Criminal Consequences Of Adultery
State Criminal Laws
In a large majority of U.S. jurisdictions, adultery is no longer a crime (assuming the sexual act is consensual and not incestuous) including 35 U.S. states, the District of Columbia, and the several U.S. territories. "States which have decriminalised adultery in recent years include West Virginia (2010), Colorado (2013), New Hampshire (2014), Massachusetts (2018), Utah (2019), Idaho (2022), and Minnesota (2023)."
Adultery is rarely enforced criminally in the 15 states and Puerto Rico, as of 2023, that still do have adultery laws on the books that have not been held unconstitutional by state courts. This is, in part, due to doubts about the constitutionality of these crimes under federal and state constitutions, in part, due to changing norms, and in part, due to the limited benefit of a misdemeanor or felony prosecution to all persons involved (and the state) in such cases.
The birth of a child who is conceived with a father other than the mother's husband while the mother is married is not automatically conclusive proof of the crime of adultery under either state law or under the U.S. Code of Military Justice.
For example, under South Carolina law adultery involves either "the living together and carnal intercourse with each other" or, if those involved do not live together "habitual carnal intercourse with each other" which is more difficult to prove. Similarly, in Florida, the crime is "Living in open adultery".
Also, in the case of a prosecution of an unmarried man, knowledge that the woman is married would typically be an element of the crime of adultery, and it is similarly never a crime to be raped in the U.S., even if you are married.
In 12 of the states where adultery is still a crime (Arizona, Alabama, Florida, Georgia, Illinois, Kansas, Maryland, Mississippi, New York, North Dakota, South Carolina, and Virginia), it is a petty offense (the maximum punishment in Maryland is a $10 fine), or is a misdemeanor. But it continues to be a felony in 3 states (Oklahoma, Michigan, and Wisconsin) and is punishable most severely among those states in Michigan who someone convicted of adultery faces up to four years in prison and in Oklahoma where the maximum sentence is five years in prison.
It is a crime that is actively enforced for active duty members of the U.S. military under the U.S. Code of Military Justice.
In the U.S. military, adultery is a potential court-martial offense, falling under the General article (Art. 134). The Manual for Courts-Martial defines (para. 99) "Extramarital sexual conduct" as being:
Elements.(1) That the accused wrongfully engaged in extramarital
conduct as described in subparagraph c.(2) with a certain person; (2)
That, at the time, the accused knew that the accused or the other
person was married to someone else; and (3) That, under the
circumstances, the conduct of the accused was either: (i) to the
prejudice of good order and discipline in the armed forces; (ii) was
of a nature to bring discredit upon the armed forces; or (iii) to the
prejudice of good order and discipline in the armed forces and of a
nature to bring discredit upon the armed forces.
U.S. military law on adultery was revised in 2019 in order to include same-sex encounters in the offense.
Neither the U.S. military, nor any U.S. state, has penalties for adultery that differ depending upon whether or not the adultery results in the birth of child.
The U.S. Supreme Court has not ruled on the constitutionality of adultery crimes since its ruling in Lawrence v. Texas, 539 U.S. 558 (2003) which decriminalized any kind of sex between consenting unmarried adults that does not constitute prostitution, as a matter of constitutional law (including sex between married adults with each other).
The highest court of the State of Massachusetts declared its adultery statute unconstitutional as a violation of the U.S. Constitution in the case of Commonwealth v. Stowell, 449 N.E.2d 357, 389 Mass. 171 (1983). But, the U.S. Supreme Court's decision in Bowers v. Hardwick, 478 U.S. 186, 106 S.Ct. 2841, 92 L.Ed.2d 140 (1986), holding that the U.S. Constitution did not invalidate a state sodomy statute in a case involving tow consenting men, largely discouraged constitutional challenges until Lawrence overruled Bowers v. Hardwick in 2003. See, e.g., Oliverson v. W. Valley City, 875 F. Supp. 1465, 1482 (D. Utah 1995) (holding that "The claim of the right to commit adultery cannot be considered “fundamental.", and denying a constitutional challenge to a police officer being disciplined for adultery while not on duty, in reliance on Bowers v. Hardwick).
In the two decades prior to Lawrence, however, no state or federal court has declared an adultery statute unconstitutional on U.S. Constitutional grounds, despite the fact that there have been a handful of adultery prosecutions in this time period in some of the states where adultery remains a crime.
For example, there was one prosecution in Virginia in 2004, and another one in New York State in 2010. On the other hand, the last time someone was prosecuted for adultery in Wisconsin was in 1990. I am not aware of any post-Lawrence adultery prosecution by a state government that has led to appeal that produced a published or binding precedents on the issue of the constitutionality of these state adultery statutes. This is, in part, because prosecutions for adultery in state courts are rare and are misdemeanor prosecutions in most cases. But, appeals of minor misdemeanor convictions are rare.
