Multiple Pregnancy

Too Much of a Good Thing?

By Michele St. Martin

They're so cute! Two or three, just alike or similar enough so you can tell that they're twins or triplets. But it's not all sweet-smelling babies and identical clothing: multiple pregnancies are considered high-risk, and the more fetuses the mother is carrying, the higher the risk to both her and her unborn children. And with more women taking advantage of advanced reproductive technology (ART) and fertility drugs, multiple pregnancies and births are skyrocketing, according to the National Center for Health Statistics.

While the vast majority of these pregnancies (94 percent in 1997) are twins, the rates for triplets and other higher-order multiples are growing at an even faster rate. According to a paper published by Dr. Louis Keith, Susan Klock, Ph.D. and Dr. Sanjay Gandhi, "In little more than two decades, the subject of multiple pregnancy has evolved from an obstetric curiosity to an issue of international medical and social concern."

About two-thirds of twins are not identical. Commonly called fraternal twins, the correct scientific term for these twins is dizygotic. Dizygotic twins are the result of two separate eggs being ovulated and fertilized at the same time by two different sperm, thus giving these twins each a different genetic makeup.

Twins who share the same genetic makeup are commonly referred to as identical twins, though the correct scientific name for these twins is monozygotic. Identical twins are conceived when an egg, fertilized by one sperm, divides into two separate embryos. Identical twins not only usually look alike, they also are always of the same sex and blood type. While in the womb, they share the same placenta.

According to the National Center for Health Statistics, the number of twins born increased from more than 68,000 in 1980 to more than 104,000 in 1997.

While twinning rates have increased for all age groups, the increases were most dramatic among women 30 and over (the age group most likely to take advantage of ART). Twin birth rates increased by 41 percent for women in their 30s, by 63 percent for women 40 to 44 years old and by nearly 1,000 percent among women 45 to 49 years of age. Most of the women in this last age group used donor ovum (eggs donated by younger, fertile women). There were more twins born to women ages 45 to 49 in 1997 than during the entire decade of the 1980s.

Want to see more?

• Our Experiences With Twins
• High Tech Babies: In-vitro Fertilization
• You're Pregnant With Twins Now Keep Those Babies in There!
• Two at Once: Pregnant With Twins
• Talk about it!