I am a Phd student currently working on biomarkers during pregnancy and am unsure which test to use.

I want to assess whether there are significant differences in my biomarker at the beginning of pregnancy compared to a time point later on.

From experience and also a Pearson's correlation analysis I conducted, I know that there are several potential confounders for my biomarker due to changes during pregnancy (f.i. renal function changes in pregnancy).

When not correcting for confounders (I am using SPSS) I know to use a simple paired samples T test (which was significant: p<0.001)

However, I think it would be very sensible to correct for at least 4 or 5 variables that change during pregnancy. Which test should I use?

--> I tried univariate ANCOVA (biomarker as dependent variable, time points as fixed factors, covariates as covariates), however, I am unsure about the validity of the results as my parameters are dependent and one of the prerequisites of ANOVA is to have independent variables.

--> I also tried a repeated measure ANCOVA, however, I do not have any groups to compare just one variable (continuous) and 2 time points...

Is there any other way I missed? Is any of the options above ok to use?

Would appreciate any help very much!

Thanks