Is it possible my wife is pregnant? my son is 8 months old and she's been breastfeeding him the whole time. her period first came back last month but hasn't returned. she's on day 34 of cycle now.

Yes: If you have had unprotected sex with a breastfeeding mom you can certainly start a new pregnancy.Breast feeding can decrease ovulation in some, but is not a dependable form of birth control. Have a test done and see.

Its possible: Breast feeding is fairly good contraception during first 6 months IF: 1) Breastfeeding must be the infant’s only source of nutrition. 2) The infant must breastfeed at least every four hours during the day and at least every six hours at night. 3) Mom can't have a period after 2 mo from birth. > 6 mo, or if any one of these not met, chances of pregnancy rise steeply. Get a pregnancy test.