Many parents of twins may be wrongly told they are not identical, researchers say today.
Pre-natal scans will show that a mother is carrying twins – and will also give other information that health staff may use to advise whether the twins are identical or not.
This is based on whether the babies share a placenta or not.
However, according to Professor Jane Wardle, of University College London, UK, up to 30 per cent of identical twins develop in two placentas. She says this happens when there is a split within 48 hours of an egg being fertilised.
A survey, reported in BJOG, found that 82 per cent of parents of same sex twins said their knowledge of whether the children were identical came from health professionals, based on the pre-natal scan.
As many as one in seven parents of children aged eight months were wrong about whether their twins were identical, according to the report.
The survey involved more than 1,500 families.
Professor Wardle said: "Finding out if your twins are identical or not is important to parents.
"However our data suggests that there may be a lack of knowledge among some health professionals about both identical and non identical twins having two placentas.
"Parents have the right to the relevant information if it is available. However most parents will understand that it is not always possible to give a specific answer."
Journal deputy editor John Thorp said: "Additional training may be required for health professionals to avoid giving out the wrong information to parents."
van Jaarsveld C, Llewellyn C, Fildes A, Fisher A, Wardle J. Are my twins identical: parents may be misinformed by prenatal scan observations. BJOG February 29 2012; DOI: 10.1111/j.1471-0528.2012.03281.x.
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