The Hetero-paternal Superfecundation : Twins From Different Fathers ?

(image source)

Hello, Fellow steemians! I Hope everyone is doing well. Its nearly been a month since my last post, today I will be discussing an interesting science topic which I'm pretty sure you had not heard of before!

What is Heteropaternal Superfecundation?

Superfecundation is a rare condition where two ova are released during a single menstrual period and both get fertilized by different acts of coitus at a short interval of time, usually few days.
Whereas we use the term Heteropaternal superfecundation when the two acts of coitus are by different person i.e. two ova are fertilized by sperms from two different males.
Here is a case example of this:

"Oliver and Emma are a couple married for about a decade. After a few years of marriage, they gave birth to twin male babies. At first, parents did not notice any difference in them. But as the time passed, despite being twins they looked completely different. One was fair skinned and the other was dark-skinned(just like the picture above) and they were different in builts. The husband had some suspicion of interchange of one baby in the hospital during delivery so he did DNA testing of them. What they found out was surprising- These twins had completely different DNA make up which was not possible from a single father but both of them matched with the DNA of mother. Later on, the wife revealed that she had coitus with another man few days before she had with her husband. then DNA of the suspected child was Matched with that man and it was proved he was the real father of one of the twins"

Have you ever heard a story like that? I guess not. From this case story, you must have made an image of this condition in your mind.
This was a brief intro to the condition. Now we will talk about the mechanism behind this.First of all, we will discuss the normal mechanism of ovulation and fertilization and then we will see what different thing happens in Superfecundation.

Normal Ovulation and Fertilization

Ovulation is the process of release of mature ova from graffian follicle of the ovary in each menstrual cycle. Its a complex neuroendocrine process involving Hypothalamo-pituitary-ovarian axis, .i.e series of information pass from the hypothalamus to pituitary and then to ovaries in the form of various hormones.

During the entire reproductive life, a female can ovulate about 400 ova, one in each period. These ova are nothing but the matured germ cells of the ovary. At birth, there are about 7 million germ cells which reduce to 2 million by birth. As a girl reaches the puberty, about 400,000 of oocyte remain in the ovary. And only 400 out of those 400,000 are ovulated in the entire life.

Fig.- Normal menstrual cycle showing relation of change in hormone level(FSH & LH)) with the uterine and ovarian changes(you can ignore other things)(image source)

The process of maturation of an ova begins in the early days of the menstrual period. FSH(follicular stimulating hormone) released from the pituitary in response to low estrogen during menstrual bleeding starts to stimulate the follicles of the ovary. Few thousands of primordial follicles are recruited and they undergo maturation. Out of those, only 20 follicles (10 from each ovary) reach the matured state(antral follicles). And again, out of those 20 antral follicles, only one follicle grows enough to become a dominant follicle whereas other follicles die. In the end, only one egg/ovum is released in each menstruation(i.e only the dominant follicle will release the ovum).
You must be thinking- _" what's the basis of one follicle being a dominant follicle?"_ The answer is very simple, the follicle containing the highest concentration of estrogen and the maximum number of FSH receptors will get proper stimulus from the pituitary(Through FSH) and thus gets proper nutritional support for maturation of ova inside it. The follicular stimulating hormone induces LH receptors on the dominant follicles. later on, at about 14th day of cycle, LH(luteinizing hormone ) surge occurs(LH surge - the anterior pituitary releases very high amount of LH) and results in ovulation.

Fertilization

Fig. shows a schematic diagram of fertilization, ova is taken up into the fallopian tube and sperm from cervix travels to fallopian tube where fertilization takes place(image source)
The ova , after the ovulation is taken up by the fallopian tube. Whereas the sperm after coitus travels in the female genital tract i.e. from vagina -> cervix-> uterus-> Fallopain tube. ova and sperm meet at ampulla of fallopian tube and fertilization takes place. Ova can survie just 24 hrs after ovulation but sperm can survive upto 4-5 days inside the female tract. So,fertilizaion can occur by a coitus occuring 2-3 days before to one day after ovualtion.

Now, let's talk about the proces of Twinning : How twin Babies are born?

(image source)

Twins can either be monozygotic or dizygotic. When one sperm fertilizes single ovum a single zygote is formed. If that zygote later on splits into two parts, it will form two fetuses and this is monozygotic twinning. Whereas there can be another condition where two sperms fertilize the two ova into two zygotes & thereby form twins, this process is dizygotic twinning. Earlier I have said about the dominant follicle where only one ovum gets ovulated in one cycle, you need to note that sometimes two ova are released in single cycle, It can occur once in 100 cycles. So the "Domiant follicle" theory does not apply here.

What happens In the hetero-paternal superfecundation?

Up to now we have learned about Ovulation, fertilization and the mechanism behind twinning. The process of superfecundation is not much different from twinning .
In dizygotic twinning, as we have discussed above one coitus can produce two zygote and then twins. In superfecundation, two acts of coitus are required but at short interval of time where the sperms can fertilize two ova released at different points of same menstrual cycle.
Now, in Hetero-paternal suprfecundation the coitus should be with different males. Following conditions are required for it.

You have to ovulate twice (dizyogtic). This is actually not so rare an probably happens in more than 1 in 50-100 ovulations.
You have to have sexual intercourse with different men within a couple of days to one week prior to ovulation. That allows two different sperms(from different male) to fertilize two separate eggs.(source)

Here are some true case stories of Heteropaternal superfecundation if you like to read:

1. Case of Justin and Jordan, dallas
2. Case of jayla and julius
3. Case of heteropaternal suprfecundation,vietnam

Superfetation is not same as superfecundation !

There is another term called "superfetation" which comes along with superfecundation and some people might consider it as the same thing, but it is different in the fact that It occurs in two different menstrual periods. when two ova released in different menstrual period get fertilized, we call it as superfetation. A female gets pregnant who is already in her pregnancy. This is very very rare and is only reported in animals.Generally, the 2nd fetus is small and premature when both are delivered at the same time. But there can be the birth of 2nd fetus after some time of birth of 1st one where the 2nd child is also fully developed.

That's all for today, we have learned something new about ovulation, fertilization, twinning and superfecundation. If you have anything to ask regarding this post feel free to leave a comment.UPvote and resteem this post if you liked it and follow @himal if you do not want to miss my future posts.
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References
1.http://americanpregnancy.org/getting-pregnant/understanding-ovulation/
2.https://en.wikipedia.org/wiki/Ovulation#cite_note-Marieb-8
3.Essentials of forensic medicine and Toxicology, K.S.N. Reddy,33rd edition
4.DC Dutta's textbook of Gynaecologly, 7th edition
5.https://academic.oup.com/humupd/article/14/1/37/827500

Images
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