A little science behind conceiving twins

Some factors contributing to the increased rate of having multiples is becoming pregnant in the 30s or 40s and/or assisted pregnancy. Particularly the drug Clomid has been linked to an increase in the number of twins and triplets.

In order to be able to conceive non-identical twins naturally, there must be the gene in a woman’s body from her father or mother. The ability to conceive dizygotic twins is a female related issue. On the other hand, having identical twins has nothing to do with the genes!

Internationally, identical twins occur four per 1000. However, the statistics of having fraternal twins varies with race. Africans have the highest rate of dizygotic twins, with Europeans in the middle and the lowest rate of fraternal twins happening in Asia.

There are basically two types of conception that can happen with twins. (some believe there is a third type of twins, read more ..)

1) A single egg is fertilized by a single sperm and between 3 to 15 days after conception it splits and the result is identical or monozygotic twins. If the split happens by day 5, the twins will have two amniotic sacs, two chorions, even two placentas. If the split happens between day 5 and 9, then the twins will have one chorion, one placenta and two amniotic sacs. If the split happens 9 days after conception, then the twins will share one chorion, one placenta and amniotic sac. If division happens later on, then conjoined twins are formed.

Identical twins normally share one placenta, but each can have their own amniotic sac. However, a small percentage of identical twins have two placentas. In that case you may be under the impression that you will have dizygotic twins and get a surprise after birth.

The Placenta’s function is to deliver nutrients to the babies. There can be complications for babies who share a placenta. Of course identical twins are the same gender and share the same DNA. However they will have their own unique fingerprints!

2) Two eggs are fertilized by two sperms and the result is fraternal, non-identical or dizygotic twins. Fraternal twins usually do not share placentas. Each have their own placenta and amniotic sac. They are basically womb neighbours. Having said that, in some cases, the two placentas can fuse together and give the impression of being one placenta. In all reality, you can only be sure what type of twins you are having after you give birth.

Just for you to know Mary-Kate and Ashley Olsen are actually fraternal twins?!!

If you have not heard about the black and white twins you should watch this movie.

Note: Some fraternal twins look almost identical. Twin Zygosity Test is a popular way to find out if your babies are in fact identical. The test is very easy to use. You can prepay you order, receive your DNA testing kit, send back the DNA and receive the result within a short period of time.




  1. hi
    i had fraternal twins in my second birth unlikely one died at two months it was a sudden infant death,can i be able to get twins again?

  2. I had fraternal twins 7 months ago. When they were born the placentas had fused together as one. The thing that we don’t understand is why the membrane separted so that they could move around inside the one placenta. They both have the same blood type and look almost identical. She looks like a girl (petite) and he looks line a boy (massculent). Both we’re exactly the same length/height but their body portions were different. During the pregnancy she was always a little behind him in growth but she would always catch up to him. Everything they do is as if they’re identical but they still have differences. Even now their personalities are differnt but theyre teething the same. How would we name their situation in medical terms?

    • Some twins have the same egg but different sperm. The unfertilized egg splits then two separate sperm fertilize each egg.

  3. I am one of the rare cases – one placenta, two amniotic sacks – one boy & one girl! Born 34wks 4lbs 9 and 5lbs 11!! 

    • I as well have fraternal twins. Boy/girl 2 separate sacs, 1 placenta.My daughter weighed 4lbs 12 oz and my son was 5lbs 4oz. My son is dark hair Brown eyes dark skin. My daughter has blonde hair blue eyes and white skin. My Dr was very surprised to see only one placenta cause they were conceived naturally.doctors say that a very high rate of fraternal twins that shares one placenta are from ivf .

  4. I had 2 sacs 1 placenta & twins boys, born at 34weeks..weighing  5lb 10oz & 5lb 11oz the natural way. They look identical. They both have the same blood type 0-, my family mix them up all the time. The dr. actually told me after giving birth “if by 6 months, they still look the same, their identical”. So I’m thinking about having the DNA test done to know for sure.

  5. hi i really don’t know if i do have twins i never had a sonar checked so i am really worried and my belly is so big and i am having this wight on my two sides of the belly and different kicks and it fells so weird.am i going to have twins or what coz this is my fourth pregnancy witch is really weird plz help

  6. Mom Of Twins says:

    I had 2 sacs at the begining now at week 21 they told me my sac dividing membrane has deminished!! 3 ultrasounds, 2 saw a small layer, one saw nothing!! Similarly, earlier Fraternal Ultrasound specialist told me i had 1 placenta now 1 say i had 2!! My doc checked again and said its 1!! We are totalling confused as of today my week 22 begins and still i havent bought a single thing for my twins!! 

    1 doc said my first twin maybe a girl but second one wasn’t showing doing to the position!! Due to these different results, dont know how to start preparations!! 

    Any ideas? Has someone face similar contradictory results??

  7. Sabastian Larson says:

    My wife was pregnant with a baby girl and was getting normal ultrasounds done and seeing the doctor regularly. We just had our twins yesterday and they were born in the same sac with two different placentas. God Bless Everyone.

  8. I had twins 8 years ago. They were in seperate sacs with their own placentas so I was told they were fraternal. They look alike and as the years go on I can see how similar they are in everything they do so I did the Zygosity test and they are actually identical. 

  9. Hello everyone,I’am 5 months pregnant with two placentas,they say I would have to get a blood test to determine if it’s identical!!!Im just bless to be having twins!!!My husband is so excited!!!Were having twin girls!!!

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