According to Sarah Pratt, he did...
In addition to Joseph Smith marrying already-pregnant women, there is some evidence that abortion was practiced in Nauvoo.
LDS Elder Ebenezer Robinson testified that Hyrum Smith "instructed me in Nov or Dec 1843 to make a selection of some young woman and he would seal her to me, and I should take her home," he recalled, "and if she should have an offspring give out word that she had a husband, an Elder, who had gone on a foreign mission." Possibly referring to a secluded birthplace, or conceivably to abortion, Robinson spoke of "a place appointed in Iowa, 12 or 18 miles from Nauvoo to send female victims to his polygamous births."
- Ebenezer Robinson to Jason W. Briggs, Jan. 28, 1880, LDS archives. On December 29, 1873, Ebenezer and Angeline Robinson signed an affidavit saying that Hyrum Smith had come to their house in the fall of 1843 to teach them the doctrine of polygamy.
The wife of Apostle Orson Pratt told Smith's son why his father had few polygamous children
"Joseph Smith, the son of the prophet, and president of the re-organized Mormon church, paid me a visit, and I had a long talk with him. I saw that he was not inclined to believe the truth about his father, so I said to him: 'You pretend to have revelations from the Lord. Why don't you ask the Lord to tell you what kind of a man your father really was?' He answered: 'If my father had so many connections with women, where is the progeny?' I said to him: 'Your father had mostly intercourse with married women, and as to single ones, (his 1st Counselor) Dr. Bennett was always on hand, when anything happened.'"
"One day they came both, Joseph and Bennett, on horseback to my house. Bennett dismounted, Joseph remained outside. Bennett wanted me to return to him a book I had borrowed from him. It was a so-called doctor-book. I had a rapidly growing little family and wanted to inform myself about certain matters in regard to babies, etc., -- this explains my borrowing that book. While giving Bennett his book, I observed that he held something in the left sleeve of his coat. Bennett smiled and said: 'Oh, a little job for Joseph; one of his women is in trouble.' Saying this. he took the thing out of his left sleeve. It was a pretty long instrument of a kind I had never seen before. It seemed to be of steel and was crooked at one end."
"I heard afterwards that the operation had been performed; that the woman was very sick, and that Joseph was very much afraid that she might die, but she recovered."
- Testimony of Apostle Orson Pratt's wife, Sarah Pratt from "Joseph Smith the Prophet: His Family and Friends"
http://olivercowdery.com/smithhome/1886WWyl.htm#pg060aA doctor in Nauvoo, and once a close associate of Jospeh Smith, was accused by Hyrum Smith of practicing abortions. Hyrum testified that former 1st Counselor Dr. Bennett was propositioning women in a similar fashion to Joseph Smith. "[Dr. Bennett] endeavored to seduce them, and accomplished his designs by saying it was right; that it was one of the mysteries of God, which was to be revealed when the people was strong enough in faith to bear such mysteries—that it was perfectly right to have illicit intercourse with females, providing no one knew it but themselves, vehemently trying them from day to day, to yield to his passions, bringing witnesses of his own clan to testify that there were such revelations and such commandments, and that they were of God; also stating that he would be responsible for their sins, if there were any, and that he would give them medicine to produce abortions, provided they should become pregnant."
- Affidavit of Hyrum Smith. Official History of the Church, Vol. 5, p.71
Pretend Marriages in Case of Pregnancy
According to church historian Andrew Jenson, Sarah Ann Whitney became the seventh plural wife of Joseph Smith, and the story of his marriage to her illustrates another strategy. She disguised her relationship to the prophet by pretending to marry Joseph Corodon Kingsbury on April 29, 1843. In his autobiography Kingsbury wrote: "I according to Pres. Joseph Smith & Council & others agreed to stand by Sarah Ann Whitney as though I was supposed to be her husband and [participated in] a pretended marriage for the purpose of . . . Bringing about the purposes of God in these last days . . ."
- Elder Joseph Kingsbury, "History of Joseph Kingsbury Written by His Own Hand," page 5, Utah State Historical Society
If Not Sex, What Was Joseph Smith Doing with His Plural Wives?
Most of Smith's plural wives boarded with other families, whom he visited periodically. His secretary, William Clayton, recorded one such visit to young Almera Johnson on May 16, 1843: "Prest. Joseph and I went to B[enjamin] F. Johnsons to sleep." Johnson himself later noted that on this visit Smith stayed with Almera "as man and wife" and "occupied the same room and bed with my sister, that the previous month he had occupied with the daughter of the late Bishop Partridge as his wife." Almera Johnson also confirmed her secret marriage to Joseph Smith: "I lived with the prophet Joseph as his wife and he visited me at the home of my brother Benjamin F."
While in hiding, Joseph Smith wrote a revealing letter which he addressed to her parents, Newel and Elizabeth Whitney, inviting them to bring their daughter to visit him "just back of Brother Hyrums farm." He advised Brother Whitney to "come a little a head and knock at the south East corner of the house at the window." He assured them, especially Sarah Ann, that "it is the will of God that you should comfort me now." He stressed the need for care "to find out when Emma comes," but "when she is not here, there is the most perfect saftey." The prophet warned them to "burn this letter as soon as you read it" and "keep all locked up in your breasts." In closing he admonished, "I think Emma won't come to night if she don't, don't fail to come tonight."
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http://www.xmission.com/%7Eresearch/family/strange.htmWhen asked in a private gathering if she was still a virgin after being the plural wife of Joseph Smith, Eliza R. Snow replied "I thought you knew Joseph Smith better than that."
- Stake President Angus M. Cannon, statement of interview with Joseph III, 23, LDS archives.
Joseph Smith Promised to Cover for Polygamy Pregnancies
Joseph Smith taught the "Law of Celestial Marriage" to his close friend and secretary, William Clayton. When the pregnancy of William Clayton's first plural wife threatened to expose them, the prophet Joseph Smith advised Clayton to "just keep her at home and brook it and if they raise trouble about it and bring you before me I will give you an awful scourging and probably cut you off from the church and then I will baptize you and set you ahead as good as ever."
- William Clayton journal, Oct. 19, 1843.
Read more here:
http://www.i4m.com/think/joseph-smith-polygamy.htm