Study design of choice for finding out Diurnal variation of fat in Expressed breast milk (EBM) for preterm babies

Diurnal variation- fat in Expressed Breast Milk- more in the evening as compared to the morning. To perform this study, we only need to take 2-3 samples in 1-2 days in an adequate sample size. Since this study is being performed at a paicular point in time, it is a CROSS SECTIONAL study. - CROSS SECTIONAL STUDY: Done at point of time, neither forward nor backward. Can't calculate strength of association. Gives prevalence Based on primary data . - Ambispective coho study: observations are bidirectional (past and future both) from the time point it begins.