Which of the following is NOT considered a preliminary onset of labor?

Engagement is the process where the fetal presenting part descends and settles into the pelvic inlet. This signifies that the baby is preparing for birth but is not itself an indicator of the onset of labor. Engagement can happen weeks before labor actually commences and is more about the positioning of the baby rather than an immediate precursor to labor.

In contrast, false labor or Braxton Hicks contractions may indicate that the body is preparing for labor, despite not being a sign of labor starting. Lightening refers to the sensation experienced by the mother when the baby drops lower into the pelvis, again suggesting preparation for labor. The loss of the mucous plug or the bloody show typically indicates that the cervix is beginning to change in preparation for labor, which does have a more immediate connection to labor onset.

Since engagement does not directly suggest that labor is imminent, it stands apart from the other options, all of which are more closely associated with the preliminary signs of labor.