The rate of cervical change and the phenotype of spontaneous preterm birth.Iams JD, Cebrik D, Lynch C et al (2011) 205(2) 130.

This was a prospective, multicentric observational study carried out in the maternal and fetal research units' research networks from 1992 to1994. In this study, patients were followed prospectively from 24 weeks on two occasions, separated by four weeks. Ultrasound scans were used to measure the cervical length. The aim was to detect the slope of shortening in the cervical length, which occurred in patients presenting later with either spontaneous preterm labour or preterm rupture of membranes.

Patients were classified into two main groups: (a) preterm delivery group where they were subdivided into three other groups (spontaneous preterm labour, preterm rupture of membranes and preterm delivery for medical/obstetrical indication) and (b) term delivery group.

There was a clear objective of the authors as to compare the spontaneous preterm group with the preterm premature rupture of membrane group. This was done with respect to the rate of cervical shortening before delivery. The hypothesis was that: the rate of the cervical shortening was the similar.

Although the different groups were highlighted, and there was a comparison between the spontaneous preterm group and the indicated preterm group on the one hand; and between the term group on the other hand, this was not mentioned in the abstract. In addition to this, the scanning was done in two weekly intervals and not in four weekly as stated in the abstract.

Furthermore, an additional hypothesis was added in the course of the study design: that the rate/slope of cervical change before term delivery or indicated preterm birth, would differ from spontaneous preterm delivery.

The study used relatively old data (from 1992 to 1994), the ultrasound machines used were not stated, and the cases were not adjusted for factors like age, prior obstetric risk factors, obstetric history or parity.

Simple non repetitive style was used and a simple graph with a curve showing the slope was easy for the reader to understand. P values were used in the analysis. The mean cervical length shortening in mm/week was also mentioned.

The proportion of patients with incomplete follow-up who were excluded was not stated. Also, it was stated that the number of preterm spontaneous rupture of membranes were mostly African American, and multiparous women with prior preterm birth.

The proposal is that cervical sonography be used as a predictive tool for these phenotypes (presentations). The short cervix in midtrimester is suggested as an effect of early labour rather than cervical incompetence problem. Clearly, the question regarding other presentation of preterm labour still needs to be explored.