All Twins are Not Equal

Twins are a serious concern.  There is a general lack of information and knowledge about them.  They are not good or exciting.  The only twins that I imagine to be good are those that are at least five years old, healthy and attending school.  Finally a break for the parents.  Twins are a lot of work.  Unfortunately, it has become more frequent to see twins, and there are being posted all over the internet.  It is concerning about the lack of understanding about the serious and life threatening risks that twins face.  They are lucky (in some cases) just to make it through pregnancy and survive.

Take for example a recent picture posted on Facebook.  I won’t show it here, but this is a link to it (I hate to admit that I visited this page, but it is a good place for a laugh or just to let of steam yelling at the screen).  The argument is this:  twin A is pale because of early cord clamping and twin B is darker because of delayed cord clamping.  I call it a bunch of people talking about something about which they have very little knowledge or information.  In the discussion, they clearly mention that this was a “mono” pregnancy, but then seem confused what this means.  If you don’t know the different types of twins, for bloody sakes, DON’T GIVE OUT MEDICAL INFORMATION about TWINS!!

Here is my twin primer.

Zygosity – refers to the number of eggs involved in the conception

Monozygotic – one egg fertilized, and then split into twins.  These are “identical twins“.  They are the same sex.

Dizygotic – two egg fertilized, two fetuses develop.  These are “fraternal twins“.  They can be the same or different sexes.

Simple so far?  Most twins are dizygotic, and this is especially so if the pregnancy results from infertility drugs.  In Canada, about 2/3 of twins are dizygotic.

Chorionicity – refers to the number of chorion (for easy remembering, this is the outer sac and placenta).

Dichorionic – Two chorions.  All dizygotic pregnancies (two fertilized eggs) results in dichorionic pregnancies.  Because there are two placentas and two outer sacs, there must also be two inner sacs (amniotic sac) so these pregnancies are also diamniotic.  Now where this starts to get complicated is sometimes the two embryos implant very close to each other.  Their placentas may touch or even be called fused.  This just refers to what can be seen on ultrasound; the placentas are not actually fused, there is no shared placenta or blood volume, and when delivered, it is not difficult to separate the two placentas.  Identical twins, if the sepearation of the one egg occurs before three days, two distinct embryos will develop, each with their own placenta.  Although they are identical, they do not share a placenta or blood.


Monochorionic – These MUST be identical twins, but not all identical twins are monochorionic.  These are twins that separated from a single egg between days 3-8 after conception.  They represent 2/3 of identical twins.  The separation occurs after the cells that are destined to be the placenta have developed separately from the embyro(s).  This means they share a placenta.  If they share a placenta, they share the blood vessels associated with the placenta, and therefore are likely to share their blood volumes.  These are more complicated twins and anyone who says otherwise has absolutely no clue what they are talking about.  Think about this way, these twins are conjoined at the placenta!!  These twins have only one external sac, and are further classified as to the number of internal sacs (amnions).

Monochorionic-Diamniotic – These twins share a placenta, but each have their own internal sac.  There are essential only two thin membranes between the twins (the amnion for each twin).  They are joined at the placenta, and almost universally share their blood volumes.  However, babies are not known for their sharing skills!  Due to the organization of blood vessels in the shared placenta, it is possible to have an unequal distribution of fluid (blood) and/or nutrients.  Twin-Twin transfusion syndrome (TTTS) is a condition whereby one twin (the donor) is slowly and consistently given its blood volume to the other twin (the recipient).  This occurs in 15% of mono-di twins.  If they don’t share equal portions of the placenta, they will not receive equal nutrition from the mother.  This can lead to one of the babies becoming severely growth restricted.  This also occurs in 15% of mono-di pregnancies.  Even more complicated is when both situations occur at the same time, generally not a good outcome for one or both twins.  These conditions can only be reliably identified with ultrasound and routine screening for these pregnancies will improve outcomes (there are some treatment options).  I promise a future post just about TTTS, I owe it to a friend who lost a baby to this condition.

Monochorionic-monoamniotic – These twins not only share a placenta but share a sac.  These twins separate later, but days 8-12.  These are much more rare, accounting for 1% of monozygotic twins.  This is a very dangerous situation, because they are at risk for all of the other complications with a shared placenta, plus they can tangle their cords and make knots.  This is risky because it can cause one or both twins to die.  The most risky time for these twins is labour.  They are all delivered by elective c-section at 32-34 weeks.

There are other more rare conditions, which as a perinatologist, find very interesting.  However, I would be happy if health care providers and the so-call child birth educators could just get these basics right.  Twins aren’t good, shared placentas are worse.

