Medical experts say that it is possible for twins conceived naturally to have two different biological fathers.
The phenomenon, they say, is known as heteropaternalsuperfecundation — a phenomenon that occurs when two different males father fraternal twins.
They experts say that in general, superfecundationis rare among humans but it is common in animals.
The phenomenon is also referred to as double paternity, even experts warn that the incidence may be substantially higher in small selected groups of dizygotic twin maternities, such as those of women engaged in prostitution.
Researchers describe superfecundation as the fertilisation of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two different fathers.
According to experts at the European commercial social networking site for scientists and researchers, ResearchGate, superfecundation is an extremely rare phenomenon.
“It occurs when the second ovum (released in the same menstrual cycle) is fertilised by sperm cells from separate sexual intercourse.
“Superfecundation can occur only when a woman has had sexual acts within a short period of time from one another,” the experts assert.
Again, experts at online platform, The Conversation, state that, for heteropaternal superfecundation to occur, the mother’s body must release two eggs during ovulation that are then fertilised by two sperm cells from two different men.
Speaking in an interview, Consultant Obstetrician and Gynecologist, Dr. Oluseyi Adelekan, said superfecundation occurs when a woman releases more than one egg during a cycle, such that if the woman has sex with two different men within the cycle, she can get pregnant for each of them.
“So let’s say, she releases an egg today and another 24-72 hours later, and she has sex on those different occasions and the eggs get fertilised by different sperms,” he said.
Explaining further, Adelekan said, “Some women can ovulate more than once within a cycle, at intervals of few hours to few days.
“And these eggs released at different times can be fertilised by different acts of sexual intercourse, either by the same man or a different man.”
Adelekan, who is also a fertility expert, said though the condition is rare in humans, it has occurred in few instances.
“There was a white woman who had sex with her husband and was raped a few days apart by a black man. She got pregnant and delivered twins — one white and the other black,” he said.
Continuing, Adelekan noted, “It is common in animals and it has been found to occur a few times in women. It has occurred following an IVF.
“After transplanting the embryos into the womb, the woman also ovulated and got pregnant from the sex she had around that time.
“It is rare because nature has made it in such a way that once you get pregnant, you don’t get to ovulate again. However, on a few occasions, ovulation has occurred.
“I cannot say I have experienced any, because the only way to know is by doing Deoxyribonucleic Acid [DNA] testing to be able to know if the babies are from the same father; or we can do some other genetic testing to know if they occur at the same time or at different times,” he said.
Also, a Consultant Obstetrician & Gynaecologist at the George’s Memorial Medical Centre, Lagos, Dr. Faye Iketubosin, said superfecundation is an extremely rare occurrence in humans.
“The only way it can happen is if a woman has two different partners around the time she is going to ovulate and in that particular cycle, she releases two eggs, then it’s possible.
“It occurs when a woman has two partners and one can do a DNA test to find that the twins do not belong to the same father,” he noted.
A senior Obstetrician and Gynaecologist at the Federal Medical Centre, Ebute-Metta, Dr. James Taiwo Odofin,added that superfecundation is a term used to describe when there is fertilisation of two ova — when two ova are being fertilised in the same menstrual cycle by different sperm.
“It’s not common and the ones we see in medical literature or the ones that are celebrated is very obvious.
“In such cases, you’ll see that one of the twins is white and the other is black; or one of the twins has a blood group that is totally different from that of the mother or the father.
“We also have fraternity twins (non-identical twins). Some of the twins that don’t look alike might even be products of heteropaternalsuperfecundation.
“It might be that the same man at a different point in time fertilised two different ova and it’s still different genetic makeup,” he said.
Odofin noted that superfecundation is common in mammals and it’s better explained in them.
“For example, the domestic hen ovulates for like 10 days; so, at a different point in time, they can be impregnated,” he said.
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