Multiple birth
A multiple birth is the culmination of a multiple pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets. In non-humans, the whole group may also be referred to as a litter, and multiple births may be more common than single births. Multiple births in humans are the exception and can be exceptionally rare in the largest mammals.
A multiple pregnancy may be the result of the fertilization of a single egg that then splits to create identical fetuses, or it may be the result of the fertilization of multiple eggs that create fraternal fetuses, or it may be a combination of these factors. A multiple pregnancy from a single zygote is called monozygotic, from two zygotes is called dizygotic, or from three or more zygotes is called polyzygotic.
Similarly, the siblings themselves from a multiple birth may be referred to as monozygotic if they are identical or as dizygotic or polyzygotic if they are fraternal, i.e., non-identical.
Each fertilized ovum may produce a single embryo, or it may split into two or more embryos, each carrying the same genetic material. Fetuses resulting from different zygotes are called fraternal and share only 50% of their genetic material, as ordinary full siblings from separate births do. Fetuses resulting from the same zygote share 100% of their genetic material and hence are called identical. Identical twins are almost always the same sex, however in rare circumstances, chromosomal mutations can lead to different sexes being expressed.
Terminology
Terms used for the number of offspring in a multiple birth, where a number higher than three ends with the suffix -uplet:- two offspring – twins
- three offspring – triplets
- four offspring – quadruplets
- five offspring – quintuplets
- six offspring – sextuplets
- seven offspring – septuplets
- eight offspring – octuplets
- nine offspring – nonuplets
- Monozygotic – multiple fetuses produced by the splitting of a single zygote
- Polyzygotic – multiple fetuses produced by two or more zygotes:
- * Dizygotic – multiple fetuses produced by two zygotes
- * Trizygotic – three or more fetuses produced by three zygotes
- * Sesquizygotic – an egg which is fertilized by 2 sperms, which produce 2 fetuses
Human multiple births
In humans, the average length of pregnancy is 38 weeks with a single fetus. This average decreases for each additional fetus: to 36 weeks for twin births, 32 weeks for triplets, and 30 weeks for quadruplets. With the decreasing gestation time, the risks from immaturity at birth and subsequent viability increase with the size of the sibling group. Only as of the twentieth century have more than four all survived infancy.Recent history has also seen increasing numbers of multiple births. In the United States, it has been estimated that by 2011, 36% of twin births, and 78% of triplet and higher-order births resulted from conception by assisted reproductive technology.
Twins
Twins are by far the most common form of multiple births in humans. The U.S. Centers for Disease Control and Prevention report more than 132,000 sets of twins out of 3.9 million births of all kinds each year, about 3.4%, or 1 in 30. Compared to other multiple births, twin births account for 97% of them in the US. Without fertility treatments, the probability is about 1 in 60; with fertility treatments, it can be as high as 20-25%.Dizygotic twins can be caused by a hyperovulation gene in the mother. Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them.
Monozygotic twins do not run in families. The twinning is random, due to the egg splitting, so all parents have an equal chance of conceiving identical twins.
Triplets
Triplets can be either fraternal, identical, or a combination of both. The most common are strictly fraternal triplets, which come from a polyzygotic pregnancy of three eggs. Less common are triplets from a dizygotic pregnancy, where one zygote divides into two identical fetuses, and the other does not. Least common are identical triplets, three fetuses from one egg. In this case, sometimes the original zygote divides into two and then one of those two zygotes divides again but the other does not, or the original zygote divides into three.Triplets are far less common than twins, according to the U.S. Centers for Disease Control and Prevention, accounting for only about 4,300 sets in 3.9 million births, just a little more than.1%, or 1 in 1,000. According to the American Society of Reproductive Medicine, only about 10% of these are identical triplets: about 1 in ten thousand. Nevertheless, only 4 sets of identical triplets were reported in the U.S. during 2015, about one in a million. According to Victor Khouzami, Chairman of Obstetrics at Greater Baltimore Medical Center, "No one really knows the incidence".