Courts within the U.S. military justice system, at least, have expressly rejected constitutional challenges to the Uniform Code of Military Justice's adultery prohibition since Lawrence was decided. See, e.g., C. Scott Maravilla, "Prosecuting Adultery Under the Uniform Code of Military Justice After Lawrence V. Texas" (July 29, 2007).
Other Criminal Law Considerations
Giving birth itself, regardless of the circumstances, is never a crime in the United States.
Some sexual acts which can sometimes result in the conception of a child are crimes (most obviously incest and rape, including statutory rape and abuse of a position of trust rape). But these offenses are not related to marital status unlike a true adultery charge.
A murder of the spouse or the non-spouse with whom that spouse is engaged in adultery in the heat of passion immediately following the discovery of them "in the act" is a mitigating factor. This can reduce a murder charge to a manslaughter charge in many states. This incomplete defense to a murder charge is known as the "heat of passion" defense.
The U.S. Supreme Court has also held that the "other man" in an affair with a married woman who gives birth as a result does not have a constitutional right to seek to have his paternity of the child legally established. See Michael H. v. Gerald D., 491 U.S. 110 (1989).
Thus, the standing of the "other man" to bring suit to determine that he is the father of such a child is purely a matter of state law.
The state laws addressing this question and some related questions are addressed in the article, "TRUTH AND CONSEQUENCES: PART II: Questioning the Paternity of Marital Children" (2002) by Paula Roberts.
In a handful of U.S. states a husband can bring a lawsuit for money damages (called alienation of affections or "criminal conversation" despite the fact that it is a civil lawsuit) against someone who has sex with his wife. The vast majority of U.S. states have abolished such lawsuits, however.
In fiscal years 2000–2007, there were an average of 230 alienation of affections filings in North Carolina per year — a bit over 0.5% of the number of all divorces. The tort is also recognized in Hawaii, Illinois, Mississippi, New Mexico, South Dakota, and Utah, but it is frequently litigated only in North Carolina and in Mississippi.
Many of the states where the tort is not commonly used impose restrictions on it that make it less attractive. In Illinois, Hawaii and New Mexico, these limitations make it exceedingly difficult to prevail in an alienation of affections case and recover substantial monetary damages. The standard of proof is lower in Utah and South Dakota, which continue to have actively litigated alienation of affections suits, although not used as often in these states as in North Carolina and Mississippi, for reasons that are presumably unrelated to the relevant legal standards that apply to these lawsuits.
Also, in a rape case, a rape victim can bring a civil lawsuit for money damages against the rapist for assault and battery in most cases, and in those cases, many states allow a spouse of a rape victim to bring a parallel lawsuit against the person who committed the assault that is called a lawsuit for loss of consortium. The right to sue for loss of consortium is not specific to rape cases; it applies in all lawsuits for personal injury where it is available.
Civil lawsuits involving rape cannot be subject to arbitration requirements by a pre-dispute contract between the parties to submit all disputes between them to arbitration (e.g. in a suit between an employee and an employer related to conduct that facilitated a co-worker's rape of the employee under sex discrimination laws) under a federal law enacted effective in the year 2022.
The U.S. Supreme Court has repeatedly declined to grant petitions for certiorari seeking to have laws establishing civil liability in these cases declared unconstitutional.
In most U.S. state, divorce is granted without regard to marital fault and adultery is not considered in alimony awards or property divisions.
While every U.S. state has some form of no fault divorce, and number of U.S. states also have fault based divorce, and a number of U.S. states, however, allow consideration of adultery as a form of marital fault in divorce proceedings, including how much, if any alimony is awarded and in property divisions.
No state would consider being raped an act of marital fault, however, even if this caused a wife to give birth to a child whose biological father was not her husband, and even if the husband wanted her to have an abortion.
Selected Non-U.S. Criminal Adultery Laws
Adultery is no longer a crime in any European country, Turkey, Australia, South Korea, Japan, Taiwan, the People's Republic of China, or India. Adultery is no longer a crime in most or all of Latin America.
Adultery is a crime in the Philippines (in a manner that punishes married women more severely than married men). It is notable that in this case, that the Philippines has a significant Muslim minority population. Adultery is also a crime in Indonesia and in Bangladesh.
Adultery is also a crime according to Wikipedia at the first link in this answer, in "several sub-Saharan African Christian-majority countries." One of these countries is Rwanda.
And, according to Wikipedia at the first link in this answer:
In Muslim countries that follow Sharia law for criminal justice, the
punishment for adultery may be stoning. There are fifteen countries in
which stoning is authorized as lawful punishment, though in recent
times it has been legally carried out only in Iran and Somalia.
Countries which follow very strict versions of Sharia law in their
criminal systems include Saudi Arabia, Iran, Brunei, Afghanistan,
Sudan, Pakistan, 12 of Nigeria's 36 states (in Northern Nigeria) and
Qatar; although these laws are not necessarily enforced. Al-Shabaab, a
jihadist fundamentalist group based in East Africa (mainly Somalia)
and Yemen also implements an extreme form of Sharia.
Obviously, this answer is not absolutely complete. It leaves the status of a number of particular countries unresolved.