A Single Placenta But 2 Children Sharing: Selective Fetal Growth Restriction

Written by Sophie Groene, PhD-student at the Department of Pediatrics (Willem-Alexander Children’s Hospital (WAKZ)) and the Department of Biomedical Data Sciences at the Leiden University Medical Center (LUMC) in the Netherlands. Her research focuses on monochorionic twins with selective fetal growth restriction, for whom she is dedicated to improving patient care and parent counselling.

What Happens When There Is Unequal Sharing?

Approximately 70% of identical twins are monochorionic, which means that they share a single placenta (mono- = one, -chorionic = placenta). Unfortunately, this shared placenta can give rise to a spectrum of complications in 25% of pregnancies. One of these complications is selective fetal growth restriction, which occurs when the placenta is unequally shared. As a result, the twin with the smaller placenta share becomes growth restricted, whereas the co-twin with the normal placental share grows normally. This unequal sharing causes a growth difference between the twins during pregnancy, and sometimes, one twin can be more than double the size of the other twin.

Researching Selective Fetal Growth Restriction

There are still a lot of questions about the long-term health of twins with such a growth difference. Are the differences we see at birth still present at a later age? And does the difference in growth also have an effect on the development of the brain, the heart or the lungs? To answer these questions, we have started the LEMON study in our center in the Netherlands, focusing on the long-term outcomes of monochorionic twins with selective fetal growth restriction.

In this research, we are inviting all twins with selective fetal growth restriction born in the LUMC between 2002-2017 for follow-up. This follow-up consists of multiple measurements to get a complete overview of the health of these twins. We perform a neurodevelopmental test and a neurological examination (examination of movement) to look at neuropsychological development

Picture. This picture shows a monochorionic placenta injected with colour dye. The placental share of the firstborn child is injected with pink and blue and the share of the second-born child with green and yellow. The firstborn had only 20% of the placenta to draw nutrients and oxygen from while the secondborn had 80%.

We also make an ultrasound of the heart and large blood vessels and do a lung function test, to investigate the structure and functioning of both the heart and lungs. Moreover, we measure growth and use the growth curves from the primary care system to get insight into childhood growth patterns. Lastly, we collect a buccal swab to see whether there are differences in the setting of their DNA that we can relate to the difference in growth that they have experienced in the womb.

We would not be able to perform this research without the efforts of the twins and their parents. Their enthusiasm for participation is noteworthy. Parents share their experiences, the differences between the twins that they perceive, and sometimes even their worries with us. This is extremely valuable, because they know their twins the best. The twins get more information on what makes them special, usually with a picture of their own placenta from the archive. They enjoy two afternoons filled with all kinds of fun tests, from challenging assignments in the neurodevelopmental testing to the chance to get to see their own heart at the ultrasound examination. Afterwards, they often fanatically compare their answers and results (hoping to have performed better than their co-twin).

We want to thank the twins and parents who are participating (and will participate in the future) in the LEMON study. With their help, we have the possibility to get more insight into the long-term health of monochorionic twins with selective fetal growth restriction, in order to further improve care for these special twins.

For more information about the LEMON study and our other research, please visit our website: www.twinlifestudy.info