The pregnancy cohort
A total of 2,259 pregnant women were included in this analysis. The mean (SD) age of the study sample was 28.4 (5.3) years. The numbers of pregnant women in their first, second and third pregnancies were 508 (22.5%), 834 (36.9%) and 619 (27.4%), respectively. sCr in the pregnancy cohort was reasonably normally distributed (skewness 0.067) with a mean (SD) of 53.2 (8.7) μmol/L. The 97.5thpercentile for the SC in the first trimester was 70.9 μmol/L. The mean (SD) eGFR was 123.4 (10.7) mL/min/1.73 m2, with a median of 123.5 (IQR 118.1-144.0) mL/min/1.73 m2. During the follow-up at 24-30 weeks of PoG (992 pregnant women), the mean SC (SD) was 48.0 (8.2) μmol/L, with a slightly skewed distribution (skewedness 1.9). The 97.5th percentile for sCr from 24-30 weeks was 65.2 μmol/L. The mean (SD) eGFR was 127.4 (9.6) mL/min/1.73 m2 , with a median of 127.9 (IQR 122.4-133.8) mL/min/1.73 m2.
From the 4th-5th week of PoG, SC continued to decrease steadily until the completion of 12 weeks (Figure 1). At the 24th week, a further decline in sCr was observed, and it started to increase after the 25thweek. The respective eGFR values followed the inverse pattern, with the highest value at approximately the 24th week. Homogenous subsets of sCr values according to PoG were prepared for further analysis using one-way ANOVA (Table 2). In these groups, a one-way between-group ANOVA was conducted to explore the impact of PoG on sCr. There was a significant difference in sCr for the three groups [F (4,3250)=95.703, p<0.001]. The effect size calculated using eta squared was 0.105 (medium to large effect). Post hoc comparisons using Tukey’s HSD test indicated that the mean sCr for each PoG group was significantly different from that of other adjacent groups.
As age showed an effect on sCr in the nonpregnant cohort, the values of the pregnancy cohort were further analysed according to age categories. After the initial descriptive analysis and subset analysis, participants were divided into two groups according to their age (Group 1: less than 35 years; Group 2: 35 years and above). Using a two-way ANOVA for age and PoG, the interaction effect between PoG and age group was found to be marginal [F(4,3251)=2.331, p=0.054]. There was a statistically significant main effect for PoG [F(4,3251)=45.112, p<0.001], and the effect size was small to medium (partial eta squared=0.052). Post hoc comparisons using Tukey’s HSD test indicated that even after including age in the model, the mean sCr for each PoG group was significantly different from that of the adjacent groups. The main effect of age [F(1,3251)=5.760, p=0.016] was also significantly different across age groups, with a small effect and higher sCr for the age group of 35 years and above.
To further assess the changes in renal functions using the cohort design, a one-way repeated-measures ANOVA was conducted. This analysis was conducted only for those who had follow-up data at 24-27 weeks of PoG, in which the lowest sCr was observed (n=524). Three groups were defined according to the PoG at the time of recruitment as above. The mean (SD) values of the first and second measures are presented in Table 3. There was a significant reduction in sCr with advancing pregnancy [Wilks’ Lambda=0.71, F(1,521)=211.202, p<0.001, multivariate partial eta squared=0.288]. This analysis showed that despite having different mean values based on the PoG, at 24-27 weeks, the PoG values were concentrated around a mean value of 47 μmol/L.