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.