It's been a while since my Constitution exam but here what is I found on a google search.

No decision of the Supreme Court in the twentieth century has been as controversial as the 1973 Roe v. Wade decision holding that women have a right to choose to have an abortion during the first two trimesters of a pregnancy. Attorneys for Roe had suggested several constitutional provisions might be violated by the Texas law prohibiting abortions except when necessary to save the life of the mother. The law was said to have been an establishment of religion in violation of the First Amendment, unconstitionally vague (the ground used in Blackmun's first draft of his opinion), a denial of equal protection of the laws, and a violation of the Ninth Amendment (which states that certain rights not specified in the first eight amendments are reserved to the people). The Court in Roe chose, however, to base its decision on the Due Process Clause of the Fourteenth Amendment and the so-called "right of privacy" protected in earlier decisions such as Griswold v Connecticut (striking down a ban on the use, sale, and distribution of contraceptives). Deciding HOW to protect the right to an abortion proved as difficult. Justice Blackmun's approach, one clerk at the time said, "As a practical matter, was not a bad decision--but as a constitutional matter it was absurd." Roe's trimester-based analysis generally prohibits regulation of abortions in the first trimester, allows regulation for protecting the health of the mother in the second trimester, and allows complete abortion bans after six months, the approximate time a fetus becomes viable.

--- http://www.law.umkc.edu/faculty/proj...w/abortion.htm