a desperate bid to have twins, CHELSEA CLINTON underwent secret fertil­ity treatments, sources tell The ENQUIRER.

After four years of marriage, the 34-year-old former first child decided to speed up the clock and com­plete her family in one fell swoop, say insiders, adding that her decision was sparked by Bill’s and Hillary’s medical problems as well as their burning desire to become grandparents.

“Instead of going through two pregnancies, Chelsea wanted to have twins,” dis­closed a close source. “She wanted to produce a family fast out of concern for her par­ents’ health – especially Bill’s.”

AS THE ENQUIRER reported last year, Chelsea and her 36-year-old investment bank­er husband Marc Mezvinsky were prompted by unexpect­ed events to consider fertility treatments.

“After years of worrying that she’d lose her dad to a heart attack, Chelsea was rocked when Hillary was hospitalized (in late 2012) with a blood clot between her brain and skull,” revealed an insider. “The clot was successfully treated and Hillary is out of the woods, but the incident made Chelsea realize that life can turn on a dime.”

Meanwhile, her 67-year-old dad had already cheated death with a lifesaving quadruple bypass surgery in 2004. He needed a follow-up operation six months later to remove fluid and scar tissue from around his heart. And in 2010, the same year Chelsea married Marc, the former president had an emergency procedure to have two stents inserted to clear a blocked coronary artery.

With the mortal­ity of her parents agonizingly evident, Chelsea and her hub­by got to work to give the aging Clintons the one thing they wanted most – grandchildren.

“They turned to fertility treat­ments because that way there would be a better chance of a mul­tiple birth,” disclosed the insider. “Chelsea’s attempt at twins didn’t work, but she is now pregnant with a single child and past the first trimester. The baby is due in the fall.”

As The ENQUIRER recently re­ported, the pregnancy has nudged Marc closer to full acceptance into the family after he infuriated Bill by taking off to Wyoming to be a ski bum early in his marriage.

In fact, a thrilled Bill gushed to his Internet followers: “Excited to add a new line to my Twitter bio…grandfather-to-be!”

An equally delighted Hillary, 66, tweeted: “My most exciting title yet: Grandmother-To-Be!”

While mom-to-be Chelsea shares her parents’ joy, the source says she’s a little disappointed not to be pregnant with twins.

“Because she was an only child who longed for a brother, she really hoped she’d have a boy and a girl,” explained the source.

But that hasn’t stopped her and Marc from begin­ning to plan a nursery in their new Manhattan apartment. “Chelsea has excitedly told pals that she’ll be spending the summer getting her baby’s nursery ready,” said the source. “And Hillary will help with the decorat­ing.”