Premature labour
The signs of premature labour can be similar to the signs of labour that starts at full term, and may include: contractions, period-type pains, breaking of the waters, etc.
Your midwife or doctor should discuss with you the symptoms of pre-term labour, and offer checks to see if you're in labour.
Babies born before full term (before 37 weeks) are vulnerable to problems associated with being born premature. The earlier in the pregnancy a baby is born, the more vulnerable they are.