Vitamin C could counteract some of the harmful effects that smoking during pregnancy can have on unborn babies, scientists say.
Vitamin C did not overcome brain development problems
High doses of the vitamin protected against nicotine-associated damage in monkeys, the Oregon Health & Science University team found.
Expert advice is still to quit smoking during, and ideally before, pregnancy.
The latest research findings appear in the American Journal of Respiratory and Critical Care Medicine.
During their experiments, Dr Eliot Spindel and colleagues found that animals exposed to nicotine before birth had reduced air flow in the lungs.
However, when the mother had taken vitamin C, the baby monkeys had lung air flow close to that of a normal animal.
The researchers are confident that their findings would be applicable to humans.
But they said giving vitamin C to pregnant women who smoke should be "a last resort".
Instead, smoking mothers-to-be should be encouraged to quit, they said.
"While we strongly encourage all women to quit smoking, this is not always possible," said co-researcher Dr Michael Gravet.
"These data suggests that vitamin C may be an important tool in preventing smoking-induced adverse outcomes."
Vitamin C did not appear to counteract any of the other negative health impacts of smoking during pregnancy on babies, such as abnormal brain development and decreased body weight.
The researchers said more work would be needed to figure out the right vitamin C dose for humans.
A spokeswoman from the National Childbirth Trust said: "The evidence on the effects of smoking on babies before and after birth overwhelmingly shows that it is detrimental to health.
"Ultimately, it is up to the mother whether she wishes to quit or not. This is useful research. Women who have not been able to give up might find it helpful to know this."