Study Says Fish Can Make Unborn Children Smarter

A new medical report is surprising and confusing mothers-to-be.

For years, pregnant women have been told to avoid eating certain types of fish because they may contain high levels of harmful mercury. But this new study claims eating fish can help boost the IQ of unborn babies.

The study, led by Dr. Joseph Hibbeln of the U.S. National Institutes of Health, found that women who had eaten no fish were more likely to have babies with poor communication skills at 18 months, poor fine motor coordination at age 3½, and poor social behavior at age 7.

ABC News medical contributor and Yale University professor Dr. David Katz visited "Good Morning America Weekend" to clear up the confusion.

"The punch line is that the findings in this study are actually pretty consistent with the advice we had all along," Katz said. "Eating some fish is clearly better than eating no fish at all. There was never a recommendation to eat no fish."

Limit Intake of Certain Seafood, But Don't Avoid It Altogether

Katz said that for pregnant women, the real concern is mercury, which is concentrated in a few types of fish -- swordfish, tuna mackerel and shark. Pregnant women should limit their intake of these types of fish, but shouldn't avoid fish altogether.

"Don't throw out the baby with the bath water, Katz cautioned. "If you eat no fish at all, there may be a disadvantage. The reason is omega 3 fatty acids, which are found almost uniquely in fish and seafood, and are very important to brain development."

The science behind Hibbeln's study isn't very strong, according to Katz.

"These scientists measured diet and did surveys to measure intelligence, but they didn't control anything so other factors varied," he explained. "Women who ate more fish also were more likely to breast feed. They were less likely to smoke. Any of these other factors could partly explain the differences seen in intelligence, and those differences were relatively small."

Katz advised that pregnant women eat up to three servings of seafood per week, but not eat swordfish or shark and limit intake of tuna. Women who don't like fish can get omega 3 fatty acids from a supplement, as long as it's free of mercury.

"If you check out the supplement to make sure it's free of mercury, you get all the benefit and avoid the harm completely," he said. "I've been through a lot of pregnancies in my home, and I always recommended omega 3 supplements to my wife. I would recommend that to anybody."