Identifying potential problems
The thicker the fluid that accumulates behind the neck of a foetus, the higher the risk of abnormal babies.
But despite this, a majority of foetuses with slightly thickened fluid are born normal, said Dr Tony Tan, an obstetrics and gynaecology specialist .
The thickness of the fluid at the back of a developing baby's neck is known as nuchal translucency.
It is usually measured at between 11 and 14 weeks into the mother's pregnancy, said Associate Professor Su Lin Lin.
The senior consultant at the National University Hospital Women's Centre added that an increased nuchal translucency usually refers to a measurement greater than 3mm.
When the mother is 18 to 22 weeks into her pregnancy, this fluid is measured as nuchal fold instead of nuchal translucency.
"Thickened nuchal translucency or nuchal fold may be associated with chromosomal abnormalities, structural abnormalities, genetic syndromes or foetal infections," said Dr Tan, a consultant at Raffles Women's Centre.
Although chromosomal abnormalities and structural abnormalities can be detected through tests and scans by the second trimester, genetic syndromes and foetal infections are more difficult to diagnose, Dr Tan said.
"There are many types of genetic syndromes and infections that one can check for...
"A baby with normal chromosomal study may still have a genetic syndrome as the genetic abnormality is too small to be seen in a chromosomal study," he explained.
He added that more advanced tests may be required to find the genetic syndrome.
As for the fluid accumulation, Dr Tan said it usually disappears by itself at birth and has no form of direct implication.
He advised parents to discuss the implications with obstetricians or those with special interests in foetal medicine when they detect fluid collection.