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Q&A: How do twins develop?

It’s twins! How did they develop?

Re: It’s twins! How did they develop?

The Bump Expert

If you’re pregnant with twins, you’ve probably spent more than a few minutes wondering how planning for one baby suddenly turned into planning for two. Well, whether it’s a result of your age, genetics, or fertility treatments, having twins is something of a miracle (in fact, they make up a mere 3 percent of all pregnancies). Even if you plan to dress your babies in matching onesies (a sure way to elicit an “awwww!” from strangers), their similarities in appearance depend heavily on their development.
Identical twins develop after your fertilized egg splits in half and creates two genetically identical (aka monozygotic) embryos. If this happens a couple of weeks after conception, then each baby gets his or her own gestational sac and placenta. If they split up later, the two embryos will probably share the same sac (consider it a prebirth lesson in sharing!).
Fraternal twins (or nonidentical twins) develop when two separate sperm fertilize two separate eggs. This creates two genetically different (dizygotic) embryos. In this case, the only thing the babies will be sharing (for now) is your uterus (give them some credit -- it’s not that big!).

American College of Obstetrics and Gynecologists. Your pregnancy and birth. 4th ed. Washington, DC: ACOG; 2005.


By Sandra Le Plasse

Q&A: How do twins develop?

Also, fraternal twins are generally from the maternal (mother's side) and it is because there are 2 eggs to fertilize instead of the normal one with ovaries alternating ovulation. I have fraternal on both sides of my family so I was glad to know my chance wasn't increased from my dad's sister having twins but only my mom's mother being a twin.

amyg1120 |

Q&A: How do twins develop?

There are two ways it can happen. Identical twins are created when the egg splits shortly after fertilization or fraternal twins who come about when the women releases two eggs that are both fertilized

EmShea |

Q&A: How do twins develop?

My twins are identical and they developed about 6 days apart and they share the same placenta but different amniotic sacs. I guess I am different from the norm.

NewX2 |