BALTIMORE -- Expecting her first child, Qwanda Joines becomes a little more confident with every ultrasound.

The 27-year-old mother is expecting a boy, but early in her pregnancy she discovered she was having twins.

Then, almost as quickly as she found out, one of them was gone.

Dr. Robert Atlas, the chairman of Mercy Medical Center's Department of Obstetrics and Gynecology, said the rate of live twin births is about one in 80 pregnancies. But the actual incidence of twinning is much higher -- about one in eight pregnancies.

"Vanishing twin syndrome is a phenomenon that occurs much more commonly in pregnancy than we think," he said.

Vanishing twin syndrome denotes a twin who disappeared sometime during the mother's pregnancy. In fact, many women don't ever know they're carrying twins.

So, what happens to that other fetus?

"In very early losses, it just dissolves and you may have associated bleeding," Atlas said.

There's very little risk of complications for the surviving twin or mom.

"We do get worried about women who have losses in the second and third trimester (when there's) much higher risk and much higher concern for those babies," Atlas said.

Among the possible complications for the surviving twin include cerebral palsy, and for the mother, preterm labor or infection.

Joines lost her twin early in her second trimester, but the surviving twin is thriving.

"He's doing good. Every time I get scared, I come down and get an ultrasound. I'm hearing nothing but wonderful things," she said.

There's no clear cause for vanishing twin syndrome, but advancing ultrasound technology has allowed doctors to identify it more often.

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