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

^aGFR_ratio 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.

^bPartial r is partial correlation coefficient.

^cmeasured GFR using inulin clearance.

^dThe 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.

^eGibson had three SGA infants; their inclusion probably accounts for why that study had sufficient power to detect a birth weight-GFR relationship.

^fThe 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.

^gTaking the intraclass correlation coefficient (ICC) for creatinine into account gives a corrected β (SE) for the CG formula of 155 (75) (see text).