- Threat of preterm labour (PTL) occurring between 24 and 34 WOA, defined according to validated criteria i.e. by (1) the presence of regular uterine contractions, lasting at least 30 seconds at a frequency ≥ 4 contractions every 30 minutes and confirmed by an external tocogram, (2) a cervical dilation of 3 cm or greater, to focus on true preterm labour, for the nulliparous women and 1-3 cm among primiparous women or multiparous and (3) a cervical obliteration >50%, or a cervix less than 25mm according to the echography, when this information is available. The first two criteria being mandatory, the third one optional as it is more subjective, or less likely to be available for every patient.