Seems everywhere you look, someone’s having twins. That’s because they are. According to a report from the National Center for Health Statistics, the rate of twin births rose 76 percent from 1980 to 2009. In 2009, 1 in every 30 babies born in the United States was a twin, compared with 1 in every 53 babies in 1980.
Massachusetts is the state with the highest rate of twinning.
The report states that twin birth rates increased for women of all ages over the past three decades, with the largest increases among women older than 30. Rates increased 76 percent for women aged 30 to 34, nearly 100 percent for women aged 35-39 and a whopping 200 percent for women 40 and older.
Some of the increase can be chalked up to the fact that women are waiting longer to have their families. And being older than 30 increases the chance of having twins. An online study appearing in Human Reproduction showed that older women had higher levels of FSH (follicle-stimulating hormone) and were more likely to release more than one egg per menstrual cycle. They’re also at greater risk for infertility problems and of resorting to in vitro fertilization (IVF) treatments in order to conceive.
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But age isn’t the only factor. Diet plays a role, too. A study conducted by Dr. Gary Steinman and published in the Journal of Reproductive Medicine found that women who consume animal products — especially dairy — were five times more likely than vegans to have twins. Milk drinkers had 13 times more IGF (insulin-like growth factor), a protein that triggers ovulation.
That same protein stimulates bone growth and may explain why tall women give birth to more twins, Steinman said in a separate study published in the same journal.
Steinman also found that women who become pregnant while breastfeeding are nine times more likely to conceive twins than women who aren’t breast-feeding.
There’s even a twin gene. If a woman inherits a particular gene that causes her to hyper-ovulate (release more than one egg at a time) she is predisposed to having twins. She can also pass that gene on to her offspring. Men inherit the gene, too, but only their daughters will bear the twins. That may explain why twins tend to skip generations.
Genetics only applies to fraternal — not identical — twins. There’s no known gene that causes an egg to split in half. So identical twinning isn’t heredity.
Twins themselves are captivating. An amazing 22 percent of certain types of twins are left-handed, compared with 10 percent of the general population. And 40 percent of them (mostly identical twins) develop their own language, known as idoglossia, or twin talk.
Far more twins are conceived than are actually born. The vanishing twin syndrome occurs when a twin or multiple disappears in the uterus during pregnancy as a result of a miscarriage of one fetus. It is usually detected by an ultrasound. The fetal tissue is absorbed by the other twin, the placenta or the mother. The American Pregnancy Association website estimates that it occurs in 21 to 30 percent of all multifetal pregnancies.