The birth rate began returning to normal in several leading hospitals here yesterday following a sharp rise nine months after the 1965 blackout.
Fertility experts and statisticians, meanwhile, disclosed studies that linked increased birth rates to times of crisis.
Figures released by St. Luke's Hospital, which reported three times the average number of births daily for a seven-day period, dropped to nearly twice the average Wednesday, the last day for which figures were available. The hospital, which averages 5 births daily, had 14 to 15 births for a week, and 9 births Wednesday.
Mount Sinai Hospital, which had 28 births Monday, had 16 Tuesday and 17 Wednesday, compared with an average of 11, for the largest three-day total in the hospital's history.
Bronx Municipal, which averages 7 births daily, had 16 Tuesday, but only 9 Wednesday; Brookdale, which averages 10, had 15 on Monday and Tuesday, and 14 on Wednesday. Brooklyn Jewish, which averages 15, had 18 on Wednesday.
An average number of births on Wednesday was reported by New York Hospital, Columbia-Presbyterian, St. Vincent's, Cumberland, Methodist, Harlem, Coney Island, French, University Jewish Memorial and Kings County hospitals. Far below average was Bellevue, where only one birth was reported, compared to an average of six.
A relationship between birth rates and crises was disclosed yesterday by statisticians of the National Office of Vital Statistics. Its figures showed that seasonally adjusted fertility rates rose sharply nine months after national and international crises. The statistics are based on the number of births per 1,000 women 15 to 44 years of age, adjusted for seasonal variations. August and September are the heaviest months. The rate so far this year is 93.
For example, nine months after Pearl Harbor Day, the national birth rate, which usually fluctuates by a point or two, rose eleven points. In New York City the rise was so swift that the Health Department ran out of birth certificates.
The national birth rate also rose nine months after the outbreak of the Korean war. The rate dropped by six points nine months after the assassination of President Kennedy.
The highest recorded national birth rate occurred in August of 1956, with 134 births per 1,000 women. No major national event was recorded nine months previously. Ten and a half months earlier, however, President Eisenhower had a heart attack.
Dr. Christopher Tietze, research director of the National Committee on Maternal Health, recalled a month-by-month study of births in the Netherlands that disclosed a sharp rise.
However, he said that he was "deeply skeptical" of any relationship between the blackout and the purported birth rise. "I'll wait until we get all the births in the city," he said.
Dr. Alan F. Guttmacher, president of the Planned Parenthood Federation of America, pointed out that August is normally a heavy month for births, and called the relationship between the blackout and the birth increases "a most engaging happenstance."