Karan Johar’s ‘Bad Newz’ seems like a comedy film from the trailer, but it has touched upon a rare medical condition called heteropaternal superfecundation where two eggs get fertilized by sperm from different men.
The term ‘heteropaternal’ means different fathers and ‘superfecundation’ is the fertilization of multiple ova during the same cycle. Genetically, these two twins are half-siblings, sharing the same mother but different fathers.
According to a paper in Animal Genetics, the phenomenon is common among sheep, rams and cows as females have mating with multiple males and this increases the chance of them producing different offspring. The condition is quite rare in humans, with only few cases reported worldwide.
What Happens During Superfecundation in Humans?
There are two different occurrences for superfecundation to take place: a woman can release two eggs at the same time since the sperm can survive for a few days in a female reproductive tract in the womb and fallopian tube. It would be possible that the woman could have intercourse with a man in advance of the eggs being released, and another just after ovulation.
In another situation, the woman releases two eggs a few days apart but in the same reproductive cycle.
According to data in 2021, around 3% of total live births were multiple births, majority of which were twins; fraternal twins make up for 70% of twin births. With the increase in the In-vitro fertility (IVF) treatment, the cases of twin births have increase over the past few years.
Statistics show one in 400 pairs of fraternal twins could be born through heteropaternal superfecundation. In 2020, only 19 cases of heteropaternal superfecundation was reported.
What are the Risks Involved?
Pregnancy out of heteropaternal superfecundation could increase chances of developing type 2 diabetes, hypertension or even pre-term birth in some cases. In certain cases, babies can have low birth weight.
Mother also require close monitoring otherwise incidence of Caesarian section deliveries might increase.
Experts also say children born out of heteropaternal superfecundation might differ in height, and develop genetic issues passed on by their respective fathers.
Identical twins share 100% of their genes, classic fraternals share around 50%, and fraternal twins from different fathers have an average of 25% of the same genes (just like half siblings).
It’s also important to note that two sperm can’t fertilise the same egg. Double fertilization means there would be too much DNA in the cell, hence it would not be viable. There is also the case of “superfetation,” when someone with child becomes pregnant again during separate cycles. But this is also very unlikely in humans because the pregnant body creates an environment that suppresses ovulation, according to a report by McGill University.
Cases of Heteropaternal Superfecundation
In 2022, a 19-year-old woman in Brazil gave birth to twins who actually have two different biological fathers. According to a Daily Mail report, the mother had doubts about the father of her children for which she took the paternity test.
After the test, she found that only one of her kids showed positive for the DNA test while the other one did not. “She then remembered that she had sex with a different man on the same day and when this second person took a test, it showed he was the second twin’s father,” the report said.
In May 2015, a case in New Jersey made news when a court ruled that a father did not have to pay child support for a second twin because DNA evidence showed that he was a father to only one, according to the Star-Ledger, as reported by The Washington Post.
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