Dark adaptation pattern of pregnant women as an indicator of functional disturbance at acceptable serum vitamin A levels.

BACKGROUND

As a result of lack of precise guidelines, nutritional surveys on adults and high-risk groups are using diverse reference values as a dividing line between normal and deficient vitamin A status.

OBJECTIVE

To investigate whether pregnant women at marginally normal serum retinol status exhibit functional alteration that are characteristic of a deficiency state.

SETTING

Antenatal clinic, Gondar teaching hospital.

SUBJECTS: Ninety-six healthy pregnant women were recruited for the study at the antenatal clinic.

INTERVENTION: The dark adaptation time was tested in 48 pregnant women with marginal serum retinol level. The time lapse to see successive light stimuli of diminishing luminescence grade and change in retinal sensitivity pattern was measured using dark adaptometer. Results were compared with the results of a control group of women of similar age, parity and gestational period but with serum retinol values above 35 microg/dl.

RESULTS

The mean serum retinol levels of cases and controls were 23.35 microg/dl and 40.47 microg/dl respectively (P<0.008). Cases have a lower dark adaptation than their controls, shown by their remarkably reduced sensitivity to light. For instance at mean final light threshold was -2.20+/-0.11 log cd/m(2) in cases as compared to -2.88+/-0.1 log cd/m(2) in the normal group (P<0.001).

CONCLUSION

During pregnancy, dark adaptation was strongly associated with serum retinol concentration and women with marginal vitamin A concentration had lower dark adaptation. Hence marginally normal serum retinol levels should be categorized as a deficiency state, at least in pregnant women.