Britney can dance, but does she do diapers?

So Britney Spears is pregnant.

As the mother of three daughters all I can say is that I hope this won’t spark another fashion trend. I’ve battled the midriff-baring shirts and the super low-rise jeans since Spears put them on the style map. The last thing we need is young girls everywhere saying, “I want a big belly just like Britney’s.”

In Britney Spears’ world, it’s fashionable to have a baby. It’s also fashionable to carry a Chihuahua in your purse. I just hope Spears knows the difference.

Do they cover that sort of thing in parenting classes held especially for the overindulged and self-absorbed MTV glitterati?

“The first thing you need to realize,” the serene and stylish class facilitator would warn, “is that it’s not about you anymore. From now on you’ll get second billing.”

After the gasps and shocked cries subsided, the leader would have to break the big news. “Mothering isn’t like, you know, a sold-out tour.”

But even for those of us with both feet rooted firmly in the middle class it comes as a surprise to discover that the soft, cherubic, babies of our imagination are born with their own agenda. Instead of pretty playthings, real children are unpredictable, inconvenient and frequently messy.

I can’t help but think that Spears doesn’t have a clue that the baby she’s cooing about now will eventually wet, poop and throw up on her – all on the same day.

It will cry and cling to her when she wants a night out. A baby may even require more time and energy than a Chihuahua.

In a culture of eternal youth and ageless beauty, like Spears’ world, it has to come as a shock that babies make their marks on us before they’re even born. And afterward other changes are revealed. Curves get wider and gravity gets a helping hand. For someone with Spears’ penchant for exposure, it’s going to be a big deal when perky breasts that once fit snugly into a 36D, look like a size 36 Long after the baby comes.

Last year, the tabloids had a field day with photos of Spears padding in and out of a public restroom in bare feet. Ick.

Well, if it’s too much trouble to put her own shoes on, she’s not going to believe how hard it is to dangle a wriggling little girl, who’s in no mood to cooperate, over a nasty public toilet, or to help a little boy control his, um, aim – for your own protection – in a tiny stall.

Spears may not realize just how much having a baby may alter her personal style. But when the little one gets hold of that belly ring she likes to flash, she’ll find out why it’s possible to lead a stubborn 1,500 pound bull around by the ring in his nose: Because it hurts.

Now that she’s gotten her wish and a baby is on the way (the only thing she hasn’t already done at the ripe old age of 23,) Britney will have to learn for herself that in spite of the pain and the trouble, the stretching and sagging, and the fact that from the moment your child is born the spotlight will never again shine as brightly on you, motherhood is good work. But it’s hard work.

If pre-natal classes for spoiled young celebrity mothers-to-be don’t exist, someone will have to teach Britney that you can’t play mommy to a real baby the way you can to a Chihuahua. And you can’t pose, or wriggle and dance your way through it.

Mothering is a real job. It hurts, and it transforms you. And unlike perky breasts, screaming fans and a sold-out world tour, it lasts forever.