It's hard being pregnant.
Not only do you have to deal with morning sickness, exhaustion and insomnia — you also have to constantly be on top of the latest studies regarding what you should and should not be eating in order to develop a healthy baby.
The latest on the list of ever-changing rules is health care's stance on fish.
And while nearly all doctors agree that eating fish should be part of a healthy pregnant woman's diet, they can't seem to agree on how much to consume and which to eat.
A recent study by Harvard University scientists found that by 2050 mercury concentrations in the Pacific Ocean would be twice what they were in 1990 if the current rate of increase continues.
But scientists are still examining how ocean mercury levels affect fish mercury levels.
"There's likely a proportional relationship, but there's not enough monitoring to verify that," said Elsie Sunderland, assistant professor of aquatic science at the Harvard School of Public Health and senior author of the study.
What is clear is that if pregnant women consume fish with high levels of mercury, they may harm their fetuses.
"The concern with mercury levels in fish develops from a known problem that high levels of mercury in the bloodstream of a developing baby can lead to problems with the nervous system," said Brad Imler, president of the American Pregnancy Association.
Those health problems can include learning difficulties, cognitive deficiencies, attention deficits and impaired developmental milestones.
But it's a tricky balance. On the one hand, fish contains lean protein and Omega-3 fatty acids, which can help with fetal brain development — but you don't want to have too much mercury, which can lead to other health issues, Imler said.
The American Pregnancy Association recommends that all pregnant women stay away from swordfish, shark, king mackerel and tilefish because of their high mercury levels.
Mercury levels in other fish are less clear-cut, however.
The official recommendation is that pregnant women stick to eating two 6-ounce servings a week of fish that are believed to have lower mercury levels, such as shrimp, salmon, trout and tilapia. Even then, the rules get murky.
"The problem is, there is a huge amount of variability in fish mercury content, and while there are estimates of how much mercury each type of fish has, rising mercury in the ocean may throw those estimates off so that women who think they are staying in the OK range may be getting more mercury than they think," said gynecologist Lauren Streicher, author of "The Essential Guide to Hysterectomy" (M. Evans and Company, $17.29).
Regardless of the mercury levels, fish is still believed to be a very healthy part of a pregnant woman's diet that is hard to replace with other foods or supplements, said Ronald Krauss, certified nurse-midwife with Obstetrics, Gynecology & Menopause Physicians affiliated with Yale University in Connecticut.
"It's an ongoing, constant issue with which we have to deal," Krauss said. "You have to decide who you're going to trust, and you have to eat, you have to live, you have to be healthy. So we recommend that patients still eat fish regardless of the concerns."
Known to be off-limits
The American Pregnancy Association recommends that pregnant women stay away from swordfish, shark, king mackerel and tilefish because of their high mercury levels. But rising ocean mercury levels may implicate other fish as well.Copyright © 2015, The Baltimore Sun