妊娠中期孕妇 lt;b gt;25- lt; b gt;羟维生素 lt;b gt;D lt; b gt;水平及其影响因素 Objective To investigate the levels of 25-hydroxyvitamin D [25 （OH） D] and its influencing factors in women during mid-pregnancy， and to provide an evidence for improving the vitamin D deficiency in pregnant women