In 2002 Sylvia Ann Hewlett terrified career-oriented women when she hit them with a cold truth: Regardless of advances in medicine, it’s difficult for women to get pregnant beyond their early 30s. If women wanted to have children, her book Creating a Life urged, they better leave their desks and start planning. Now.

The book sparked a media flurry and spawned a decade’s worth of articles spouting largely the same statistics chronicling women’s waning fertility. “Fifty percent of women over 35 will fail to get pregnant over the course of eight months,” warned New York Magazine in 2010, “and after that the odds keep dropping.” In June, the Wall Street Journal warned readers that fertility rates “gradually begin to decline around age 32 and then rapidly decline after age 37.” The articles have become so frequent they have birthed a new genre: lady panic.

But in this month’s Atlantic cover story, Jean Twenge goes on a factchecking deep-dive through the most commonly bandied about statistics and comes to a pretty shocking conclusion: Everything you’ve ever heard about the biological clock has been wildly distorted. Take this report, for example:

The widely cited statistic that one in three women ages 35 to 39 will not be pregnant after a year of trying, for instance, is based on an article published in 2004 in the journal Human Reproduction. Rarely mentioned is the source of the data: French birth records from 1670 to 1830. The chance of remaining childless—30 percent—was also calculated based on historical populations.

“In other words,” Twenge writes, “millions of women are being told when to get pregnant based on statistics from a time before electricity, antibiotics, or fertility treatment.”

And, in other words, no journalist bothered to read (or report on) the methodology of the study.

Failing to mention the century of your statistics is pretty bad, but it gets worse. Twenge traced a number of the most incendiary facts, including the oft-spouted statistic that “20 percent of 30-year-old women and 5 percent of 40-year-old women get pregnant per cycle,” to pamphlets released from the American Society for Reproductive Medicine, which she called asking for citations. Apparently she’s the only journalist in a decade to probe the information: not only could they not provide corroborating studies, they admitted to massaging the statistics for simplicity.

Now, the onus for the botched facts doesn’t fall entirely on lazy reporting. Part of the reason that journalists are spouting historical figures is that scientists, too, have been relying on ancient data sets. Pregnancy, it turns out, is a difficult thing to evaluate. There’s only a short period to find couples trying to get pregnant before some of them become pregnant and drop out, throwing off the data pool. And by the time prospective parents reach their late-30s the pool is already corrupted by the super-fertile twenty-somethings who get knocked up early and don’t, but probably could, continue procreating into their late-30s and 40s. (Twenge recommends looking at studies of cycle viability, which monitors couples day-by-day as they attempt get pregnant.)

But as she deftly reports, had journalists bothered to review the research holistically, even the small body of contemporary research paints a more optimistic picture of the biological clock:

In one study… David Dunson (now of Duke University), examined the chances of pregnancy among 770 European women. It found that with sex at least twice a week, 82 percent of 35-to-39-year-old women conceive within a year, compared with 86 percent of 27-to-34-year-olds. (The fertility of women in their late 20s and early 30s was almost identical—news in and of itself.)

In CJR’s January cover story, “Survival of the Wrongest,” writer (and Atlantic contributor) David H. Freedman recounts the chronic inconsistency of reporting of health findings. Freedman blames this on the breadth and variation of scientific inquiry—where many incremental findings amount over time and frequency to a solid fact—allowing journalists hand-select the evidence that fits their final argument.

The problem isn’t just a lack of context; some of the arguments are heightened by partially omitting facts. Take Down syndrome, cited often by the press as a risk of having children late. It’s true that babies conceived by older women are at higher risk of Down syndrome. But it’s not a particularly high risk: Of children birthed by women in their 30s, 99 percent don’t have the mutation. The argument that younger women respond better to in-vitro fertilization, is also factually accurate. But rarely do stories include the fact that just one percent of American children are conceived through IVF. (This makes it particularly strange when Twenge concludes her piece by encouraging young women to freeze their eggs, so they may take part in IVF later on.)

Alexis Sobel Fitts is a senior writer at CJR. Follow her on Twitter at @fittsofalexis.