Identical triplets or quadruplets are very rare and result when the original fertilized egg splits and then one of the resultant cells splits again or, even more rarely, a further split occurs. The odds of having identical triplets is unclear. News articles and other non-scientific organizations give odds from one in 60,000 to one in 200 million pregnancies.
Quadruplets
Quadruplets are much rarer than twins or triplets. As of 2007, there were approximately 3,556 sets recorded worldwide. Quadruplet births are becoming increasingly common due to fertility treatments. There are around 70 sets of all-identical quadruplets worldwide. Many sets of quadruplets contain a mixture of identical and fraternal siblings, such as three identical and one fraternal, two identical and two fraternal, or two pairs of identicals. One famous set of identical quadruplets was the Genain quadruplets, all of whom developed schizophrenia. Quadruplets are sometimes referred to as "quads".Quintuplets
Quintuplets occur naturally in 1 in 55,000,000 births. The first quintuplets known to survive infancy were the identical female Canadian Dionne quintuplets, born in 1934. Quintuplets are sometimes referred to as "quins" in the UK and "quints" in North America. A famous set of all-girl quintuplets are the Busby quints from the TV series OutDaughtered.Sextuplets
Born in Liverpool, England, on November 18, 1983, the Walton sextuplets were the world's first all-female surviving sextuplets, and the world's fourth known set of surviving sextuplets. Another well-known set of sextuplets is the Gosselin sextuplets, born on May 10, 2004, in Hershey, Pennsylvania. Reality television shows Jon & Kate Plus 8 and later Kate Plus 8 have chronicled the lives of these sextuplets. Other shows of this nature include Table for 12 and Sweet Home Sextuplets.Very high-order multiple births
In 1997, the McCaughey septuplets, born in Des Moines, Iowa, became the first septuplets known to survive infancy. The first surviving set of octuplets on record are the Suleman octuplets, born in 2009 in Bellflower, California. In 2019, all 8 children celebrated their 10th birthday. Multiple births of as many as 9 babies have been born alive; In May 2021, the Cissé nonuplets were born in Morocco to Halima Cissé, a 25-year-old woman from Mali., two years since their births, all 9 are still living and reportedly in good health.The list of multiple births covers notable examples.
Causes and frequency
The frequency of N multiple births from natural pregnancies has been given as approximately 1:89N−1 and as about 1:80N−1. This gives:- 1:89 or 1:80 for twins
- 1:892 or 1:802 for triplets
- 1:893 or 1:803 for quadruplets
- Twins – 132,562
- Triplets – 5,503
- Quadruplets – 313
- Quintuplets and more – 37
For reasons that are not yet known, the older a woman is, the more likely she is to have a multiple birth naturally. It is theorized that this is due to the higher level of follicle-stimulating hormone that older women sometimes have as their ovaries respond more slowly to FSH stimulation.
The number of multiple births has increased since the late 1970s. For example, in Canada between 1979 and 1999, the number of multiple birth babies increased 35%. Before the advent of ovulation-stimulating drugs, triplets were quite rare and higher-order births much rarer still. Much of the increase can probably be attributed to the impact of fertility treatments, such as in-vitro fertilization. Younger patients who undergo treatment with fertility medication containing artificial FSH, followed by intrauterine insemination, are particularly at risk for multiple births of higher order.
Certain factors appear to increase the likelihood that a woman will naturally conceive multiples. These include:
- mother's age: women over 35 are more likely to have multiples than younger women
- mother's use of fertility drugs: approximately 35% of pregnancies arising through the use of fertility treatments such as IVF involve more than one child
The increasing use of fertility drugs and consequent increased rate of multiple births has made the phenomenon of multiples more frequent and hence more visible. In 2004 the birth of sextuplets, six children, to Pennsylvania couple Kate and Jon Gosselin helped them to launch their television series, originally Jon & Kate Plus 8 and Kate Plus 8, which became the highest-rated show on the TLC network.