overall coupled with increased demand for more modern alternatives such as resin composite fillings (which match the tooth color), as well as public concern about the mercury content of dental amalgam, have resulted in a steady decline in dental amalgam use in developed countries, though overall amalgam use continues to rise worldwide. Given its superior strength, durability, and long life relative to the more expensive composite fillings, it will likely be used for many years to come. Over a lifetime, dietary sources of mercury are far higher than would ever be received from the presence of amalgam fillings in the mouth. For example, due to pollution of the world's oceans with heavy metals, products such as cod liver oil may contain significant levels of mercury. Prenatal There is little evidence to suggest that amalgam fillings have any negative direct effects on pregnancy outcomes or on an infant post-pregnancy. A study, consisting of 72 pregnant women, was conducted to determine the effects of dental amalgam on babies in utero. Results indicated that although the amount of amalgam the mother had was directly related to the amount of mercury in the amniotic fluid, no negative effects on the fetus were found. A larger study, consisting of 5,585 women who had recently given birth, was used to determine if amalgam restorations during pregnancy had any effects on infant birthweight. Among the study group, 1,117 women had infants with low birth weights and 4,468 women had infants with normal birth weights. Approximately five percent of the women had one or more amalgam filling restorations during their pregnancy term. These women had little to no difference in infant birth weight compared to the women whom did not undergo amalgam restoration during pregnancy. Public awareness A 2006 Zogby International poll of 2,590 US adults found that 72% of respondents were not aware that mercury was a main component of dental amalgam and 92% of respondents would prefer to be told about mercury in dental amalgam before receiving it as a filling. A 1993 study published in FDA Consumer found that 50% of Americans believed fillings containing mercury caused health problems. Some dentists (including a member of the FDA's Dental Products Panel) suggest that there is an obligation to inform patients that amalgam contains mercury. A prominent debate occurred in the late 20th century, with consumer and regulatory pressure to eliminate amalgam being "at an all-time high".