It's common among many socially progressive couples--different sex and same sex alike--to exclaim, when one member of the partnership is pregnant, that "we're" pregnant. "When we were pregnant, Ellen got horrible morning sickness." "We're pregnant right now, so Jen's feet are swollen."
I appreciate the sentiment behind this choice of words, especially in heterosexual couples where, for logistical reasons, any attempt to equally divide the duty of pregnancy would be impossible. Namely, the couple is trying to verbally indicate that both members are invested in the creation, outcome, and, most saliently, backbreaking work associated with a pregnancy. It's nice when the man in the partnership steps out of the customary male role and contributes to the pregnancy, too, which usually means taking care of all the other miserable work (driving the future mom to doctor visits, shopping for tiny footsie pajamas, sending baby shower invites, all the usual housework) that pregnant women usually are expected to perform in addition to carrying around a 30-pound parasite with foreign genetic material for nine months. Usually the "we" designation indicates that, contrary to tradition, both mom and dad will play active roles in rearing the child-to-be. Further, exclusively referring to the pregnancy as "hers" comes off as dismissive, disinterested, or unwilling to absorb the duties that you formerly divided equally. "Oh, that's her shoe rack; I have nothing to do with that. Oh, that's her pregnancy; I'm sure glad I don't have to help out with that mess!"
On the other hand, any semantical attempt at equality aside, men simply can't get pregnant (yet!), and it's absurd and insulting to imply that the burden of pregnancy can shared equally between both partners. Sorry, bub, but you're not the one peeing on a stick, putting on weight, getting stretch marks, enduring strange hormonal shifts, passing a basketball through your vagina, getting stitched up, breast feeding, and potentially suffering severe depression as a result of this pregnancy.
This isn't to say that good future fathers don't have to do extra work when their partners are pregnant. Even soon-to-be older siblings have to pick up the slack when Mom isn't able to do all the work she normally does. But the concept of mutual pregnancy justifies related phenomena such as "sympathy weight," or the idea that PMS hurts men as much as it huts women ("She gets so irritable when she's about to start her period; it affects me, too!"). Yes, women's issues are everyone's issues, but there's no comparing being a male in solidarity to actually being a woman. (I might also accuse men who "suffer" from PMS of just being wimpy. Brother, if you had any idea how bad it actually is...)
The greater implications of a "shared" pregnancy, though no one who uses "we" has this in mind, is that ownership of the pregnancy shifts from the pregnant woman to both members of the partnership. A major tenet of abortion rights is that the pregnancy, fetus, and choice to carry the pregnancy to term belong solely to the pregnant woman, not her husband, boyfriend, father, mother, community, or local legislators. Of course the progressive men who refer to "our" pregnancy probably don't question this philosophical foundation of abortion rights. I fear, though, that many anti-feminists and anti-abortion proponents have a knack for co-opting feminist and socially progressive terminology or ideals and insidiously twisting them beyond recognition. A popular example is, "Feminists say they want to have sex as freely as men do, so it's feminists' faults when college men rape their woman classmates. These poor boys are getting mixed messages from those sex-crazed feminists!" That's not far from, "If the pregnancy is both of yours, then the fetus belongs to both of you, too. If feminists want to share the pregnancy, then men should have to approve it before their wives and girlfriends get abortions!"
Admittedly, I'm being a bit of a worry wart, and will label myself as such. In the meantime, when I get pregnant, I'll let my partner spend all the time he wants decorating for our baby shower.