pH of vaginal secretion is varied according to the levels of estrogen. Vaginal pH is MOST acidic during:

The pH of the normal vagina ranges between 4-5. Variation depends upon oestrogenic activity. The considerably increased volume of cervical secretions within the vagina during pregnancy consists of a somewhat thick, white discharge. The pH is acidic, varying from 3.5 to 6. This results from increased production of lactic acid from glycogen in the vaginal epithelium by the action of Lactobacillus acidophilus. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 5. Maternal Physiology. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y.Spong (Eds), Williams Obstetrics, 23e.