British Journal of Obstetrics and Gynaecology March, 1971. Vol 84. pp 205 -209

RELATIONSHIP BETWEEN FETAL URINE PRODUCTION AND AMNIOTIC FLUID VOLUME IN NORMAL PREGNANCY AND PREGNANCY COMPLICATED BY DIABETES BY

L. C. VAN OTTERLO J. W. WLADIMIROFF AND

H. C. S. WALLENBURG Department of Obstetrics and Gynaecology, Academic Hospital Rotterdam-Dijkzigt Dr Molewaterplein 40, Rotterdam, The Netherlands Summary The hourly fetal urine production rate (HFUPR) was calculated from ultrasonic measurements of fetal bladder volume. A normal HFUPR reference curve, constructed from measurements in 189 normal pregnancies between 24 and 42 weeks gestation, showed a rapid increase of HFUPR from 3 .3 to 24.4 ml up to 40 weeks followed by a slight decline. The amniotic fluid volume was estimated by the p-aminohippuric acid method within 12 hours of HFUPR measurements. In 67 normal pregnancies, there was no relationship between HFUPR and amniotic fluid volume measured between 36 and 41 weeks gestation. In 12 patients with fetal growth retardation, a relationship was found between reduced fetal urinary output and low amniotic fluid volume between 36 and 38 weeks gestation. In the 16 diabetic patients studied between 28 and 40 weeks gestation, there was no relationship between HFUPR (within or below normal range) and the high amniotic fluid volume (above 1500 ml in 13 patients). The implications of these findings are discussed.

computation of the hourly fetal urine production rate (HFUPR; Campbell et al, 1973). A group of 189 normal pregnancies between 22 and 42 weeks gestation was studied in order to construct a reference curve of the normal HFUPR (Van Otterlo, 1976). Figure 1 shows the relationship between HFUPR and the gestational age of the fetus. Between 25 and 40 weeks a rapid increase in mean HFUPR from 3.3 to 27.4 ml can be observed. Between 40 and 42 weeks there appears to be a reduction in HFUPR. Amniotic fluid volume was estimated by means of the p-aminohippuric acid method (Charles and Jacoby, 1966). In two cases the

ULTRASONICmeasurement of fetal urine production (Campbell et d,1973; Wladimiroff and Campbell, 1974) presents the possibility of studying the relationship between fetal urinary output and amniotic fluid volume (Wladimiroff et al, 1975a and b). We present data on this relationship in normal and complicated pregnancies. METHODS Fetal bladder volume was calculated from the largest longitudinal and transverse bladder dimensions (Campbell et al, 1973). The increase in bladder volume over a period of one hour during the process of bladder filling allowed 205

206 35

VAN OTTERLO, WLADIMIROFF AND WALLENBURG

-1

,

L , 24

26

28

30

I

l

l

1

1

32

34

36

38

40

1

42

the Tables of Kloosterman (1970), corrections being made for maternal parity and the infant’s sex. In the second group, there were 12 patients of between 36 to 38 weeks gestation with fetal growth retardation and infants whose birth weight was below the 10th centile (Kloosterman, 1970). The third group comprised 16 patients of between 28 to 40 weeks gestation in whom an oral glucose tolerance test with a 50 g glucose load showed diabetes according to the criteria of Kobberling and Creutzfeldt (1970).

gertationol age ( w k r )

FIG.1 Hourly fetal urine production rate (HFUPR) in relation to gestational age in 189 normal pregnancies between 22 and 42 weeks gestation. The upper limit represents the 95th centile, the lower limit the 5th centile.

amount of amniotic fluid was too small to be measured by this means. The actual volume was measured during Caesarean section in one patient and after low amniotomy in another. The time interval between the measurements of HFUPR and amniotic fluid volume was less than 12 hours in all cases. PATIENTS Three groups of patients were studied: all were certain of the date of onset of their last menstrual period. In the first group, there were 67 women with normal pregnancies varying from 36 to 41 weeks. i n this group, the birth weights were between the 10th and 90th centile according to

RESULTS Normal pregnancy (n = 67) Table I shows the mean value and range for HFUPR and amniotic fluid volume for each week of gestation between 36 and 41 weeks. The mean HFUPR varied from 17.5 ml at 36 weeks to 25.7 ml at 40 weeks, the mean amniotic fluid volume varied from 660 to 949 ml. Between 40 and 41 weeks gestation, a slight reduction in mean HFUPR was accompanied by a distinct drop in mean amniotic fluid volume. Figures 2, 3 and 4 show the relationship between HFUPR and amniotic fluid volume for each week of gestation between 36 and 41 weeks. Fetal growth retardation (n = 12) In Table i I detailed data on the 12 patients with fetal growth retardation are given; in nine of them there was vascular placental insufficiency. In 11 patients, HFUPR was

TABLE I Mean value and range for hourly fetal urine production rate (HFUPR) and amniotic fluid volume between 36 and 41 weeks gestation

No.

