Would appreciate if posters included diagrams or illustrations that show what massages a husband can perform on his wife who is pregnant (going to give birth in 3 to 4 months time) and help her to reduce stress?
My wife's favorite pain relief technique for me to do was taught us by our childbirth instructor. The baby puts a lot of outward pressure on the pelvis, so to provide relief you squeeze her hips together in the back. It sounds really weird, but judging from her reaction it feels amazing. I think it works because your muscles temporarily take the strain instead of hers.
I don't have diagrams or illustrations for you, but I'd suggest you look up pressure points and basic massage techniques and then just listen to your wife. By "listen" I mean listen to what she says about how your massage feels and watch for signs of relaxation. If she sighs or starts seeming more relaxed, you are doing great! If she gets more tense you might try backing off on pressure or asking her where to try next.
Lamaze classes can actually help with the basics in massage technique for pregnancy, but since every woman is different and carries both the baby and her stress in her own unique way, no matter what info you get, you will need to be very attentive to her reactions about it. When I was pregnant, I was sick all the time and went through points when I didn't want anyone to touch me at all (it often brought on waves of nausea).
I suggest you experiment and pay close attention. Ask her what feels great and listen to her when it doesn't.
My boyfriend does the hip squeeze thing and it is awesome. Regular back and foot massages help, too, and I've had a lot of back pain. The one thing our midwife pointed out, though, is do not massage or squeeze the Achilles's tendon or the area between the thumb and forefinger. Massaging these areas can lead to contractions.