In May 2021, the Cissé nonuplets were born in Morocco to Halima Cissé, a 25-year-old woman from Mali. As of May 2022, one year since their births, all nine 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 (Hellins law) and as about 1:80N−1. This gives:

1:89 (= 1.1%) or 1:80 (= 1.25%) for twins
1:892 (= 1:7921, about 0.013%) or 1:802 (= 1:6400) for triplets
1:893 (= approx. 0.000142%, less than 1:700,000) or 1:803 for quadrupletsNorth American dizygotic twinning occurs about once in 83 conceptions, and triplets about once in 8000 conceptions. US figures for 2010 were:
Twins, 132,562, 3.31%
Triplets, 5,503, 0.14%
Quadruplets, 313, 0.0078%
Quintuplets and more, 37, 0.00092%Human multiple births can occur either naturally (the woman ovulates multiple eggs or the fertilized egg splits into two) or as the result of infertility treatments such as in vitro fertilization (several embryos are often transferred to compensate for lower quality) or fertility drugs (which can cause multiple eggs to mature in one ovulatory cycle). 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 over the last decade.
Fetuses resulting from the same zygote share 100% of their genetic material and hence are called identical. Identical twins are always the same sex. 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
ten offspring – decupletsTerms used for multiple births or the genetic relationships of their offspring are based on the zygosity of the pregnancy:

Monozygotic – multiple (typically two) fetuses produced by the splitting of a single zygote
Polyzygotic – multiple fetuses produced by two or more zygotes:
Dizygotic – multiple (typically two) 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 fetusesMultiple pregnancies are also classified by how the fetuses are surrounded by one or more placentas (chorionicity) and amniotic sacs (amnionicity). Human multiple births
In humans, the average length of pregnancy (two weeks fewer than gestation) is 38 weeks with a single fetus. This average decreases for each additional fetus: to thirty-six weeks for twin births, thirty-two weeks for triplets, and thirty 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.