12 13 10 12 10 10

HFUPR (ml)

Amniotic fluid volume (ml)

Gestational age (weeks)

Mean

Range

Mean

Range

36 37 38 39 40 41

17.5 19.9 22.7 25.2 25.7 22.6

13-23 14.5-30 18-29 19-31 20-30 16-31

660 875 832 807 949 415

380-1000 330-1475 430- 1245 425-1475 450-1475 50- 925

207

FETAL URINE AND AMNIOTIC FLUID IN DIABETES H.F.U.P.R. fmli 36 weeks; N

,I

12

H.F.U.P.R.

1

(mll

N

37 ,:ew

~

13

I

I

40 weeks, N

10

I

41 weeks; N

10

1

1000

1500

130

0

--I

I

I

0

0.

I

i 1

0

10

lo

500

1000

500

0

1000

1500

A.F .V. ( m i )

500

FIG.2 Relationship between HFWPR and amniotic fluid volume at 36 and 37 weeks gestation. The horizontal lines represent the 5th and 95th centile of the normal HFUPR curve.

H.F.U.P.K 'ml"

I -

.

.

'

38 weeks; N

10

I

39 weekr; N

I

12

30 r +

500

1000

0

500

1000

1500

A.F.V. ( m l )

FIG.3 Relationship between HFUPR and amniotic fluid volume at 38 and 39 weeks gestation. The horizontal lines represent the 5th and 95th ceiitile of the normal HFUPR curve.

below the 5th centile of our normal curve, and in 9 patients the amniotic fluid volume was below 425 ml.

Diabetes mellitus (n = 16) Table I11 gives detailed data about the 16 mothers with diabetes. Eight patients had normal blood sugar levels and eight had raised

I000

0

500 A.F.V. ( m l i

FIG.4 Relationship between HFUPR and amniotic fluid volume at 40 and 41 weeks gestation. The horizontal lines represent the 5th and 95th centile of the normal HFUPR curve.

blood sugar levels at the time of HFUPR and amniotic fluid volume measurement. HFUPR was mostly within, and sometimes below, the normal range. Polyhydramnios (an amniotic fluid volume of more than 1500 ml) was observed in all eight untreated diabetics and in three of the treated patients. DISCUSSION Amniotic fluid volume depends on the production of water and solutes and the exchange between the fetal and maternal compartments. The data from our present study show that between 36 and 41 weeks gestation there is no relationship between fetal urine production and amniotic fluid volume. Many investigators observed a fall in amniotic fluid volume after 37 to 38 weeks gestation (Gadd, 1966; Queenan et al, 1972). In our study, amniotic fluid volume showed an increase between 36 to 37 weeks, a slight decrease between 37 to 39 weeks and, apart from an unexpected rise between 39 and 40 weeks, a further marked decrease beyond 40 weeks of gestation. Fetal urine production showed an increase up to 40 weeks and a slight reduction thereafter. The same trend was observed in our normal curve (Fig. 1). Of

208

VAN OTTERLO, WLADIMIROFF AND WALLENBURG

TABLE I1 Data on the I 2 patients with fetal growth retardation No.

Gestational age (weeks)

1 2 3 4 5

36 36 36 37 31

6 I 8 9 10 11 12

37 31 37 38 38 38 38

HFUPR (mu

Complications Congenital toxoplasmosis Trisomy 21 Pre-eclamptic toxaemia Pre-eclamptic toxaemia Placental infarction Placental infarction Placental infarction Pre-eclamptic toxaemia Placental infarction Pre-eclamptic toxaemia Placental infarction Pre-eclamptic toxaemia, placental infarction

19 7 8 14 11 10 10.5 5 19 9 7 5

Centile*

Amniotic fluid volume (ml)

5-95