Not trying to imply that it doesn't. It is a stressful situation for everyone. But the rates in women are significantly higher. (Ironically being a stay at home mum can be isolating and it might be better for her health to go back to work...) One analysis also found a small be definite correlation between a mother being depressed and also the father. The incidence varies strongly depending on risk factors (smoking, obesity, poverty, trauma), form 10-25% in women, and about 5-10% in men (though men tend to under self report..).
Small study: http://bjp.rcpsych.org/content/169/1/30.short Meta study: http://jama.jamanetwork.com/article.aspx?articleid=185905