Back to the picture in discussion.  Do I really think this difference is cause by delayed cord clamping of only one baby??  Absolutely not.  This is a pathological image where one baby is clearly anemic (low red blood cells) and the other is polycythemic (too many red blood cells).  This did not happen at delivery, these babies would have looked exactly the same if delivered by c-section and both cords clamped at the same time.  Reading the site where the picture was posted, they even comment on the fact that the darker twin needed more help.  This isn’t surprising to someone who routinely cares for complicated twins.  Generally, the smaller anemic twin is more fiesty than the bigger polycythemic twin.  The little twin has been fighting to get its fair share, perhaps a little stressed and ready to get out of there.  The bigger twin just got everything given to it, had a cushy environment and is generally not ready to be delivered.  Sudden it has to work to survive – this is why they often need help.  Plus they have extra red blood cells to break down, so they are also at risk for jaundice.

If only twin B had delivered first and had early cord clamping and then twin A second with delayed clamping.  That would have fixed everything, right??  If we are suppose to trust birth, why didn’t these babies just come out in the right order?


16 thoughts on “All Twins are Not Equal

  1. Thank you for your excellent information, it’s good to have more resources to refer people to (rather than having to reexplain over and over!! ) While I do see the benefits of delayed cord clamping (and other healthier procedures in birth) it frustrates me to see photos mislabeled to make a person’s point. I am a CPM, and I take midwifery and correct knowledge very seriously. I’m also very thankful for OB’s trained to care for the women that have need of a more medicalized type of care than can be safely provided by midwives.

  2. This was Not Twin Anemia Polycythemia Sequence TAPS. Other photos in the article clearly show a Symmetrically Vascularized placenta, making this form of TTTS that involves only red cells & not whole blood extremely unlikely. We know the different types of twins. Clearly. We don’t recommend DCC in MoDi due to the fact that overall fluid balance may be maintained by a combination of anastomses that are Asymmetrically crossing the placental equator: ie 5 smaller vessels equal in flow to one large one. These vessels will close off at a rate propotional to their diameter: smaller closing first, larger closing later. Classical DCC waits until the umbilici cease pulsation. This practice can result in an unequal distribution of blood volume between the twins should a situation such as the aforementioned one arise. Immediate clamping of each cord as soon as possible following Delivery is recommended.

    1. I don’t think that I recommended cord clamping. I definitely don’t recommend prolonged delayed cord clamping – the pulsations are arterial, taking blood from the baby to placenta. I generally wait one to two minutes (singletons) or clamp earlier if the placenta is delivering or the vein is collapsing. In mono-di twins, I do quick cord clamping at vaginal delivery. There is a fine balance at c-section, particularly if the the twins are early. There is evidence to support delayed cord clamping of 45-60 seconds in premature infants for benefits. But I take into consideration the entire picture. If the twins are equal sized, equal fluid and major concerns other than preterm delivery, I will delay clamping A until I have delivered B (general at c-section this is under a minute). I therefore have not greatly changed the circulatory patterns because both babies are delivered, so any vascular mismatch is not acutely changed – both twins have ruptured membranes, the uterus is contracting equal on both placentas. However, at vaginal delivery, the delay between twins is longer, so I don’t like to delay cord clamping because it is unpredictable what the circulatory effects are with one twin out and the other other still with intact membranes. However, if the “recipient” twin is delivered first, clamping the cord does not fully correct the problem, because this only removed the baby from the the circulation, the “donor” twin may still be partially perfusing the other placenta. The vein-vein connections may be not protective here. It is all very complicated and no two mono-di sets are the same, because the placental morphology will be different.
      The original reason I posted this picture because of the way the picture was being portray in some circles of conversation – like it proved the “benefits” of delayed cord clamping. I suspect this image does not support delayed clamping in any way. For term babies, the benefits of DCC are minimal at best, and for some pregnancies potentially neutral or even harmful. I do not take a cook book approach to any specific delivery technique, but rather evaluate each pregnancy individually.

  3. I guess debate is not tolerated here. OK. Come to my group on Facebook & Extol the Risk Free Virtue of DCC in MoDi there. Also please note the shade of all the MoDi Pairs who did Classical DCC in the photos. Guess they all had TAPS, right? MoDi gestational & delivery safety are not Curiosities. There is a Clear Threat of Iatrogenic Acute TTTS in the performance of classical Delayed Cord Clamping in MoDi Pairs. Your removal of this posting will not change that. Do your studies, Doctor. Reject Dogma.

