Two teams of medical investigators — one on Long Island, another in Ohio — have opened new windows on postpartum depression, a condition that can so overwhelm some new mothers they have to be temporarily hospitalized.

Dr. Kristina Deligiannidis, a perinatal psychiatrist at the Feinstein Institute in Manhasset, found that Pitocin, a drug widely used to induce or augment labor, can have an impact on maternal mood. The drug is a synthetic version of oxytocin, the natural hormone that causes uterine contractions. Pitocin also is administered to stop postpartum hemorrhaging.

Deligiannidis hypothesized Pitocin would reduce the risk of postpartum depression and anxiety disorders, but found the opposite: Women who received it were at elevated risk of postpartum blues.

“We were really surprised by the finding,” Deligiannidis said.

The percentage of U.S. women who receive a pharmaceutical boost to induce or speed up labor ranges from 23 percent to 30 percent, federal data show.

The medication increased the likelihood of postpartum depression and anxiety regardless of the women’s history of depressive illness, Deligiannidis found.

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For those with a pre-pregnancy history of depression or anxiety, Pitocin increased the risk of postpartum blues by 36 percent compared with women who did not have the drug injected. Having no history of the disorders, the risk was 32 percent, Deligiannidis said.

Postpartum depression is a well known consequence of giving birth, doctors say, affecting 12.9 percent of women. Postpartum anxiety disorder affects about one-fifth of new mothers. Locally, the women’s unit at Zucker Hillside Hospital in Queens, a psychiatric facility, has a special program for postpartum depression.

The research by Deligiannidis, however, is statistical, which found correlations between Pitocin and postpartum blues. While it can be argued that correlation isn’t causation, Deligiannides said it would be unethical to give the drug to women in labor just to test a hypothesis.

Other doctors have suggested consequences for the baby when their mothers received Pitocin. In 2013, a Manhattan researcher reported higher rates of neonatal intensive care admissions and lower Apgar scores. An Apgar test, based on a scale of 1 to 10, is performed on a newborn at one minute and five minutes after birth to reveal how well an infant is thriving. Most babies score between 7 and 9.

Dr. Michael Tsimis of Beth Israel Hospital found that infants whose mothers received Pitocin were more likely to have worrisome Apgars of less than 7.

Mothers, meanwhile, have a tough time fighting postpartum blues, said Deligiannidis who studied the cases of more than 40,000 women. “There are many women who just before they breast feed become very sad, and they sob,” she said.

Theory has long held that dramatic hormone changes immediately after birth — typified by a plunge in maternal hormones — can affect mothers’ moods. Aside from that, the exact cause of postpartum blues remains a mystery.

“Nobody knows what the exact mechanism is, what triggers the depression. But it is felt that some women may have had underlying depression,” said Dr. Scott Berlin, an Islip obstetrician and gynecologist, not connected with the research.

Yet as with all things in science, there is no single answer. As Deligiannidis reported her results on Long Island, researchers in Ohio found another possible clue.

Lisa Christian of Ohio State University investigated the brain and linked the decrease in a hormone called brain-derived neurotophic factor, or BDNF, to postpartum blues.

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“Women who had steeper declines of BDNF had a greater risk for depression late in pregnancy and also had a higher risk for delivering babies of low birth weight,” Christian said.