Thirty-one years ago, my daughter, Zoe, was born. I was ecstatic. But it wasn't just about the baby. I was almost as excited to mark the end of the most miserable nine months of my life -- or, as it will be known from this point forward, the Princess Pregnancy. (Kate is actually a duchess; there's just something about the word "princess.")In 1980, hyperemesis gravidarum was, at best, a royal pain in the neck. I had heard of morning sickness. At first, if anything, it was a relief, proof positive that there really was a baby in there. That was until morning sickness set in 24/7 throughout my entire pregnancy.Which is why Zoe's birthday was cause for double celebration. No more throwing up, getting dehydrated and ending up in the hospital on IVs. No more concerned friends suggesting burnt toast or vitamin B shots or sharing stories of starved women in concentration camps whose babies came out fine. No more doctors suggesting that perhaps I was ambivalent about giving up my freedom or, worse, a hypochondriac.I had been thrilled about being pregnant. I may as well have had the plague. Forget glowing: Just getting out of my ratty robe and into real clothes was a remarkable feat. Plus, I felt guilty that my husband's life had been reduced to running back and forth to the hospital while moonlighting, since I was too sick to work.On the positive side, for me, pregnancy was a radicalizing event. For starters, there was my doctor, who had the gall to suggest that my round-the-clock sickness was a function of being ambivalent about motherhood. I told him I wanted a baby, couldn't wait to be a mother -- I just wanted my head out of the toilet, if that wasn't too much to ask.Which led to Insult No. 2: Was I bulimic? Maybe I was symbolically trying to "throw up the baby." I assured him that I had never been bulimic, couldn't remember the last time I was nauseated, but was starting to feel like throwing up, especially when he referred me to a psychiatrist who grilled me on my relationship with my own mother, my feelings about femininity, and -- surprise! -- my sex life. Turned out his doctoral thesis was on the pathology of women who choose to be child-free. I finally understood what feminists referred to as their "rage stage."But that was only one side of how my pregnancy was life-changing. Being as vain as the next girl, I cared a lot about how I looked. I had been a chubby teenager, but, now, each pound gained was a triumph. For the first time I could, and did, eat anything I wanted, which would have been great had I been able to keep it down. And then there were those matronly maternity clothes. We're talking Pre-Sweatpants. In 1980 the idea was to keep pregnancy literally under wraps, wearing smock tops and tent dresses, which several women I knew burned once their baby was born.This is one issue Kate will not have to deal with. Think Demi Moore on the cover of Vanity Fair: a proud pregnant woman sunning in a bikini, wearing her baby like a beautiful full moon.But even when maternity clothes were more function than fashion, I loved them. It didn't matter that they were ugly or shapeless; instead of seeing my body as a "clothes hanger," I now stared at my swollen belly in awe, amazed at the miraculous evidence of my baby's development. I was growing a baby! Making a fashion statement paled beside the greatest miracle on earth.None of which negates the severe hyperemesis that is headline news now that Kate is bearing the next royal baby. I'm a bit envious when I think back to how defensive I felt about being less than a "perfect pregnant woman." It won't take away the nausea or fear, but Kate's ordeal will change perceptions of this serious medical condition.What Demi did on the fashion front, Kate will do for expectant mothers having difficult pregnancies.Here's what I'd tell her: Your baby will be fine. You will feel better, and even if it takes nine months, it will be well worth it. Because becoming a mother doesn't just happen. Being a princess -- OK, a duchess -- is big. Global, paparazzi, the-future-of-England big. But carrying a child is bigger. Whether you're royalty or the girl next door, nothing you do will ever be quite this momentous.Ellen Sue Stern is author of "Expecting Change: The Emotional Journey Through Pregnancy."