    1. There is no opposition to debate here. My filter is set so that I have to approve comments before they are posted – given that it was a long weekend and I was catching up on sleep after two twenty-four hour shifts in three days – I am just reviewing the comments now. I don’t get a lot of comments and I like to, whenever possible comment back, because I appreciate the discussion.

    2. I am not sure what your point is – do you support DDC or advise against it? I take a middle road and evaluate the overall pregnancy – they are some cases that may benefit, and some cases in which it may be harmful. I don’t recommend patients turn to Facebook to determine which it the best option in their particular case. I am not sure what you want me to read up on, I have a fairly good understanding of TTTS and other complications of Mon-di twins. I spend a fair amount of my clinical work caring for these twins, and also advocating for better care at all levels of access to the system. TTTS is not the only problem that affects this twins, it is just one of the problems that can be encountered, and I try to evaluate each on a case to case basis.

  4. Excellent discussion!
    I would be extremely grateful if you would consider joining my group on Facebook for discussion. I brought proper monitoring advocacy of Modi Twins to the group with help from multiple sources including some doctors.
    Your description above of DCC in MoDi is very helpful. We have been looking for research in regards to this.
    Thank you,

  5. Excellent discussion!
    I would be extremely grateful if you would consider joining my group on *gasp* Facebook for discussion. (I saw that you mentioned not getting information from a site such as that and I can understand why in most cases) I brought proper monitoring advocacy of Modi Twins to the group with help from multiple sources including some doctors and researchers.
    Your description above of DCC in MoDi is very helpful. We have been looking for research in regards to this.
    Again, I would love for you to at least come take a look around my group. There’s over 2500 members soaking up our information and strongly supporting it.
    Here’s a link to the group. I hope links are allowed so you can see it. If not, the name of the group is simply MoDi Twins.
    Thank you,

    1. I would like to clarify I am not against patients using the internet. I am concerned when they take medical advise from strangers on the internet as the “truth” over what their own physicians are saying/recommending. I actually think the supportive side is very helpful, and I do recommend my patients with complicated pregnancy reach out for support. I have referred many women with Mono-Di twins complicated with TTTS to the TTTS Facebook site. The emotion and practical support in invaluable. It is the fringe medical advice that makes me more concerned.

  6. Hey there, sorry to unbury your old post, and that my comment is only vaguely related to the conversation, but when you’re a mom looking for answers you ask where you can…

    I am carrying spontaneous triplets (yikes) and they are tri/tri (thank goodness).
    I am considering delayed cord clamping since they will most likey be premature (making term would be amazing but statistically unlikely of course) and it could help them. There is no risk of TTTS! But I am finding most people suggest waiting until the cord stops pulsating and here you indicate that this might be bad? That the blood is actually being pumped -to- the placenta at that point? I have seen it said by many sources, some seeming quite reasonable, that waiting until pulsating stops is good, and the only increased risk is jaundice.
    So looking into the other opinions out there, planning to make an informed decision.


    1. Congrat on the triplets, I hope you have an uneventful pregnancy and three healthy babies.
      Delayed cord clamping is beneficial in preterm babies. However, it is the venous flow that is returning from the placenta. Arterial flow causes the pulsations and is heading towards the placenta. I generally watch the cord and when the vein collapses clamp the cord. For triplets, I suspect you will be offered a c-section. This complicates but does not prohibit delayed cord clamping. In your case there will be four patients – you and the babies. The interesting thing that is not studied well is the amount of blood transferred in multiples. Most of the benefit of delayed cord clamping is allowing for the first big breath, reducing vascular resistance in the lungs to replace the low resistance of the placenta. This allows a more gentle vascular transition for the babies (likely relating to the decreased risk of IVH in preterm infants). Most of the blood transfer in delayed cord clamping is from the squeeze of the placenta by the uterus. What isn’t clear is how much squeeze the placenta for baby A will get if B&C have yet to be delivered. This means without the squeeze of the uterus, the placenta can still receive blood from the arteries and will not be forced to return venous blood at a faster rate. Therefore it is theoretically possible that the first triplet wont get the extra blood volume. We also have to watch your blood loss. It takes time to delivery triplets and the uterus will be cut open. This will result in bleeding for you. The longer the cords are delayed, the more blood you will lose. It is a trade off and nothing is simple. I would recommend you talk to your care provider and make a plan together. Non-medical web sites tend to simplify the issues, trust your doctor has your’s and your babies’ best interest in mind when making plans for delivery.

      Good luck!!

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