Artificial insemination is not the same as in vitro fertilization (IVF).
Artificial insemination involves introducing donor semen (from the spouse or another male) into the woman's body.
IVF involves extracting eggs, and adding sperm to fertilize them outside the mother's body - the so-called test-tube baby. This is generally the method of choice for infertile couples. It can be accomplished using sperm from the husband and eggs from the wife, and/or donor sperm and eggs.
The last directive that I am aware of from the WTS is in the March 1993 WT on the topic of surrogate motherhood. They take the position that the woman's body belongs to her husband (or possible future husband) and if her body is impregnated by someone other than her husband, it is considered to be an act of fornication or adultery.
That was actually one of the articles that got me thinking about how stupid the WTS rules are. It occurred to me that Jesus never would have been born if Jehovah didn't use Mary's body (which technically "belonged" to Joseph by way of betrothal) - did that make Jehovah an adulterer? It's quite funny the reaction of JWs - when I brought up the contradiction, all of them claimed that Jehovah didn't have to follow his own rules and could basically do whatever he wanted.
As far as the process involving masturbation to procure a "donation", the issue was not addressed in the article, however the WTS has had a don't-ask-don't-tell policy for what goes on between married couples for quite some time. It's plausible that a couple could claim that ejaculation was the result of intimacy / foreplay between them, rather than masturbation.