Critics argue that it has toxic effects that make it unsafe, both for the patient and perhaps even more so for the dental professional manipulating it during a restoration. A study by the Life Sciences Research Office found that studies on mercury vapor and dental amalgam "provided insufficient information to enable definitive conclusions." They identified several "research gaps", including: "well-controlled studies using standardized measures that evaluate whether low level vapor exposures produce neurotoxic and/or neuropsychological effect", studies on "co-exposure to HgO and methylmercury", studies on "in utero exposure to HgO", "occupational studies on workers with well-defined HgO exposure", studies on the absorption of Hg2+ by the "human neonatal gut from breast milk", studies on "whether dental professionals have increased incidences of kidney disease, emotional instability, erethrism, pulmonary dysfunction, or other characteristics of occupational HgO exposure", studies on whether there exist "potential gender differences" or "genetic basis for sensitivity to mercury exposure." The removal of amalgam fillings is not recommended for reasons other than a true hypersensitivity to mercury. Mercury levels in blood and urine have been shown to rise for a short period of time following the removal of amalgam restorations and no studies have demonstrated any health gain from restoration removal. Removal involves exposure to mercury vapor released during the removal process. Amalgams also contribute to mercury toxicity in the environment. With regard to amalgam placement and removal in pregnancy, research has not shown any adverse effects for the mother or fetus. However, research is inadequate to determine the chance of harm occurring and therefore placement and removal should be avoided during pregnancy if possible.