Having already instructed his readers on How To Be a Jewish Mother and How To A void Love and Marriage, humorist Greenburg now demonstrates how to write an achingly sincere, numbingly unfunny book about post-""Lib"" paternity. Greenburg, by his own account, decided in early 1984 to sire, at 48, an offspring for the first time. He began a diary in which he would trace the conception, gestation, delivery and infancy of his child--a son, Zack, as it happened, born March 8, 1985, at New York Hospital. The literary result of this laudable, if not entirely original, project is now available to anyone with a high tolerance for clinical detail (episiotomies, Ovulindex thermometers, ""diarrhetic diapers""), conjugal cuteness (""Is there time for me to take a poop?"") and shameless name-dropping (""Our friend, Linda Lavin,"" ""A guest named Clay Felker""). Greenburg's entries deal with such matters as morning sickness, the ""horrors"" of childbirth, breast feeding, the urinary habits of male infants, the problems of post-parturient coitus. The anecdotes are so breathlessly recounted that it seems the author is unaware they've been around since Adam and Eve first tried to get Baby Cain to taste applesauce. There is, to be sure, something vaguely endearing about Greenburg's obvious delight in his new-found role, but, for anyone who's ever been trapped in the company of a first-time father, it's all too familiar. The only thing missing? Snapshots. Greenburg would perhaps have been better advised to put off writing his book until he was able to distance himself a bit from his material. Humor, to be successful, demands a certain objectivity, a slightly skewed point of view, an unexpected response to familiar events. This is what Confessions is unfortunately missing. Greenburg is to be commended--in this age of absentee fathers and child-support welshers--for his commitment to the responsibilities of parenthood and for the pleasure he seems to take in meeting them. One just wishes he'd waited awhile before sharing his enthusiasm with us.