Striking images of unborn twins have revealed how siblings fight for space in the cramped surroundings of their mother's womb. The images also offer improved medical diagnosis of a potentially life-threatening condition called twin-to-twin transfusion syndrome (TTTS).
The unprecedented look at twins' gestation is afforded through a recently developed form of magnetic resonance imaging (MRI), used by clinicians at London's Center for Fetal Care. Dr Marisa Taylor-Clarke, who also works at the Robert Steiner MR Unit at Imperial College London, recorded the images, says the technique, known as over sampling, affords a unique view of twins' relationship during their mother's pregnancy.
"We haven't really been able to see before in such real-time complete pictures how twins interact and what this cine lets us do is see their positions in relation to each other and how much space they have, how much space they occupy, and how they might move around and push each other out of the way. So that's something that you can see snapshots of on ultrasound and small parts of it, but you don't get the view of the whole room, as it were, the room being the womb," she said.
Whereas conventional MRI takes snapshots of thin slices of the body as it penetrates through it, so-called cinematic-MRI (or cine-MRI) takes repeated images of the same slice, before stitching them together to create a video.
"What we do differently is much thinner slices of the brain, so the pictures that we take are much, much thinner, just a couple of millimeter thickness regions and we overlap them, so that means that even if the baby moves we've over-sampled the brains, so when we come back to looking at them then if we want to reconstruct the 3D volume of the brain we've got extra data, which means we're not missing out any key regions," said Taylor-Clarke.
Taylor-Clarke has been using the technique to study TTTS, a relatively common complication in which the blood supplies of twins sharing the same placenta become connected. TTTS occurs when blood moves from one twin to the other. The twin that loses the blood is called the donor twin and the sibling that receives it is called the recipient twin. As the twin receiving its sibling's blood grows larger, the growth of the donor twin becomes stunted. In the worst cases it can prove fatal to both twins.
"We use MRI in twin-to-twin transfusion syndrome, not so much for diagnosing it, which can effectively be done on ultrasound but more for looking at the consequences of it, so one of the problems with the imbalances of blood flow is that if you get a sudden shift of blood from one twin to the other, that can cause brain injury, so it can cause stroke or hemorrhage in one or both of the twins' brains. MRI can pick up signs of brain injury much earlier and in much greater detail than ultrasound can at the moment," Taylor-Clarke explained.
Some twins who seemed to have normal brains when screened using ultrasound showed differences in brain volume when examined using MRI. Ultimately the team hopes to develop a tool that could accurately predict developmental problems in advance of birth, meaning parents could be given extra support once the twins are born.
But Taylor-Clarke is not advocating cine-MRI scanning to be used during routine pregnancies.
"I think MRI scanning is a very specialized technique and the vast majority of women have healthy pregnancies without any problems and deliver well, healthy babies and if we were to scan all pregnant women we would pick up a very very small number of abnormalities and potentially pick up things that we didn't know how to interpret that might be quite stressful for some mothers," she said.
For sufferers of TTS, foetal laser surgery may be done to interrupt the flow of blood from one twin to the other, allowing the fluid imbalance to correct itself. After birth, if TTS is mild, full recovery is expected for both babies. However, severe cases may result in the death of a twin.