The above is a well informed and cogent summary of the matter with one exception.
Roe v. Wade is predicated on the
Griswold v. Connecticut line of
decidendi regarding a supposed constitutional right of privacy.
In legal terms penumbra is most often used as a metaphor describing a doctrine that refers to implied powers of the federal government. The doctrine is best known from the Supreme Court decision of GRISWOLD V. CONNECTICUT, 381 U.S. 479, 85 S. Ct. 1678, 14 L. Ed. 2d 510 (1965), where Justice WILLIAM O. DOUGLAS used it to describe the concept of an individual's constitutional right of privacy.
Writing for the majority in Griswold v. Connecticut, Douglas "used the term [more at cited the doctrine] when he wanted to refer to a peripheral area or an indistinct boundary of something specific."
In his opinion, Douglas "stated that the specific guarantees of the
BILL OF RIGHTS have penumbras "formed by emanations from those guarantees that help give them life and substance," and that the right to privacy exists within this area [i.e., the area of contraception].
Since Griswold, the penumbra doctrine has primarily been used to represent implied powers that emanate from a specific rule, thus extending the meaning of the rule into its periphery or penumbra.
Griswold v. Connecticut declared that this right of general privacy is implicitly inherent to the collective penumbra of the First, Third, Fourth, Fifth, and Ninth Amendments.
Hence, the right of privacy was formally established in
Griswold v. Connecticut, and in
Roe v. Wade, the Court extended this penumbra of privacy to entail relatively unfettered access to abortion during the first two trimesters.