Hola YCAIRES,
Prueba esto:
<div class="row">
<div class="input-group">
<span class="input-group-addon"><span class="glyphicon glyphicon-user"></span>
</span>
<select name="Sexo" id="Sexo" class="form-contol">
<option value="">Seleccione…</option>
<option value="1">Masculino</option>
<option value="2">Femenino</option>
</select>
</div>
</div>