The stain (known as "mehndi") on the skin will go away in a few days to a couple of weeks in most people. It's often done on the hands and feet as well.
The intent of doing henna art in pregnancy was originally to protect the child. Quoting from the Henna Caravan website:
Lawsonia Inermis or henna is a small bush that produces a red dye that has been used cosmetically and medicinally for over 9,000 years. Many countries including Morocco and India have traditions of applying henna during the third trimester of pregnancy. Henna is believed to protect and bless the mother and child from any evil or malicious spirits that may be near during delivery. The red coloring of the dye and protective images used in the patterns guard against the evil eye and are thought to protect the pair during the child's difficult passage into this world.Here's how getting a henna tattoo works.
Henna powder (ground from the dried leaves of the henna plant) is combined with lemon juice, sugar, and essential oils (like lavender) and made into a paste, then applied onto the skin in decorative patterns. The paste must be left on for several hours.
At some point after the paste is dry, most henna artists have you come back to "seal" the design by applying lemon sugar syrup, pump spray hair gel, or liquid bandage, etc. The longer the paste can be kept on, the better the tattoo. Eventually, however, the paste rubs off, leaving the "tattoo" behind.
There are a few precautions to be aware of. You want to make sure your artist uses only benign ingredients; occasionally some artists add unsafe chemicals or use "black" henna (which is really PPD, para-phenylendiamin, a.k.a. black hair dye) instead of true henna. These can cause blistering or other problems. Always ask the artist what is used in their henna paste before agreeing to a tattoo.
According to some websites, henna artwork should be avoided in women who are extremely anemic or women whose babies have G6PD deficiency or hyperbilirubinemia. Any woman who has had (or who has had a child who has had) a chronic or acute condition affecting the blood system or immune system should also not receive henna. Other than that, though, belly art with henna is thought to be a very low-risk decorative option.
I've had henna done on my hands in recent years, but seeing how lovely these henna tattoos came out, I sure wish I'd known about it during my childbearing years! Way cool. Would have been fun during a blessingway ceremony.
Just another way you can celebrate your belly and your baby during pregnancy!! (And who's to say it has to be limited only to pregnancy!)
*Thanks to Angela and Stacy, both women of size, for sharing their henna pictures with us.
Here are some more links about henna for pregnant bellies:
http://www.hennacaravan.com/pregnancy.html - general information about henna in pregnancy
http://www.shophenna.com/GalleryBelly.htm - pictures of various belly henna designs
http://www.hennapage.com/henna/what/freebooks/HPJpp2.pdf - e-book about henna traditions postpartum
http://www.hennapage.com/henna/encyclopedia/pregbirth/index.html - info and pictures
http://www.castingkeepsakes.com/pregnancy-henna-art-kit-p-217.html - a kit you can order
http://www.icnha.org - organization of certified henna artists
http://www.hennapage.com/ - information about henna use in general
http://hennadenver.com/henna-faq/ - info about henna for pregnancy