Table 3. Relationship between glomerular filtration rate (GFR in pregnancy and birth weight, estimated in three studies.
Study | n of subjects | Gestational age (wks)when GFR estimated | mean GFR(ml/min) | β g bw/GFRratio a | SE (β) | Partial rb |
Gibson2, 1973c | 20 | 28 | 152 | 1603d | 784e | 0.44 |
Dunlop4, 1981c | 25 | 26 | 152 | 67d | 535f | 0.03 |
Present study, MDRD | 953 | 18 | 124 | 103 | 51 | 0.07 |
Present study, CG | 953 | 18 | 162 | 118g | 57 | 0.07 |
GFRratio is the ratio of subject i’s GFR to the mean GFR. We used this metric to compare results across studies to adjust for differences in gestational week when GFR was measured.
Partial r is partial correlation coefficient.
measured GFR using inulin clearance.
The beta and partial r for Gibson and Dunlop studies were calculated conditional on gestational age at birth, using the raw data in the original publications.
Gibson had three SGA infants; their inclusion probably accounts for why that study had sufficient power to detect a birth weight-GFR relationship.
The subjects in the Dunlop study had a narrow range of birth weights, and that may explain why the standard error is relatively large in that analysis.
Taking the intraclass correlation coefficient (ICC) for creatinine into account gives a corrected β (SE) for the CG formula of 155 (75) (see text).