U.S. doctors online nowAsk doctors free
A 40-year-old member asked:

Heterochromia in one identical twin, not the other. are they fraternal?

1 doctor answer2 doctors weighed in
Dr. Nikolaos Zacharias
Maternal-Fetal Medicine 27 years experience
Not necessarily.: Identical vs. Fraternal twins are archaic terms that no longer apply to the modern perinatal terminology., however are still generally true and understandable to lay people. The color of eyes is not the determining factor in zygocity or chorionicity of twins - check prenatal records and placental pathology!

90,000 U.S. doctors in 147 specialties are here to answer your questions or offer you advice, prescriptions, and more. Get help now:

Ask doctors free
Educational text
Talk to a doctor
24/7 visits - just $39!
50% off with $15/month membership

Similar questions

A 45-year-old member asked:

How do I know if I am having identical or fraternal twins?

2 doctor answers9 doctors weighed in
Dr. Padmavati Garvey
A Verified Doctoranswered
31 years experience
Depends: You can determine it based on ultrasound if there is only one placenta. However, often times you need to have babies tested after they are born. Even twins that "look" identical may not actually be identical.
Dr. Michael P Vaughn
Allergy and Immunology 35 years experience
Some times blood typing is done for twins in the hospital, if the twins have different blood types then they would not be identical, conversely, the same blood type would not prove identity.
Oct 31, 2011
Dr. Patrick Weix
Specializes in Obstetrics and Gynecology
If the twins share a sac inside the uterus, such as monochorionic /diamniotic or monochorionic/monoamniotic, then they are identical.
Oct 31, 2011
A 35-year-old member asked:

Are fraternal or identical twins more common?

2 doctor answers2 doctors weighed in
Dr. Sheila Goodman
Specializes in Obstetrics and Gynecology
Yes: Fraternal twins are 3 times as frequent as identical. Fraternal twins happen when there is double ovulation and 2 eggs get fertilized. They are the type of twins that run in families. Identical twins come from 1 fertilized egg which separate in early gestation. Depending on when they separate, the babies can be in 2 distinct sac (di/di), 2 sacs within a shared sac (mono/di) or 1 sac (mono/mono).

Related questions

A 47-year-old member asked:
1 doctor answer3 doctors weighed in
A 45-year-old member asked:
1 doctor answer1 doctor weighed in
A 36-year-old member asked:
1 doctor answer1 doctor weighed in
A female asked:
1 doctor answer1 doctor weighed in
A 43-year-old member asked:
1 doctor answer1 doctor weighed in
Last updated Sep 15, 2017
Connect with a U.S. board-certified doctor by text or video anytime, anywhere.
24/7 visits - just $39!
50% off with $15/month membership


Content on HealthTap (including answers) should not be used for medical advice, diagnosis, or treatment, and interactions on HealthTap do not create a doctor-patient relationship. Never disregard or delay professional medical advice in person because of anything on HealthTap. Call your doctor or 911 if you think you may have a medical emergency.