Massachusetts actually already has an "egg and sperm law", enacted in 2005, that bans implanting embryos that are "not initiated by the union of an oocyte [egg] and sperm." This was part of the law that legalized SCNT stem cell research in order to lure biotech and pharmaceutical firms to Massachusetts, but this part got so little notice amidst all the talk about legalizing SCNT for stem cell research that I never realized it existed before. But is it a good enough "egg and sperm" law?
Unfortunately, like the PCBE's 2004 recommendations, it doesn't define "oocyte" or "sperm" or say if they can be engineered or derived from stem cells.
The law appears intentionally vague about requiring a man and a woman to reproduce with their natural gametes, in the very same way the PCBE's carefully chosen "two progenitors" language does. Clearly the intention is to allow people to use sperm or eggs depending on who they were hoping to conceive with, and to allow labs to create engineered gametes.
In contrast, Missouri's law limits the creation of children to the union of "sperm of a human male" and "egg of a human female", enforcing that they be actual gametes not just based on, but of an actual male and female. Of course, now there's the question of defining male and female and whether they mean legal sex or "most-likely-to-conceive-as-sex".
The legal sex of the people providing the genetic material is obviously immaterial to the lab-level ethics of trying to join their genes, but legal sex would be the first thing to check, and a lab would have to turn away people publicly of the same sex, because they are publicly prohibited. If they are not publicly prohibited, they are legally a man and a woman, but a lab might find that they were privately the same sex, and so they'd privately be prohibited from treating the couple. A legal sex-change shouldn't make it legal to do the very same unsafe genetic experiments that same-sex conception would require.
And finally, no matter what the Massachusetts law says, it is useless if another state (New Jersey, perhaps?) allows labs to attempt same-sex conception, or conception using modified or tricked gametes. Couples will just travel to New Jersey to perform the implantation and skirt around their own state's law. This is why we need a Federal law, to comply with international treaties and so that one selfish short-sighted state doesn't screw up human dignity and honor for the whole world.