John Travolta and Kelly Preston
Photo from Splash News

The next natural reaction after shock, happiness, and wonder at reports that John Travolta's 47-year-old wife Kelly Preston is three months pregnant, assuming it really is true, is to ask a slew of big questions, the first of which is:

What is the chance a 47-year-old could even get pregnant!?

Women over 45 can and do, of course. There were 7,666 live births to women 45 to 54 in 2008 in the United States alone, and just days ago, news that a 54-year-old Italian woman who thought she was going through menopause discovered she had conceived naturally.

But that's really not a lot. No one has to tell us how rare it truly is, and that the odds of getting pregnant in your early 40s, let alone your late 40s, is difficult enough.

Women over 40 have just a 5 percent chance of getting pregnant each month -- and that includes both the natural way and through assisted reproduction, including artificial insemination and with in-vitro fertilization, according to the American Society for Reproductive Medicine.

They don't even track the stats for women over 45,but you can bet the chance of pregnancy dwindles even more.

So Preston really did defy the odds. Awesome for her. She gives so many other women hope. But the second big question with an older pregnancy is ...

What about birth defects?

Many moms have been through the horror of genetic blood testing and ultrasounds when the doctor gives the obligatory rundown of odds of Down syndrome and other chromosomal abnormalities based on the mother's age.

When I got pregnant with my children in my 30s, the risk of my baby being born with Down syndrome was 1 in 378 and 1 in 192 for Down and all other chromosomal problems lumped together. Those didn't sound like great odds to me. At all. I worried a lot, especially when I learned how much better it would have been had I conceived in my 20s: 1 in 1,250 for Down and 1 in 476 total chromosomal.

When Sarah Palin, another notable over-40 mom, got pregnant with son Trig at age 43, her risk of a Down syndrome baby was 1 in 49 and 1 in 43 total. Trig was born with Down syndrome.

IVF may help to control some abnormalities before implantation -- at Preston's age of 47, the risk of those kinds of birth defects rises to 1 in 18 and 1 in 14!

There's a very good chance Preston used an egg donor, an option that many other women choose to avoid the possibility of a baby born with birth defects. There really are so many variables, and until the Travolta-Prestons tell us more, all we can do is speculate.

Because the eggs of older women are less likely to develop, someone Preston's age is also more likely to miscarry -- a 53 percent chance of what is referred to as a spontaneous abortion -- than, say, a woman in her 20s to mid-30s who has a 10-12 percent chance.

This is not meant to be a downer, but an important reminder of how much harder it is to be a mom at an older age. I hope more than anything that Preston continues to defy all the odds and enjoys a complication-free pregnancy ending with a healthy and thriving baby. After all they've been through in the last year, she and her family deserve it.

Are you an older mom? Are you worried about the increased risks?