A more thorough explanation:

Planned Parenthood of Southeastern Pennsylvania v. Casey is a Supreme Court case that reaffirmed the decision of Roe v. Wade (1973) prohibiting states from disallowing abortion prior to viability. However, the Court overruled two aspects of the Roe decision: (1) the trimester distinction and (2) the use of strict scrutiny for judicial review of government regulation of abortions.

For example, the Pennsylvania Abortion Control Act of 1982 required that women seeking abortions must be given certain information at least 24 hours before the abortion was to be performed (the “24-hour waiting period”). The Supreme Court upheld the 24-hour waiting period provision and the informed consent provision for minors but struck down the spousal consent provision.

The Court characterized the issue as one of “liberty” rather than “privacy”; this opened the door for substantive due process analysis. Referring to past Supreme Court cases, the Court put an emphasis on the liberty interests and decisional autonomy of those seeking an abortion.

The Court applied stare decisis to reevaluate Roe v. Wade (1973). The Court acknowledged that the issue of abortion was highly controversial in society; however, that gave further reason for the Court to uphold precedent and avoid politicization.

Thus, the Court decided, at the time, to uphold the core holdings of Roe regarding the restrictions on pre-viability abortions. The Court had noted that while the idea of “viability” remained, the point of viability itself had shifted to earlier in the pregnancy. Pre-viability, the Court upheld the protection of the woman’s right to have an abortion, but the Court rejected the Roe’s “rigid trimester framework.”

Instead, states could not impose an “undue burden” on individuals who, prior to viability of the fetus, sought to have an abortion. An “undue burden” arose if the purpose or effect of the state restriction on abortion placed a “substantial obstacle” on individuals seeking an abortion of a non-viable fetus.

Applying the newly formed undue burden test to the facts, the Court found the spousal notification requirement to be an undue burden that impeded on a pregnant individual's decisional freedom. Thus, the Court struck down this portion of the Pennsylvania law as facially unconstitutional. However, the purpose of the 24-hour waiting period provision was to provide information to those seeking abortions. Because the state was acting in the interest of informed consent, such a provision was permissible. At the time, The Court also upheld the parental consent requirement.