Dr Raine-Fenning, an Associate Professor of Reproductive Medicine and Surgery and one of the senior Consultant Gynaecologist working at Nurture Fertility, led the research which was conducted by one of his PhD students, Dr Shyamaly Sur, a clinical research fellow and specialist in Obstetrics and Gynaecology. Together, and with support from the Unit, they tested two hypotheses; twins grow more slowly than singletons in the womb and that restricted or slow growth in the first trimester (from conception until 13 weeks) can predict miscarriage.
The team tracked the growth of 247 singleton and 264 twin embryos conceived through IVF, allowing them to know the embryos’ precise gestational age. for each embryo, the crown-rump length (CRL; distance from top of the embryo’s head to the bottom of its buttocks) was measured from a transvaginal (internal) ultrasound scan and the pregnancy then monitored until birth. Using these measurements, the researchers developed two growth curves to test their hypotheses; one to record the growth of singleton embryos and another chart specifically for twin embryos. The results, which were recently presented at the British Fertility Society (BFS) meeting in Leeds, were interesting and drew the attention of national experts and the media. They showed that for singleton pregnancies, slow growth in the first trimester was a sensitive predictor of subsequent miscarriage, 78% (34 of the 44) singleton pregnancies that miscarried were growth restricted, whilst 98% of singleton pregnancies that did not miscarry were not growth restricted. This was not the case in twin pregnancies, however, where only 29% (12 of 42) of pregnancies that miscarried were growth restricted although a similar number of twin pregnancies that did not miscarry were not growth restricted.
These results show that we can potentially identify singleton pregnancies at higher risk of miscarriage through accurate measurement of growth during the first trimester. The next step in this research is to examine the relationship between restricted growth and miscarriage in more detail to explain the reasons behind this relationship. This is something that Dr Raine-Fenning and his team are already doing.
Dr Raine-Fenning explains:
“This study and its results are interesting and shed some light on the factors that underlie miscarriage. Many people believe that twin embryos grow more slowly in early pregnancy than singletons and reassure people that this is not a negative finding. Our work actually shows that twin embryos grow at the same rate as singleton embryos in the early stages of pregnancy and if one or both of the embryos are exhibiting slow growth this should be taken seriously and further assessments arranged.
Our study also provides the clearest evidence yet that restricted growth in single embryos during the early stages of pregnancy is related to subsequent miscarriage in that pregnancy. Our method of following women who have undergone IVF treatment meant that we were able to accurately date the pregnancies and were, therefore, able to relate their subsequent growth to the date of conception very precisely. This is not possible in spomtaneous pregnancies as the exact date of conception is never known and simply estimated from the date of the last menstrual period.
IVF provides the perfect model to study early growth but further work is required to ensure IVF pregnancies, both singleton and twin, grow at the same rate as spontaneously conceived pregnancies. This is not easy but is something we are trying to assess at Nurture Fertility. We hope that this work will go towards developing a new system to identify pregnancies ar risk of miscarriage. More research is now needed to investigate the relationship between growth and the underlying causes of miscarriage in more detail. At Nurture Fertility, for example, we are focussing on how blood flow to the womb lining and embryo quality influence conception rates and subsequent miscarriage. It is important to remember that there are many causes of miscarriage and these findings only consider one aspect of the problem. Nevertheless, the findings are interesting and provide insight into embryo growth.”
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