Multiple Births in United States in 2006:

- Number of live singleton births:  4,121,930
- Number of live multiple births:        143,625

-Total number of births:                 4,265,555                           

- Number of twin births:             137,085  (2005 - 133,122)

- Number of triplet births:               6,118  (2005 - 6,208)

- Number of quadruplet births:          355  (2005 - 418)

- Number of quintuplets and

Births:  Final  Data  For  2006

From the CDC (Centers for Disease Control and Prevention) Website 

This is the most recent data on birth rate and associated trends in the United States. To view the entire report, click on this website: 

http://www.cdc.gov/nchs/data/nvsr/nvsr57/nvsr57_07.pdf

Here are some of the major statistics from this report:

In 2006, a total of 4,265,555 births were registered in the United States, 127,206 more births (or 3 percent higher) than in 2005. This is the largest single-year increase in the number of births since 1989-1990. After a downward trend from 1990 to 1997, the total number of births has generally increased. The number of births in 2006 is the largest since 1961 (4,268,326)

The number of births increased for all races and Hispanic origin groups between 2005 and 2006 with increases of 1 percent for non-Hispanic white, and 5 to 6 percent for non-Hispanic black and Hispanic women. Births to Asian or Pacific Islander and American Indian or Alaska Native women increased 4 and 6 percent, respectively. Among the specified Hispanic groups, births increased 4 to 6 percent for Mexican, Cuban, and Puerto Rican women and 9 percent for Central and South American women.

In 2006, there were 2,184,237 male and 2,081,318 female live births. There were 102,919 more male births, the highest number of ‘‘excess'' male births since 1963. The sex ratio, however, was the same as in 2005 at 1,049 males per 1,000 females.

There is considerable variation in the number of infants born on a given day of the week. In 2006, there was almost double the average number of births born on a Wednesday (13,482) than on a Sunday (7,587). In 2006, Wednesday, not Tuesday, became the most common day to deliver. Since at least 1990, the highest average number of births had occurred on Tuesday. An average of 11,686 infants was born each day in 2006.

In 2006, the average number of births per month increased significantly to 355,463 from 344,862 in 2005. The actual number of births occurring each month ranged from 319,235 in February, to 387,798 in August. Observed monthly birth and fertility rates, which take into account the different number of days in the month, increased significantly over the same month in the previous year for every month except April in which both birth and fertility rates declined. Observed fertility rates ranged from a low of 64.4 per 1,000 women aged 15-44 years in January to a high of 73.3 in August. The 2006 data showing fertility rates at their lowest in early winter and highest in late summer are consistent with well-established patterns of seasonal fluctuation in these rates.

The total cesarean delivery rate for 2006, 31.1 percent, is the highest level ever reported in the United States. This is a 3-percent increase from the 2005 rate.

Between 2005 and 2006 the total cesarean rate rose for women of all ages. As in past years, total cesarean rates increased with increasing maternal age. For example, the 2006 rate for mothers 40-54 years of age (47.6) was more than double the rate for mothers under age 20 years (22.2). The elevated rates for older mothers may be related to their increased rate of multiple births, other biologic or medical factors, and maternal or physician concerns.

Multiple Births

The rapid, unprecedented rise in multiple birth rates of the last several decades may have ended, at least temporarily. The 2006 twin birth rate was essentially unchanged for the second straight year at 32.1 per 1,000 births; this rate (births in twin deliveries per 1,000 births) had risen 70 percent from 1980 to 2004 (from 18.9 per 1,000). The rate of triplet and higher order multiple births (triplet/+) declined 5 percent in 2006, to 153.3 per 100,000 total births, from 161.8 in 2005. The triplet/+ rate (the number of triplets, quadruplets, and quintuplets and other higher order multiples per 100,000 live births) climbed more than 400 percent during the 1980s and 1990s, but has declined 21 percent since the all-time high in 1998 (193.5). Declines of 20 to 30 percent are observed in triplet/+ birth rates for women in age groups 25 years and over since 1998

.

Although the twin birth rate was essentially unchanged in 2006, the number of births in twin deliveries was up 3 percent for 2005-2006 to 137,085 births, another record high, and more than twice the number reported for 1980 (68,339). The number of triplet/+ births declined 2 percent from the previous year to the lowest reported in a decade (6,540 in 2006), and included 6,118 triplets, 355 quadruplets and 67 quintuplets. The number and rate of births in quadruplet and higher order deliveries have also declined in recent years.

The upsurge in multiple births, particularly higher order multiples, has been attributed to older age at childbearing (women in their thirties are more likely than younger women to conceive multiples spontaneously) and the growing availability and use of fertility-enhancing therapies (both assisted reproductive technologies (ART) such as in vitro fertilization), and non-ART therapies such as ovulation-inducing drugs and artificial insemination. Less than 20 percent of all triplets/+ born between 1997-2003 are estimated to have been naturally conceived (107,108). In response to the unparalleled rise in higher order multiple births and their attendant risk of poor outcome, The American Society of Reproductive Medicine published guidelines in the late 1990s (later updated), intended to reduce the incidence of triplets/+ resulting from ART by limiting the number of embryos transferred. Studies have since documented substantial declines in such transfers.

Triplet/+ birth rates declined between 2005 and 2006 for non-Hispanic white (208.1 per 100,000 in 2006) and non-Hispanic black (94.0) women; the downturn for Hispanics was not statistically significant (from 77.2 to 75.7). Between 1980 and 1998, large increases in triplet/+ birth rates were observed for each of these groups, but the most striking increase was among white mothers, up nearly 500 percent. Since 1998, triplet/+ birth rates have declined fairly steadily among non-Hispanic white women but, have fluctuated among non-Hispanic black and Hispanic women.

Twin birth rates were essentially unchanged among the three largest racial and Hispanic origin groups for 2005-2006; non-Hispanic white (36.0 per 1,000 in 2006), non-Hispanic black (36.8), and Hispanic (21.8). Since 1990, rates have risen 57 percent for non-Hispanic white, and 38 and 21 percent, respectively, for non-Hispanic black and Hispanic women.

Multiple birth rates tend to rise with increasing maternal age. This difference has widened in recent years with increases most pronounced for women 30 years and over. Between 1980 and 2006, twin birth rates rose 27 percent for mothers under age 20 years compared with 80 percent for women in their thirties, and 190 percent for mothers aged 40years and over. In 2006, 20 percent of births to women aged 45-54 years were  twins, compared with about 2 percent of births to women aged 20-24 years.

There is a high risk of an adverse outcome for multiple births. One out of every 8 twins, and one of every 3 triplets are born very preterm (less than 32 weeks of gestation), compared with fewer than 2 of every 100 singletons. Accordingly, death during infancy is much more common among twins (29.8 per 1,000) and triplets (59.6 per 1,000) than among singletons (6.0 per 1,000).

For years 2004 to 2006, twins accounted for more than 4 percent of all births (or more than 40 per 1,000) in Connecticut, Massachusetts, and New Jersey. In contrast, less than 2.5 percent of births to New Mexico residents were twins. The highest triplet/+ birth rates (over 250 per 100,000) were reported for Massachusetts, Nebraska, and New Jersey; the lowest, for New Mexico (72.3).

Numbers of twin, triplet, quadruplet, and quintuplet and other higher order multiple births: United States, 1990, 1995-2006

*Quintuplets, sextuplets and higher order multiple births are not differentiated in the national data set.