Is morning sickness a rite of passage? Find out why you might not have to deal with the nausea.

All the other moms-to-be are green with both nausea and envy--you've made it through your first trimester without even a hint of queasiness or a bout of vomiting. But without that queasy feeling, you might start wondering whether you're baby is A-OK in there.

But you can rest easy. "Nearly 30 percent of pregnant women completely skip out on any nausea," says Michele Hakakha, M.D., FACOG, an ob-gyn in Beverly Hills and author of Expecting 411. "And that's definitely something to be happy about."

So who are these lucky few who avoid the weeks-long nausea fests? Frankly, it could be anyone. "Some women may experience morning sickness, and some women may not; some women have it in one pregnancy and not the next," says Marra Francis, M.D., an ob-gyn in Woodlands, Texas, and a contributing author to the Mommy MD Guides. "Not everyone experiences morning sickness, just like not everyone gets motion sickness."

You may have a stronger constitution, one that's better able to handle the rapid rise in levels of hCG (human chorionic gonadotropin), estrogen, and other hormones that comes during the first trimester. Those levels spike quickly during pregnancy--the levels of hCG alone double every week during the first weeks of pregnancy--and, just like a quick ride on a roller coaster, this can make your stomach churn. Once you hit the second trimester, those hormone levels, while still increasing, taper off to a more manageable level.

In a few women, a lack of morning sickness could indicate that their hormone levels are much lower than normal and that they're at increased risk of a miscarriage, but that is usually not the case--and you definitely should not worry if you're not feeling any morning sickness, as long as your ob-gyn thinks your hormone levels look good. "I've had women who freaked out because they didn't get morning sickness, because they thought they were at higher risk of having a miscarriage," Dr. Francis says. "But if you don't have morning sickness, it doesn't mean that you have abnormal hormone levels; it just means that you tolerate [pregnancy] better."

But don't get too complacent! Even if you're out of your first trimester, you may not be out of the woods. Although most women get their morning sickness between weeks 8 and 14, every woman and every pregnancy is different, and you may find that you develop pregnancy-related sickness later.

If you're nausea-free, consider yourself lucky-and enjoy the fact that you can get through what's often one of the toughest trimesters of pregnancy without too much trouble.