There was a time when you couldn’t say the word “pregnant” on radio or television. Now shows about expectant mothers have become a growing niche of cable programming. The miracle of birth and its eventful anticipation seems to make for natural drama. After all, it has a beginning, a middle and an end, which can be seen as either another beginning, or a bit of an anti-climax. Wasn’t it Bob Dylan who once sang, “He not busy being born is busy dying”?

The stork frenzy continues tonight with “I Didn’t Know I Was Pregnant” (8 p.m., TLC) about women who conceive and carry their babies to term without ever developing a clue. Or even an inkling. In the words of the famous Rodgers and Hart song, “It Never Entered My Mind.”

The fascinating, or repellent, aspect to “I Didn’t Know” is that it’s not merely a squeamish special from TLC, the home to shows about sextuplets, cakes and little people, but a series. An entire series.

Will people tune in week after week to gawk at the obstetrically challenged? Well, if there was an audience for last year’s TLC documentary “Purity Balls,” there’s a demographic for this, too. The same niche that won’t miss “Obese and Pregnant” (9 p.m., TLC), I presume. This all makes “16 and Pregnant” (6 p.m. and 7 p.m., MTV) seem so run of the mill.

l Apparently on PBS, the stuff of history is stuff itself. “Antiques Roadshow” teaches the price of things and value of not over-varnishing. “History Detectives” shows that artifacts forgotten in our dusty drawers and attics can offer a window on an unexplored past. And tonight, “Time Team America” (7 p.m., PBS) sends archaeologists to some of the nation’s most important historical sites.

Tonight’s team visits Roanoke Island to ponder one of the more enduring mysteries of American history: the fate of the first British colony in the New World.

l The documentary “The Conscience of Nhem En” (7 p.m., HBO2) explores the story of the Cambodian genocide through one man’s story. As a 16-year-old, he recalls, he joined the murderous Khmer Rouge for two basic reasons: “to live and to eat.” He was assigned to photograph and register thousands of victims of the terror as they entered a Phnom Penh prison, from which only a handful emerged. They were tortured so that they would confess to working for either the CIA or the KGB, and then murdered anyway.

He bristles at the notion that he was part of any crimes against his own people. He sees himself as a survivor and someone who created a record of the victims for posterity. This is not an easy film to watch.

Tonight’s other highlights

l Two helpings of “America’s Got Talent” (7 p.m., NBC).

l “So You Think You Can Dance” (7 p.m., Fox) continues for two more hours.

l “Ghost Hunters International” (8 p.m., Syfy) visits Wicklow, Ireland. Repeats air at 7 p.m. and 9 p.m.

l A trip to Paris leads to information about a nefarious trade on “The Philanthropist” (9 p.m., NBC).

l Scheduled on “Primetime” (9 p.m., ABC): a brutal assault at a Texas university.

l A murdered Palestinian becomes an organ donor on “Wide Angle: Heart of Jenin” (9 p.m., PBS, check local listings).