Can Triplets Be Identical?

Father holding his infant triplets

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Triplets are three babies carried in the same womb during a single pregnancy. Like twins, triplets and other higher-order multiples can be categorized by their zygosity or degree of genetic similarity. Though triplets are most commonly fraternal (dizygotic or trizygotic), it is possible for triplets to be identical (monozygotic).

How Identical Triplets Happen

While many people are familiar with the terms "identical" and "fraternal" in describing multiples and use them to describe whether twins or triplets look similar, what these terms actually refer to is how the multiples formed in utero. 

Monozygotic or identical multiples form from the same egg. In the case of identical twins, the fertilized egg splits in two. In the case of identical triplets, the egg may split just once into three or it may split twice (where the egg splits first in two and then one of the two splits again), resulting in three embryos with the same general DNA characteristics.

Monozygotic triplets are always the same sex, either all boys or all girls. Some monozygotic triplets are actually quadruplets where one embryo has vanished or been reabsorbed.

Odds of Identical Triplets

Research on the prevalence of monozygotic triplets varies. A 2012 case report of a healthy set of spontaneously conceived three identical triplet boys lists the incidence at 1 in 100,000 live births. Most reported cases are conceived through assisted reproductive techniques.

That paper noted that only seven other cases of spontaneously conceived identical triplets were known. A 2015 paper states the rate of incidence of identical triplets is 100 times more frequent with assisted reproductive techniques than spontaneous conception but is still extremely rare.

A monozygotic triplet pregnancy carries the risks of a monozygotic pregnancy with a shared placenta, plus the additional risks of a triplet pregnancy. A pregnancy of this type could be more likely to encounter problems such as preeclampsiapreterm labor, or transfusion syndrome.​ Other complications of which to be aware are gestational diabetes and fetal growth restriction.

How Fraternal Triplets Happen

Most triplets are trizygotic, meaning that each individual formed from a separate zygote, or egg and sperm combination. They are commonly described as "fraternal" multiples and share the same genetic similarities as any siblings.

However, it is not uncommon for triplets to be dizygotic, which occurs when two separate eggs are each fertilized, and one of the fertilized eggs then splits into two. Essentially, two of the triplets are monozygotic (identical) twins, sharing the same general DNA characteristics, while the third triplet having been conceived with a different egg and sperm has a unique genetic makeup from the other two.

Fertility and Multiples

According to a guide by the American Society for Reproductive Medicine (ASRM), multiple pregnancy is "more common in women who utilize fertility medications to undergo ovulation induction or superovulation." It also notes that among women who undergo fertility treatments, still less than 1% of them have triplets or other multiples.

Superovulation may be part of assisted reproductive technology treatments like in vitro fertilization (IVF). It means that multiple eggs are released through the use of fertility drugs, rather than a single egg that would usually be ovulated in the course of a menstrual cycle.

While multiple pregnancy is more common with medically assisted reproduction, twins, triplets, and higher-order multiples are still possible with naturally conceived pregnancies as well.

Pregnancy Signs of Triplets

There are a few pregnancy symptoms that could indicate you might be having triplets. These may include high levels of human chorionic gonadotropin (hCG) or alpha-fetoprotein in the blood, or severe morning sickness. But the only way to truly confirm multiple pregnancies is via ultrasound testing,

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3 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Gurunath S, Makam A, Vinekar S, Biliangady RH. Monochorionic triamniotic triplets following conventional in vitro fertilization and blastocyst transferJ Hum Reprod Sci. 2015;8(1):54–57. doi:10.4103/0974-1208.153131

  3. American Society for Reproductive Medicine. Multiple Pregnancy and Birth: Twins, Triplets, and High Order Multiples. 2012.