There are several signs suggesting that labour might be starting. These include:

  • Irregular contractions, known as Braxton-Hicks contractions occurs prior to real labor contractions. They are usually milder than those of true labor and may come more often as you get closer to your due date.
  • A "show," i.e., when the plug of mucus from your cervix (entrance to your womb or uterus) comes out
  • Backache
  • An urge to go to the toilet, which results from your baby's head pressing on your bowel
  • Your water breaks (rupture of membranes)

What do contractions feel like?

  • During contraction, your womb tightens and then relaxes. In some women, contractions may feel like extreme pains similar to that experienced during menses. 
  • As labour proceeds, your contractions tend to become longer, stronger and more frequent.
  • During a contraction, the muscles tighten, and the pain worsens.
  • If you place your hand on your abdomen, you'll feel it getting harder; when the muscles relax, the pain fades, and you will feel that the hardness is easing.

Backache often comes on in labour

  • You may experience backache or the heavy, aching feeling similar to that experienced during menses.

A "show" can signal the beginning of labour

  • During pregnancy, there is a mucous plug in your cervix, which comes away just before labour starts or during early labour, and you may pass it out of your vagina. This small amount of sticky, jelly-like pink substance is called a show.
  • It may come away in one splash or in several pieces.
  • It's pink in colour as it's bloodstained.
  • It's normal to lose a small amount of blood mixed with the mucous. 
  • Some women don't have a show.

Source:

Signs that labour has begun-Your pregnancy and baby guide[Internet]. Available at: https://www.nhs.uk/conditions/pregnancy-and-baby/labour-signs-what-happens/. Accessed on Mar 13, 2020.