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First and second-trimester biochemical markers of chromosomal anomalies and their relationship to maternal haemoglobin levels

N J Cowans, K Spencer
Prenatal Diagnosis 2005, 25 (8): 693-9
16050001

OBJECTIVE: To evaluate a previous hypothesis that maternal serum biochemical markers used in the assessment of Down syndrome risk are related to maternal haemoglobin concentrations.

METHODS: A series of 1306 second-trimester prenatal screening records were retrieved including information on marker levels (AFP and fbetahCG MoMs), Down's risk, a priori age risk, maternal weight and maternal height. Each individual record was merged with data from haematological investigations on samples collected on the same day. A similar series of 1688 first-trimester screening records were also retrieved including the maker levels for PAPP-A, and fbetahCG MoMs were merged with data from haematological investigations carried out on the same day. The two groups were categorised according to their haemoglobin levels; anaemic (less than 11.0 g/dL in first trimester and 10.5 g/dL in the second trimester), high haemoglobin (greater than 14.0 g/dL and 13.2 g/dL) or normal (between these ranges). An analysis was made of marker levels in the various groups before and after correction for ethnicity and of the screen-positive rate in the various groups. Using a formula based on maternal height and weight, variation of marker levels with plasma volume was assessed.

RESULTS: In the first trimester, 12.6% of the pregnant population was anaemic and 1.6% had elevated haemoglobin levels. In the second trimester this was 12.7 and 3.9%. These figures varied considerably with ethnic origin, with Asian and Afro-Caribbean women being more anaemic than Caucasian women. Haemoglobin levels declined by 7% between the 11- and 21-week period. Maternal plasma volume (as calculated by a widely used maternal height and weight relationship) was not correlated with weight-corrected biochemical marker MoMs in either trimester. A weak but significant correlation of maternal plasma volume and haemoglobin concentration was observed. There was no significant correlation between biochemical marker MoMs and haemoglobin concentration. Although the proportion of pregnancies designated screen positive decreased as haemoglobin levels increased, this was paralleled by a decrease in the maternal age a priori risk.

CONCLUSIONS: There is no relationship between maternal haemoglobin levels and the levels of Down syndrome markers in either the first or second trimester. Biochemical marker levels do not need to be corrected for haemoglobin concentrations when used in screening for Down syndrome.

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