In the very late 1800's, Victorian ladies began having teas for mommy but not until after the baby was born because pregnant women did not appear in public. In the early 1900's, the teas transformed into "showers" (based on the "showering" of the bride before her marriage) and umbrellas became symbolic because it was customary for ladies to carry parasols when they attended these afternoon gatherings. The gifts given to the new mom were very practical in nature as well as handmade.
A baby shower was originally offered for the first baby of the mommy-to-be but that tradition has changed to being for all "new additions" to a family since they are all miracles and deserve to be showered with love and gifts.