On the second day of October conference 1929, LDS Church President Heber J. Grant introduced three other Presidents without warning—Sisters Louise Robison, Ruth May Fox, and May Anderson. President Grant commented,
“We have listened to a great many testimonies from our brethren during this conference.
We shall now call on some of our sisters…”
As Presidents of the General Relief Society, Young Women, and Primary Organizations each of the three women offered short witnesses. The first two clearly demonstrated their surprise at the call to speak. Read their remarks here. These three women would also speak at the two following conferences in 1930 at Grant’s request–with more warning and time for preparation. These three women were possibly the first LDS women to speak in the Salt Lake Tabernacle during General Conference, yet they were not the first women to speak in General Conference.
The current pattern of LDS female participation in General Conference is relatively recent and still not wholly static. The precedent of women speaking in General Conference was set with the first General Conference in 1845. In the morning session of the third day of that first General Conference, Lucy Mack Smith spoke in the Nauvoo Temple. It was here that Brigham Young assured the Saints of Mother Smith’s desire to join them in their journey West—the end of her address was apparently inaudible to reporters. Mother Smith and Brigham’s final comments took the whole of the morning session—an unmatched three hours.
In the first decade of the twentieth century three women spoke during conference in the overflow meetings on Temple Square. In April 1908, a 24 year old Sister Rachel Leatham and recently returned missionary Sister M.M. Lagenbucher both spoke to a few hundred waiting outside of the Tabernacle. Read it here. Likewise, the following April Sister Lilian Jones recently returned from the Southern State mission spoke to a much larger 2500 present on Temple Square. Find it here.
According to Relief Society Minutes, new Relief Society General President Belle Spafford spoke to in the priesthood session of General Conference in 1946 teaching and encouraging bishops to work in a partnership with the RS and utilize the expertise of RS presidents “In determining the needs of families receiving welfare assistance” to better meet the needs of their congregants.
Beginning in October 1976 the succeeding RS General President, Barbara B. Smith, biannually spoke in the Welfare Meeting of General Conference for the following six years through the Fall of 1982, but never in any of the regular conference sessions. (See her Oct. 1977 address here.)
In April 1984, four women spoke in conference—the new Relief Society General President Barbara Winder and the new Young Women’s General President Ardeth G. Kapp in the Sunday sessions, and the women whom they replaced–Barbara Smith and Elaine Cannon–in the Saturday afternoon session. (You can watch them here.) Four women in conference was a first, but women did not speak again in a general conference session until 1988.
In April 1988, Primary General President Dwan J. Young spoke after she was released. Her replacement, President Michaelene P. Grassli spoke the following October conference. In the 1980s and beginning the 1990s women began speaking with more regularity, but generally one woman per conference, unless an organization president was released. No women spoke at the October 1990 conference.
In general, the current scheduling of two women speaking at each biannual General Conference began in 1994. Women spoke for a time on Saturday morning and Sunday afternoon with a few shifts in the sessions. The schedule further normalized in 1998 with women usually speaking in the Saturday morning and Sunday morning session though still with a few exceptions. In 2002, the deviation from the norm was three female speakers.
Though almost twenty years is plenty of time to establish a pattern, within a church that subscribes to the possibility of change it could just as easily be time for another shift. Perhaps a prophet will yet say, “We shall now call on some [more] of our sisters.”
 Conference Report, 5 October 1929, 84.
 “Conference Minutes,” Times and Seasons, 6 no. 16, 1 Nov. 1845. My survey remains incomplete; I have been unable to review all of the conferences between this first conference and 1880. I’d love to hear any additional examples.
 Jill Derr, et al., Women of Covenant, 313.