Screening criteria for beta thalassaemia trait in pregnant women

To establish suitable screening criteria for beta thalassaemia trait during pregnancy using an automated blood counter incorporating light scattering technology.

Pregnant women (n = 857) at a London antenatal clinic were investigated for beta thalassaemia trait if the Technicon H.2 full blood count showed either a mean corpuscular volume (MCV) < 85 fl or a mean corpuscular haemoglobin (MCH) < 27 pg. Results were then analysed to establish which of these variables was more suitable for screening and to determine suitable cut off points for calculating the haemoglobin A2 percentage.

The MCH was superior to the MCV for thalassaemia screening as it was a more stable measurement and fewer unnecessary tests were performed. A MCH less than 27 pg is a suitable cut off point for screening. This screening criterion was equally applicable to a Coulter impedance counter.

Pregnant women presenting at an antenatal clinic with a MCH < 27 pg should be investigated further to confirm or exclude a diagnosis of beta thalassaemia trait.