If such a test was used to obtain a marriage proposal are their legal ramifications to that fraud? Fraud can carry criminal sanctions if the intent was to extort money or sex from someone, and can also result in actionable civil damages. Taken one step further, if the fraud resulted in a marriage, would that marriage be legal?
While there are ways in which a marriage can be void, fraud does not automatically void a marriage. However, since marriage is a contract it can be voidable. In other words a marriage can be annulled if the contract was entered into upon the innocent party's reliance on a fraudulent misrepresentation that the offending party intended to cause the marriage.
Void vs. Voidable
A void marriage is considered to have never happened, without a court having to annul it. Examples of issues with a marriage could cause it to be void are affinity or consanguinity (incest in violation of M.G.L. c. 207 s. 1 or 2), polygamy (marrying someone when you are already married in violation of M.G.L. c. 207 s. 4), and if the spouses are under a certain age (under common law when a wife is under 12 and husband is under 14).
A voidable marriage may be annulled by a court if a party can prove that the bases for the marriage contract is improper under common law, but a voidable marriage is not automatically void. One example of an improper bases is the example of fraud described above. If a spouse tricked the other spouse into marrying them based on a misrepresentation about being pregnant, then that marriage might be voidable. Since this is a decision based in a factual analysis of the circumstances, the court would likely also consider other factors. For example, if the marriage continued well beyond the original fraud, was consummated and affirmed in other ways then it might not be voidable after a certain point. These types of cases will rely heavily on the particular circumstances.
The possibility of defeating an annulment proceeding, however, should in no-way encourage anyone to defraud someone into marrying them.
In other words, don't buy a positive pregnancy test.