A new congressional study says the number of people denied medical coverage because of preexisting conditions has grown by nearly half. According to the House Energy and Commerce Committee, over the last three years the four top for-profit insurers — Aetna, Humana, UnitedHealth Group and WellPoint — have denied coverage to 49 percent more people because of medical history. Over 257,000 people were denied last year, compared to 172,000 in 2007. All four companies followed a policy of considering pregnancy a “pre-existing condition” leading to an automatic denial of coverage. A provision of the healthcare law barring denial of coverage to adults based on medical history doesn’t kick in until 2014.