Serial changes in serum uric acid concentrations have been studied in a group of healthy women before conception, at regular intervals throughout pregnancy and finally 12 weeks after delivery. Compared with pre-pregnancy values uric acid concentrations decreased significantly by 8 weeks gestation and this reduced level was maintained until about 24 weeks. Thereafter the concentrations increased such that by term they were greater than the pre-pregnancy values in the majority of patients and remained elevated until a t least 12 weeks after delivery. If clinical management during the second half of pregnancy is to be based on increases in serum uric acid concentrations then such increases will have to be carefully interpreted against the background of rising concentrations which occur as part of the physiological response t o normal pregnancy.Modern clinicians rely increasingly on laboratory tests for the management of patients; for some the stage has been reached when deviation from an accepted range of laboratory values is in itself sufficient reason to justify treatment. The principle is not intrinsically unreasonable but clinical management based solely, or even largely, on such tests implies a confidence in the 'normality' of any given range of laboratory values that is seldom justified.During pregnancy progressive maternal physiological adaptations occur and many biochemical measurements deviate conspicuously from the normal range for males and nonpregnant females. Laboratory ranges specific to pregnancy need to be defined and ideally would be determined in healthy women having uncomplicated pregnancies resulting in the birth of live healthy children; such data are relatively scarce.This paper describes the changes in serum uric acid concentrations throughout normal pregnancy and reports two clinically important aspects. First the values decrease significantly below non-pregnant levels by 8 weeks gestation; second serum uric acid concentrations are not only increased above non-pregnant values by term in many women but remain elevated for as long as 12 weeks after delivery. Such postpartum values should not therefore be used as representative of non-pregnant concentrations.
Patients and methods
PatientsThirty-one healthy women have been studied; the mean age was 28 (range 23-37) years and each was without any adverse medical, surgical or obstetric history. In five of the women uric acid determinations were repeated during a subsequent pregnancy so that data were obtained from a total of 36 pregnancies. Nine women were primigravidae and 27 were multiparae of whom five had had a previous spontaneous abortion and 22 a successful pregnancy. During the time of this study none of the patients developed medical or obstetric complications or required pharmacological agents including salicylates; all gave birth to live, healthy infants.
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Summary
Forty patients have been studied over 96 menstrual cycles during which a blood sample was obtained within five days of the next menstrual period. Two features emerged: circulating concentrations of progesterone and oestradiol could be elevated on the day bleeding began and conversely the levels of these hormones could be low for some days without menstruation occurring. These data suggest there may not be any direct relation between circulating ovarian hormone levels and the onset of menstrual bleeding.
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