WASHINGTON — For years, the weather has been blamed when there are alleged cabin-fever-induced spikes in births. Now, some in the Washington, D.C., area are pointing to Congress to explain packed maternity wards at several local hospitals.

In July, nine months after Congress failed to pass appropriations legislation — shutting down much of the government and sending thousands of federal workers home for more than two weeks — some hospitals are reporting higher-than-average numbers of births. Skeptics say the coincidence is probably another false “baby boom” claim, the same as those made after hurricanes, snowstorms and even the Sept. 11 attacks.

“Usually these stories are just romantic hypotheses with nothing to support them,” said Philip Morgan, a professor at the University of North Carolina, Chapel Hill, who directs the Carolina Population Center. “A few hospitals will have extra babies, so if you go looking for evidence, you can find it.”

In 1970, statistician Richard Udry published an analysis of a supposed baby boom reported by The New York Times nine months after a blackout had hit the city in fall 1965. Examining the statistics compared with averages from several years before, Udry found no evidence of a real rise in births.

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Still, even Udry knew his evidence would hardly quell excitement related to reports of such booms. “It is evidently pleasing to many people to fantasy that when people are trapped by some immobile event which deprives them of their usual activities, most will turn to copulation,” Udry wrote.

UNC’s Morgan said such events were unlikely to affect the birthrate because they rarely had an effect on other factors, such as couples using contraception. However, he said some cases had been scientifically corroborated, including a rise in births in metropolitan Oklahoma City after the bombings in 1995 and a decrease after the 1954 Brown v. Board of Education Supreme Court decision in Southern states.

“It’s possible, but I doubt it,” Morgan said. “If anything, the government shutdown would irritate people and make them rethink having a child.”

The spike in births in at least one hospital has people excited. “It’s not actually a rumor; it’s real,” said Gary Stephenson, a spokesman for Sibley Memorial Hospital in Washington, who said the hospital had averaged three more births per day in July compared with last year.