Background

Pregnancy is usually associated with increased vascular volume. This is usually considered physiologic rather than pathologic change because the condition easily resolves few minutes after delivery¹⁰. Hypervolemic state will affect the concentrations of certain parameters thus reducing their usual predictive and diagnostic power⁷. Therefore, it may not be proper in all cases to use references deduced from non-pregnant adults to infer in pregnant adult as this maybe misleading. Secondly, the use of radiological technique may help in determining the possible real state of certain organ function in pregnancy irrespective of hypervolemic state¹¹. The present study was designed to assess if the predictive and diagnostic powers of such biochemical parameters like serum urea, creatinine, uric acid, calcium and inorganic phosphate were compromised in pregnant women and possible diagnostic role. The use of ultrasonography may play in revealing the status of the kidney.

Methodology

Subjects: Thirty (30) pregnant women and twenty (20) non-pregnant women with no known history of renal problem were recruited for the present study. They were aged between 20 and 45 years. Blood samples were collected from all the participants and the serum components were extracted for the laboratory analyses of urea, creatinine, uric acid, calcium and inorganic phosphate while the ultrasound was used to obtain the ultrasonograhic status of the kidney. The pregnant women gave informed signed consent. Methods for serum determination of urea was with diacetylmonoxine as modified by Wybenga^8,12.

Study area

Results

The result showed no significant differences in mean (±SD), serum concentrations of urea; creatinine and uric acid between the pregnant woman and non-pregnant women (p>0.1 in each case) Table 1. However, the ultrasonogram showed no difference in the mean parenchymal thickness of 1.9cm left and 1.91 ± 0.2cm. Mean renal length is 80mm and this is not lower than was found in other studies of non-pregnant adult females.

Figure 1

Table 1: Mean ±SD serum concentrations of urea; creatinine and uric acid in pregnant and non-pregnant women.

Discussion

This finding in the present study though limited by low number of participants, did reveal that serum concentrations of urea, creatinine and uric acid retained their predictive and diagnostic value in pregnancy, a more definitive technique that may reveal the impart of the hypervolemic physiologic state in pregnancy is revealed by the ultrasonogram.

In this preliminary report, a normal kidney sonogram is put side by side that of a pregnant patient. Enthusiasm for using renal parenchymal echogenicity in the diagnosis of renal disease has waxed and waned over the years. Increased parenchymal echogenicity in patients in patients with renal disease was first described in the late 1970s². The early index for this biochemical change may rely on the mean parenchymal thickness⁶. This measures the cortex of the kidneys in at least three places viz; the upper pole, mid moiety and the lower pole, all devoid of the sinus as demonstrated on the legends (1 & 2). This is also useful in cases where ultrasound guided biopsies are needed to make meaningful diagnosis of a renal pathology. The mean renal parenchymal thickness (MRPT), normal for our environment is 1.91 ±0.2cm right and 1.95 ±0.19cm on the left. In this study, the Legends are in agreement with the work done in 2002 by Eze C. U et al ⁵ .The study suggests that for our population, kidneys with a renal length lower than 8.5cm and renal parenchymal thickness of 1.4cm or less should not be biopsied⁵.

Obstruction of the lower aorta and the branches causes diminished blood flow to kidneys. Renal plasma flow and glomerular filtration rate begin to increase progressively during the first trimester¹. This parallels the increases in blood volume and cardiac output. The elevations in plasma flow and glomerular filtration result in an elevation in creatinine clearance. After the 12 ^th week of gestation, progesterone can induce dilatation and atony of the renal calyces and ureters. With advancing gestation the enlarging uterus can compress the ureters as they cross the pelvic brim and cause further dilatation by obstructing flow⁷. Ours is a low resource center with no Doppler ultrasound facility, to observe and record the presence of renal artery dilatation or stenosis but a normal cortico-sinus differentiation was observed by all patients. The calyces were normal. The kidney size did not increase but remained at a mean of 110mm right and 116mm left respectively. There was no increase in echogenicity. The patients were nomo-tensive and renal changes associated in renal failure was absent sonograhically.

Hence critical assessment of the impart of hypervolemia of pregnancy on certain organ functions may need the high precision of radiological techniques in combination with biochemical evaluations.

Conclusion

The use of serum urea and creatinine for kidney functional screening has gained a widespread acceptability amongst diagnostic experts ² . However, in cases where there has been a high suspicion of possible kidney functional impairment with inability of any of the usually used biochemical parameter to reveal same, radiological techniques may be used to further confirm such suspicion. The present design being a pilot study did not observe any loss in predictive and diagnostic ability of serum urea, creatinine and uric acid in screening for the kidney functional integrity in pregnant women. Since both the pregnant and non-pregnant women were apparently healthy, the finding in the present study suggest normal functional kidney despite the known hypervolemic usually reported in pregnant women. Ultrasound showed normal cortico-sinus differentiation in all the patients. Ultrasonographic evidence of renal failure lags behind the biochemical changes to the extent that before observable changes occur, serum urea, creatinine and electrolyte status would have indicated renal failure status.