COMMITMENTS : The Sisterhood of Motherhood : There’s nothing that binds women together like pregnancy. It’s as if you’ve joined a secret club.

My father is fond of saying that pregnancy is a woman’s ideal state, both physically and emotionally. It’s a notion I’ve long pooh-poohed. After all, men who get fat, bloated and itchy for any amount of time, let alone nine months, never say they’re in a state of bliss.

But since I got pregnant, I must say my attitudes have changed. Suddenly, complete strangers--men and women--give me their places in line, they pump my gas when I’m in the self-serve station, they tote my luggage and refuse my tips, they say encouraging words when I take my daily walk and they smile at me for no reason.

Most importantly, I am suddenly friends with everybody who has ever had a baby. We’re talking about the kind of bonding that normally would take three lifetimes to achieve, especially in a large, anonymous city like Los Angeles.

“Someone once said to me, ‘You don’t have the secret handshake until you have a baby,’ and now that I’m in the club I see it’s so true,” said Katrina Sherer, mother of 9-month-old Natalie. “My best friend and I became best friends because of our pregnancies. We spoke every day.”

About what? wonder people who aren’t pregnant.

“Everything,” says Sherer’s best friend, Debra Collodel. “You’re obsessed with yourself and your pregnancy and people who aren’t pregnant, or haven’t been pregnant, just don’t get it. It’s just so much easier to be with other pregos.”

Who else, after all, can you truly vent with about itchy tummies, spreading stretch marks, stains on your face, perpetual exhaustion (try explaining to your male boss why you fall asleep on your desk) and a weight gain that extends beyond your belly.

What’s more, once you have that blasted baby, who else can understand that it takes a long while to get rid of the weight, that sex is never quite the same and that bladder control (horror of horrors) becomes a problem?

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Those were the issues that moved Vicki Iovine of Malibu to write “The Girlfriends’ Guide to Pregnancy” (Pocket Books, 1995).

Iovine, a first-time author and mother of four, believed that there was much more to pregnancy than a doctor could tell her.

“Doctors are wonderful, but the only cure for pregnancy is delivery,” she says. “I wanted to know why I got hair on my face, why my shoe size went up and why my butt grew before my stomach did.”

Apparently, a lot of people want to know such things, because Iovine’s book, which hit bookstores Sept. 5, is already in its second printing.

“I started collecting notes when my second child was 3 and I kept them for years,” says Iovine, wife of music industry executive Jimmy Iovine. “Women, including models and movie stars, told me the most intimate things. Complete strangers share birthing stories and we [women who have been pregnant] never get tired of hearing about it. I find that there’s a sorority, and to get into it you must be pregnant or have had a baby.”

The fact that it’s a sorority and not a sorority / fraternity might come as news to many well-intentioned husbands who try to be involved 100% in the pregnancy and delivery. But, hey, being there is just not the same as living it. And, as any pregnant woman knows, there is nothing more annoying than a man dishing advice on how to cope with your pregnancy just because he happened to be present during his wife’s ordeal.

Bottom line is, supportive husbands are great, but this is a woman’s show. Roxana Morini, mother of 2-year-old Aulo, likens it to the parting of the Red Sea.

“You walk into a party, and the room breaks in two: Pregnant women and new mothers on one side, everyone else on the other. The people you thought were incredibly boring before you got pregnant are now the most fascinating people in the room,” says the 35-year-old physician.

Which is not to say that all pregos are chums. There’s always someone who didn’t gain a pound more than necessary in those nine months, who didn’t get a single stretch mark or who wears a bikini and displays a washboard tummy a month after delivery. That’s great--unless she’s busy bragging about it to her less fortunate friends.

“I think women who brag are full of it,” says Iovine, who now is slim and petite but who swears she got huge with each pregnancy.

“There’s no such thing as a perfect pregnancy and the gods of pregnancy are usually fair. If you gained only 20 pounds, then you’ll probably get hemorrhoids,” she says dryly.

As for postpartum competitiveness, she adds: “Being a mom is not a contest. We’re all doing the best we can and we should be helping each other.”

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Some women are too busy doing other things to bond during pregnancy, some have no one to bond with and a few really don’t care.

“I was just concentrating on having my baby,” says Tunny Szpiros, mother of Olga, 5. “Making friends with someone just because they’re pregnant is great if it’s a coincidence, but why force it? Once I had my baby, however, I did everything possible to meet other moms.”

Being a mom is, after all, the ultimate hazing experience.

“Once you have that baby, you’re in,” Iovine says. “Unless, of course, you’re a horrible mother or you abandon your kid.”

Does this all mean your baby-less friends will be banished?

It depends on whom you ask. Some women, like Iovine, find that they have little to share with women who don’t have children. Others, like Szpiros, make a conscientious effort to keep up with all their friends equally, though undoubtedly, a mother will be more likely to understand why you’re pooped on a Saturday night than someone who has never had to wake up five times during the night to shush a screaming baby.

All of this, however, still seems light-years away to soon-to-be moms still navigating pregnancy. Just remember that no matter how terrible you feel or how awful you think you look, nearly everyone else will coddle you and say you’re wonderful, including that worldwide sorority of moms who have been there.

And if some woman--God forbid--has the audacity of doing something outright mean, like stealing your place in line while you were painstakingly waddling to get there, don’t dwell on it. Chances are, she hasn’t been pregnant, but when she is, she’ll remember you and weep.

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Top 10 Greatest Lies About Pregnancy

From “The Girlfriends’ Guide to Pregnancy” by Vicki Iovine (Pocket Books, 1995):

10. Lamaze works.

9. Morning sickness is gone by lunchtime.

8. Maternity clothes are so much cuter now.

7. You will have your pre-pregnancy figure back in three months, especially if you nurse.

6. Oil massages prevent stretch marks.

5. Pregnant women have the most beautiful skin and hair.

4. “I swear, your face hasn’t changed at all.”

3. Pregnancy brings a man and woman closer together. (Yeah--you and your obstetrician.)

2. “You haven’t gotten big anywhere but your belly.”

1. Pregnancy only lasts nine months.