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Double is not always trouble

Sharing a special bond... Non-identical twins Tapur and Tupur Chatterjee. Photo: R. Ragu  

Couples receive the news that they are going to have twin babies sometimes with excitement and joy and sometimes with a cautious “We are not sure if that is good. Should we be concerned?” Then, once the news sinks in, one of the first questions that comes up is “Doctor, are they identical twins?”

Why do twins happen?

Twin pregnancies are on the increase nowadays and that is partly because more couples resort to subfertility treatments to conceive. Twins can happen when there are two oocytes or eggs produced in a cycle and both eggs get fertilised by two separate sperms resulting in two different embryos. These babies can be of different sexes and are what are commonly called “ non-identical twins” or in medical terms dichorionic diamniotic (DCDA) twins.

Alternatively, a single egg is fertilised and one embryo is formed, but it splits or cleaves into two when the cells are still not differentiated and two embryos result. This cleaving of a single embryo can happen at different points in time and depending on when the cleaving occurs, different types of twins result. These twins will be “identical” and of the same sex, but they may grow in separate sacs or share a placenta — the monochorionic twin

If the cleavage happens within 4 days, we get two babies with separate placenta, if it happens between 4-8 days, the placenta is shared and if it happens after 12 days, then we have problems like conjoined twins where parts of the body may be fused.

As doctors, we need to know what type of twins we are seeing because of the possible problems that can arise with some kinds of twin pregnancies. Fundamental to the management of a twin pregnancy is to know if the babies have separate placentas or not.

How do we identify what type of twin it is?

The identification of chorionicity or number of placentae is the first and important step in managing a twin pregnancy. It helps us in segregating which type of twins requires closer surveillance. This is best done by a scan at 11-12 weeks when the chorionicity can be diagnosed with accuracy. As the pregnancy progresses, this becomes increasingly difficult.

Why is it important to know if babies share a placenta?

If we have two babies with separate placenta (DCDA twin), then it is like two independent babies growing and usually there are no problems. When the two babies share a single placenta, they are sharing the blood supply. In this case if they don't get an equal share of placental blood supply, problems of growth can occur. While the majority of monochorionic twins will be healthy, there are significant problems that can affect a small percentage of them.

Knowing what type of twin a woman is having helps plan her care better as the approach to monitoring the pregnancy is different in the two kinds.

What are the problems unique to monchorionic twins?

Babies with a single placenta (monochorionic twins) also have blood vessels communicating with each other. Typically, blood from one twin flows into the other twin through these communications, which are deep in the placenta, and are brought back through blood vessels, which are superficial in the placenta. This happens in such a way that the blood-flow to both babies is balanced. In about 15 per cent of the cases, there is an in an imbalance of blood supply. The quantity of blood brought back from one foetus is not equal to the flow into it which causes one foetus to be deprived of blood supply and nutrition and the other receiving more than its usual share. This condition is called “Twin Twin Transfusion Syndrome” (TTTS). In this condition, there can be accumulation of fluid around one twin and lack of fluid around the other. The uterus becomes bigger and there is a risk of preterm delivery.

Another condition, which is unique to monochorionic twins, is called “Twin Reversed Arterial Perfusion sequence” (TRAP), where there is a peculiar pattern of blood-flow between the babies and one of them is often abnormal.

Monochorionic twins, therefore, need more frequent monitoring and bi-weekly follow-up is required. In some cases, weekly monitoring may be required. During the monitoring, we look for the size discrepancy between the twins. A weight difference of more than 15 per cent is considered as significant. We also look to see whether one baby is producing more urine than the other, leading to difference in the levels of fluid around the baby. These are signs of twin-twin transfusion. We can also assess the blood flow to the babies by using colour Doppler.

What can we do if these problems do arise?

The question is, do we have a method of saving these babies?

Fundamental to these problems is the sharing of blood supply and connection between blood vessels. Over the last decade, extensive research has shown that by disrupting the vessel communications between the twins using “foetoscopy” and laser, it is possible to give hope to these couples.

A fetoscope is a small instrument with which we can enter the pregnant uterus and have a direct vision of the foetus and placenta. In foetuses where problems such as those described arise, then foetoscopic laser photo coagulation of the blood vessels can be considered.

In cases where one of the twins is abnormal, and can affect the normal twin, it is now possible to occlude the umbilical cord of the abnormal twin under ultrasound guidance using a special instrument called “bipolar forceps”.

While it is true that most of the times twin pregnancies result in healthy babies, we need to be aware that problems could arise and take care to monitor appropriately to pick them up. In the event of such problems arising, we do have the technique and technology to try and treat them.

What happens when there are more than twins?

More is not merrier especially when we are dealing with more babies in the womb. With the advent of specialised treatments for infertility, there has been a significant increase in the number of higher order multiple pregnancies. It is not uncommon to see triplets, quadruplets, quintuplets (five babies) or even more. The highest number we have seen is octuplets or eight babies!

Almost always as a result of infertility treatment, a significant number of higher order multiple gestation can be prevented by controlled, assisted reproduction techniques. A host of problems can result in these situations. The most important problem when we deal with higher order multiples, especially more than three, is the risk of an extremely preterm delivery and neonatal problems.

Vidya and Ajay had conceived after 10 years by induction of ovulation and intrauterine insemination. Their joy on seeing a positive urine test turned to anxiety when at the first scan their doctor told them they were going to have three babies. They were not sure what to do and how they could handle three babies.

The doctor explained to them that there is a choice of selectively reducing one of the three babies while in the womb at about 11 weeks. They were also told that if they choose to have all three, they could but there was a risk of preterm delivery. While triplet babies can do well even if born preterm, there is a cost of neonatal care that couples must be prepared for. It is a very difficult choice for any couple to make. When a couple makes a choice to have triplets, they have to be prepared for the cost of neonatal care if indeed they have three preterm babies.

However, if there are quadruplets, the risk for preterm labour is about 40 per cent and foetal reduction is an option to be considered to ensure better outcome. Foetal reduction involves injecting a small amount of potassium chloride into the heart of the foetus to stop the heart beat.

While foetal reduction is not a very difficult procedure if done by an expert foetal medicine specialist, it is not without problems. This risk of foetal loss due to the procedure is about 5-10 per cent. There is nothing more anguishing than a couple having conceived with IVF having been told they have five babies, going through a reduction procedure and then having the misfortune of loosing all five babies.

Foetal reduction is an emotionally draining procedure not only for the couple but also for the person performing the procedure. This problem can be minimised when the number of embryos replaced are minimised to two and this is a completely avoidable problem that both ART units and couples undergoing such treatments should focus on.

Dr. S. Suresh is an Adjunct Professor at the MGR Medical University. He founded the Foetal Care Research Foundation, a not for profit charity trust, in 1993. and set up the Birth Defects Registry of India in 2001, now functioning in over 600 hospitals across India.


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Printable version | Jun 18, 2021 2:06:43 PM | https://www.thehindu.com/features/magazine/Double-is-not-always-trouble/article15580346.ece

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