British Journal of Haernatology, 1982, 50, 423-425

Changes in the mean corpuscular red cell volume in women with p-thalassaemia trait during pregnancy

D. LEWIS, R. J. STOCKLEY A N D I. CHANARIN Clinical Research Centre and Northwick Park Hospital, Harrow

Received 28 August 1981: accepted for publication 12 October 1981

SUMMARY. Thirty-eight women with p-thalassaemia trait and thirty-five normal Asian women were studied retrospectively during normal pregnancies. The red cell size increased in both groups, with a mean increase of 2.3 f l (SD 2.3) in the women with B-thalassaemia trait and a significantly higher increase of 4.3 f l (SD 2.1) in the normal Asian women. The rise in red cell size during pregnancy which is a physiological change, is thus impaired by defective globin-chain synthesis as well as by iron deficiency.

An increase in red cell size occurs during normal pregnancy and may lead to macrocytosis (Chanarin et al, 19 77). The physiological mechanisms involved have not been elucidated but are masked by iron deficiency. This study investigates the effect of impaired globin-chain synthesis on this process.

METHODS

A retrospective study on the variation of size of red blood cells of 38 healthy pregnant women with p-thalassaemia trait and 3 5 healthy pregnant Asian controls, all with uncomplicated pregnancies, was undertaken. All but one of the women with P-thalassaemia trait were Asian (Indian) and one was Chinese. fl-Thalassaemia trait was diagnosed by haemoglobin electrophoresis, all patients having a HbA? level greater than 3.5%, accompanied by a reduced mean corpuscular volume (MCV). All women received oral iron and folic acid prophylaxis and had blood samples taken at booking at the antenatal clinic, 28 and 36 weeks of pregnancy or thereabouts. The data were analysed in three groups: 12-20 weeks, 24-32 weeks and 33-36 weeks. Haemoglobin, red cell count (RBC), mean corpuscular volume (MCV) and mean cell haemoglobin (MCH) were measured on the Coulter Counter Model S.

Correspondence: Dr D. Lewis, Department of' Haematology, Clinical Research Centre and Northwick Park Hospital, Watford Road, Harrow, Middx HA1 3UJ. 0007-1048/82/0300-0423$02~00 @ 1982 Blackwell Scientific Publications

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42 4 D. Lewis, R. 1. Stockley and I. Chanarin

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RESULTS

Haernoglobin and red cell count

The mean haemoglobin in the women with P-thalassaemia trait at booking was 10.6 g/dl, between 24 and 32 weeks pregnancy was 9.8 g/dl and between 32 and 36 weeks pregnancy was 10.7 g/dl. In the normal Asian group, the mean haemoglobin at booking was 12.6 g/dl, between 24 and 26 weeks pregnancy was 12.3 g/dl and between 33 and 36 weeks pregnancy was 12.7 g/dl. The red cell counts matched the haemoglobin levels (Table I).

Table I. Blood indices during pregnancy in 38 women with p-thalassaemia trait and 35 haematologically normal Asian women

Hb (g/dl) MCV (fl) RBC ( x lo6/$) MCH (pg)

Weeks P-Thalass- p-Thalass- p-Thalass- p-Thalass- pregnant aemia Normal aemia Normal aemia Normal aemia Normal

12-20 10.6 12.6 67 85 5.14 4.40 20.6 28.9 24-32 9.8 12.3 68 89 4.84 4.13 21.2 29.8 33-36 10.7 12.7 68 88 5.08 4.27 21.2 29.6

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Weeks pregnant Fig 1. The mean corpuscular volume during pregnancy in 38 women with P-thalassaemia trait (0) and in 3 5 haematologically normal Asian women (0).

Red Cell Volume in J?-Thalassuemia Trait during Pregnancy 42 5

Mean corpuscular volume ( M C V )

At booking the mean MCV of the 8-thalassaemia trait group was 67 fl(66.6, SD 4.0) which rose to 68 fl(68.4, SD 3.8) at 24-32 weeks with no further change at 33-36 weeks. In the normal Asian group the mean MCV was 85 fl(85.3, SD 3.2) at booking, rose to 89 fl(88.5, SD 3.4) at 24-32 weeks and was unchanged thereafter (Fig 1).

Analysis of the rise in MCV in individual women by ‘Student’s’ t test was also performed. There was a mean increase during pregnancy of 2.32 SD 2.31 (or 3*63%rise, SD 3.46) in the P-thalassaemia group and a mean increase of 4.26 SD 2.05 (or 5.05%, SD 2.45) in the normal Asian group. These increases in MCV (both absolute and expressed as percentage rise) were significant in both groups (P<0.001 1. However, there was also a statistically greater rise in the normal Asian group than in the /j-thalassaemia trait group (P value between 0.01 and 0.001).

DISCUSSION

The data confirm earlier reports that there is a physiological increase in red cell size which averages 4 fl during normal pregnancy. Women with P-thalassaemia trait also show an increase but the increment is significantly smaller than a comparable group. This would suggest that abnormal globin-chain synthesis, as well as lack of iron, interferes with the normal physiological mechanisms that are responsible for this increase.

ACKNOWLEDGMENT

We are grateful to Mr A. Fisher, Mr H. Gordon and Mr I. McFadyen for allowing us to use data from their patients.

REFERENCE

CHANARIN, I.. MCFADYEN, I.R. & KYLE, R. (1 977) The physiological macrocytosis of pregnancy. British journal of Obstetrics nnd Gynaecology. 84, 504-508.