Can anyone tell me whether you can tell if twins are fraternal vs. identical based on their placentas? Working in the NICU, an admit's placenta is often sent to pathology. We get the report back, and on twins, it specifies whether the babies were separate placentas, fused placentas, separate chorion/amnion, etc.

The parents usually wonder and I suspect you can tell from the palcentas but I just can't remember from back in OB class...

Usually two sacs are identified with fraternal twinning. Two placentas DO mean you have fraternal twins, but ONE placenta DOES not reliably tell you that the twins ARE identical. They, too, may be fraternal, having shared one placenta. Does that make sense?

so if they have the same sac and same placenta that means they are identical?? I dont understand it either KrVRN

There's MO-MO, MO-DI, and DI-DI. Mono-chorion, mono-amnion, mono-amnion, di-chorion, and di-chorion, di-amnion. If it's di-di, definitely 'fraternal', if it's mo-mo, definitely 'identical', mo-di, I THINK they are identical, because there's only one placenta, one outer membrane and 2 inner membranes. BUT, I'm not sure about that one.

If you ever have a chance to listen to Frank Mannino's lecture, "I hate twins", it might help to understand it.

MO-MO twins have a greater chance of coming to grief because it's too easy to get their cords tangled.

Interuterine Appearance of Twins:

Identical twins can have their own, or share both the outer sac (chorion) and the inner sac (amnion):

1 chorion, 2 amnions, 1 placenta (most common) roughly 65-70%

2 chorions, 2 amnions, fused placentas

2 chorions, 2 amnions, separate placentas (about 25-30%, this includes fused placentas)

1 chorion, 1 amnion, 1 placenta (rare) 1-5% These are termed monoamniotic/monochorionic twins.

If identical twins split early after fertilization, then each twin will have it's own chorion and amnion. If the egg splits somewhere between 4-8 days after, each will have it's own amnion, but share a chorion, about 2/3 of twins are like this. If they split after the 8th day, they will be monochorionic/monoamniotic, and anytime after the 12th day, they will be conjoined. Some researchers believe that monochorionic/amniotic twins were very close to being conjoined.

Fraternal twins always have their own chorions and amnions, as well as placentas, but the placentas may become fused and look like one placenta, so it may not always be possible to tell if your twins are identical or fraternal from the placentas. Fraternal twins can't share a chorion or amnion.

It is difficult to tell if twins are identical or fraternal from an ultrasound unless they are monochorionic/monoamniotic or there is only one chorion clearly visible. One chorion would mean the twins are identical.

The only sure way to know if your twins are identical or fraternal (barring them being of different sexes) is a DNA test. I hope this information helps out! I am a mother of twins that are now 9years old, they had one placenta but seperate amnion and chorion, my OB said they were fraternal based on examination of the placenta. My boys look identical and I can't even tell them apart at times, and neither can their teachers or friends.

Respectfully

Denise

:roll :roll :roll

Thanks everyone. I was asking becasue I had an older, experienced nurse tell me that one placenta meant identical for sure. I was pretty sure she was wrong. I knew that placentas can fuse. She was also telling a set of parents that their twins were identical because they shared a placenta. As I recall, they were one chorion, 2 amnion, one placenta babies... which tells us nothing other than they are in the 65-70% majority.

Does separate placentas always mean fraternal?

I had always thought that it was necessary to examine the placenta(s) and membrane(s) in order to determine the type of twinning. About 10 years ago, we had a hot-shot perinatologist who indicated that it was possible to determine the type of twinning on U/S. She examined a patient carrying twins and determined that the babies were mono-mono with a single placenta and at high risk of twin to twin transfusion. She recommended an elective C/S at 32 weeks to minimize the risk of this happening, but mis-timed the steroid dose given to the mother. Despite U/S which estimated the babies' weights to be similar and within the norms for their gestational age, they were sectioned and suffered severe RDS, leading to long term complications for both. Blood typing done prior to their first transfusions revealed different blood types. They weren't identical after all, and therefore had virtually no risk of twin to twin transfusion. Pathology indicated the babies had separate amnions and chorions. What a shame the doc substituted high tech graphics for common sense care.