Multiple pregnancy can be fascinating. The idea of carrying another life inside you itself is amazing, let alone carrying two or more lives at the same time. Well, this is going to get even more interesting now as we are about to dive deep into the world of the rarest medical occurrings and bring to light a phenomenon that is going to leave you awestruck. We are talking about Heteropaternal Superfecundation, which refers to carrying twins, each conceived from the sperm cell of a different man. 

What is Heteropaternal Superfecundation?

‘Heteropaternal’ means ‘different fathers’, whereas ‘Superfecundation’ means ‘fertilization of multiple eggs during the same menstrual cycle’. This means that the offspring have the same mother but different fathers. The rare phenomenon occurs when a woman releases not one, but two eggs in her monthly cycle, which then get fertilized by sperm cells from two different males. For this, it is crucial that the female has intercourse with two different partners within a short span of time. The phenomenon may seem new but it has been mentioned in ancient Greek and Roman Mythology, where a mortal woman had intercourse with a male god and a mortal male on the same day, resulting in the birth of babies fathered by different males, as in the cases of Helen of Troy and Hercules. 

“Heteropaternal Superfecundation is a very rare condition that has the potential to cause intense emotional trauma to the parents as well as the children in the future. Such situations need to be dealt with empathetically considering the impact they may have. It demands a multidisciplinary approach involving a family doctor, psychiatrist, psychologist, and family counselor.” -  Dr. Janardhan Reddy - Pediatrician

How Common is Heteropaternal Superfecundation

Heteropaternal Superfecundation is extremely rare in humans and it is quite difficult to estimate the numbers as it usually goes undiscovered unless paternity is challenged due to one reason or the other. To make it more simple, 

The chances of having twins are approximately 1 in 250 

Among these, the chances of having fraternal twins are around 70 percent

Out of these 70 percent, the chances of having Heteropaternal Superfecundation twins are merely 2.4 percent. 

What leads to Heteropaternal Superfecundation?

Every pregnancy starts with the process of fertilization. This happens when the male and female gametes (the egg and the sperm) come together. Women usually release one egg every month and this gets fertilized by a single healthy sperm from the pool of sperm coming from the male partner. 

In the case of twin pregnancy, which is relatively uncommon, a woman either releases two eggs then fertilized by two different sperm cells or a single zygote splits into two, resulting in fraternal (dizygotic) or identical (monozygotic) twins respectively. In the case of identical twins, babies share 100 percent of their genes, whereas in the case of fraternal twins, only 50 percent of the genes are shared, half of which are from the mother and half from the father. 

Heteropaternal Superfecundation twins are fraternal twins who come from different fathers. How this happens is really interesting. The phenomenon can only take place when there is hyperovulation. This means that the ovaries of a female release 2 eggs in a cycle. It is pertinent to understand that both of these eggs can come from the same ovary or one from each ovary. Another important factor that is crucial for Heteropaternal Superfecundation to take place is sexual intercourse. The woman needs to have intercourse with two different partners within a short period of time. This means that she gets sperm of two different origins, each of which fertilizes one egg. The second fertilization is believed to take place after 3 to 4 days of the 1st one, however, it can even take as long as 14 days. In this case, the twins share just 25 percent of their genes, which solely come from their mother. 

Difference between Normal Pregnancy and Heteropaternal Superfecundation

There are certain factors and changes that differentiate Heteropaternal Superfecundation from a normal pregnancy. These are:

Ovulation

Unlike regular pregnancy, in the case of Heteropaternal Superfecundation, hyperovulation is crucial. This means that it happens only when a woman releases 2 eggs, which may be due to hormonal changes or genetic reasons.

Sperm Lifespan And Fertilization

Normally, the lifespan of a sperm within the female reproductive tract is around 5 days, however, in the case of Heteropaternal Superfecundation, it further extends by a couple of days, making it possible for the second fertilization to take place even after 2 weeks. 

Multiple Follicle Maturation

In order to release one egg, a single ovarian follicle reaches maturity in every cycle. In the case of Heteropaternal Superfecundation, this changes, with multiple follicles reaching maturity. 

Genetic Differences

Higher genetic diversity is seen in the case of Heteropaternal Superfecundation as the babies share only 25 percent of the genes coming from their mother. They get different sets of genes from their respective fathers, ultimately resulting in the development of varied characteristics and features. 

Can Ultrasonography Indicate Heteropaternal Superfecundation?

There are certain noteworthy changes that may be evident during ultrasonography, in the case of Heteropaternal Superfecundation. The earliest of these is that there are multiple gestational sacs in the mother’s uterus, each carrying 1 twin, who have distinct genetic makeup. The twins also have separate placentas. 

The size, as well as the rate at which the fetuses grow may vary, based on their genetic makeup. This becomes more evident in the later stages of the pregnancy. They can show different movements & activity levels, rest in different positions, and respond in different ways. 

Does Heteropaternal Superfecundation Make The Pregnancy Risky?

The course of progress of Heteropaternal Superfecundation pregnancies is somewhat similar to standard multiple pregnancies, however, there may be some challenges that are unique to the former and can make it comparatively risky. 

“Heteropaternal superfecundation in itself is not a direct risk, but it may face challenges seen commonly with twin pregnancies” - Dr. Chetan Tatrari - General Physician (Fortis)

Preterm Birth

The risks of preterm birth, which means delivering the baby early, are higher in the case of Heteropaternal Superfecundation pregnancies, which is possibly due to the difference in their growth rates and development. 

Growth Restrictions 

Heteropaternal Superfecundation pregnancies present higher risks of IUGR or intrauterine growth restrictions. This means that one of the fetuses, or both of them, do not develop as they should and their growth is slower.

Abnormalities in Placenta

Since there are multiple placentas in the case of Heteropaternal Superfecundation pregnancies, Complications related to any of these can drastically impact the growth of the babies. 

Twin-twin Transfusion Syndrome

It refers to an imbalance in the flow of blood to the fetuses, which can often give rise to serious complications. 

Delivery Complications

When it comes to delivery and labor, these are more complex in the case of Heteropaternal Superfecundation pregnancies owing to the difference in position, size, and other factors.

Heteropaternal Superfecundation is a rare yet interesting phenomenon. It differs from standard pregnancies in several ways and presents with a different set of challenges.

Did the topic fascinate you? We would love to hear from you. 

FAQs

1. How rare is Heteropaternal Superfecundation?

Heteropaternal Superfecundation is an extremely rare phenomenon. Though difficult to estimate, the incidence is about 2.4% among dizygotic twins.

2. Is it possible to be pregnant by two different guys?    

Yes, it is possible to get pregnant by two different guys at the same time. The phenomenon is known as Heteropaternal Superfecundation and it refers to the fertilization of multiple eggs by sperm cells coming from different males. 

3. How to have twins with different fathers? 

One can have twins with different fathers if they have sexual intercourse with separate males within a short span of time. For this, the woman should have hyperovulation, which refers to releasing more than 1 egg. 

4. How frequent is heteropaternal superfecundation?
Heteropaternal Superfecundation is quite uncommon, accounting for merely 2.4 percent of all dizygotic twins. 

Sources

Twins From Different Fathers: A Heteropaternal Superfecundation Case Report In Colombia 

How to Have Twins with Different Fathers

Superfecundation – from ancient to modern times | Ginekologia i Poloznictwo

A Review On Heteropaternal Superfecundation