Multiple birth

A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies.

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 ("non-identical") fetuses, or it may be a combination of these factors.

Fetuses resulting from different zygotes are called fraternal and share only 50% of their genetic material, as ordinary full siblings from separate births do.

[3] With the decreasing gestation time, the risks from immaturity at birth and subsequent viability increase with the size of the sibling group.

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.

[11] 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.

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.

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.

[33] Drugs known as betamimetics can be used to relax the muscles of the uterus and delay birth in singleton pregnancies.

[34] There is some evidence that these drugs can also reduce the risk of preterm birth for twin pregnancies, but existing studies are small.

[35] Likewise, existing studies are too small to determine if a cervical suture is effective for reducing prematurity in cases of multiple birth.

Premature birth is associated with a higher risk for a breadth of behavioral and socioemotional difficulties that begin in childhood and continue through teenagehood and often into adulthood.

[39] Multiples may be monochorionic, sharing the same chorion, with resultant risk of twin-to-twin transfusion syndrome.

This shows that stillbirth happens usually 3–5 weeks before the woman reaches full term and also that for sextuplets or higher it almost always ends in death of the fetuses.

In a 1997 study of 2,173 embryo transfers performed as part of in vitro fertilisation (IVF), 34% were successfully delivered pregnancies.

[47][48] Selective reduction was developed in the mid-1980s, as people in the field of assisted reproductive technology became aware of the risks that multiple pregnancies carried for the mother and for the fetuses.

[52] Evidence around this subject is not yet good enough to advise women to do this because the long term effects of the high-calorie diets on the mother are not known.

[53] A study in 2013 involving 106 participating centers in 25 countries came to the conclusion that, in a twin pregnancy of a gestational age between 32 weeks 0 days and 38 weeks 6 days, and the first twin is in cephalic presentation, planned Cesarean section does not significantly decrease or increase the risk of fetal or neonatal death or serious neonatal disability, as compared with planned vaginal delivery.

[54] In this study, 44% of the women planned for vaginal delivery still ended up having Cesarean section for unplanned reasons such as pregnancy complications.

[56] Fetal position (the way the babies are lying in the womb) usually determines if they are delivered by caesarean section or vaginally.

[58] The birth of this type of twins should therefore be decided with the mother and her family and should take into account the need for good neonatal care services.

Kaufman found from reviewing these files that during a five-year period, 55 triplet pregnancies (i.e. 165 babies) were delivered.

In Greek mythology, fraternal twins Castor and Polydeuces, and Heracles and Iphicles, are sons of two different fathers.

In certain medieval European chivalric romances, such as Marie de France's Le Fresne, a woman cites a multiple birth (often to a lower-class woman) as proof of adultery on her part; while this may reflect a widespread belief, it is invariably treated as malicious slander, to be justly punished by the accuser having a multiple birth of her own, and the events of the romance are triggered by her attempt to hide one or more of the children.

Out of all the assisted reproductive technology available that is currently in practice, in vitro fertilization has the highest chance of producing multiple offspring.

However, in vitro can become genetically specific and allow for the selection of particular genes or expressible traits to be dominantly present in the formed embryo.

[64] Ethical dilemmas arise when determining health care coverage and the deviation from natural selection and gene variations.

[66] While some view medically assisted procreation as a saving grace to have children, others consider these procedure to be unnatural and costly to the community.

The overarching purpose of the procedure is not primarily to simply terminate life, but to increase the survival and success of the mother and babies.

The protection of maternal well being versus harm of newly formed fetal life is an extension of the aforementioned ethical question.