RUG has considered
evidence on methods of pregnancy dating (menstrual history
vs ultrasound scan) and has concluded that the method
of choice, in pregnancies where at least one ultrasound
has been done by 22 weeks gestation, should be by ultrasound
biometry. There is no evidence for policies which use
LMP dates, even if they are within 4,7,10 or 14 days
etc within the scan dates. LMP dates are often wrong,
as they do not accurately reflect the day of conception
i.e. the actual age of the baby. The arguments are summarised
here and referenced in one of our Perinatal
From 2003, all West Midlands units are now dating
pregnancies by ultrasound alone.
Funding was identified nationally to
aid the National Screening Committee’s programme
for antenatal screening. The allocation to the West Midlands
was distributed by the Perinatal Institute to all units
to purchase ultrasound equipment. In
smaller units, where there would not be a sufficient
allocation to buy equipment, Trusts had made a commitment
to pay the shortfall. In most cases, these monies had
been used to elicit extra funding from Trusts; the regional
allocation of £337,000 generated an additional
£241,000 in funding for equipment.
In February 2005, the Regional Ultrasound Group agreed that the regional recommendation for charts would be Robinson and Fleming* for crown rump length.
In September 2008, the National Screening Committee produced a statement on crown rump length conversion. It is in line with existing recommendations from the British Medical Ultrasound Society (BMUS) and the Regional Ultrasound Group (RUG) in recommending the use of Robinson and Fleming charts. However, the data within the paper have been revised and the equation produced is different to that used previously.
Gestational age (days) = 8.052*SQRT(1.037*CRL)+23.73
*Robinson HP and Fleming JE. A critical evaluation of sonar "crown-rump length" measurements. British Journal of Obstetrics & Gynaecology. 82(9):702-10, 1975 Sep.