Merged cells from rtf to html

In the workflow of a website content management, we need to convert tables with vertically merged cells from rtf into html. The rtf files are produced by simply saving the .doc file into .rtf. No special program is used. The conversion program we use is rtf2html, v3. But it doesn’t handle merged cells conversion. The conversion program has been adapted to C++. Does someone know the codes for such a conversion? The problem is to make html identify which row the merged cell belongs to. Thanks a lot