Preterm labour is defined as the onset of labour before 37 completed weeks of gestation counting from the first day of the last menstrual period.1 The incidence varies from 10 to 15 per cent of all pregnancies. Despite advances in medicine, the accurate prediction, prophylaxis and management of preterm labour has remained a unique challenge for every obstetrician. Preterm birth is a leading cause of perinatal mortality in India. Though survival has improved with sophisticated neonatal care, the cost of therapy may not be affordable in a developing nation like ours. In addition, survivors of extreme prematurity may still face considerable long term morbidity in later life.

All patients were regularly followed up in our ante-natal clinic, till delivery. The findings of cervical assessment were then correlated with period of gestation at delivery. Preterm delivery was defined as delivery before 37 completed weeks. The statistical analysis was done using paired-t test. Patients developing any high risk factor or requiring delivery for any other obstetric indications were excluded from the study.

All patients were regularly followed up in our ante-natal clinic, till delivery. The findings of cervical assessment were then correlated with period of gestation at delivery. Preterm delivery was defined as delivery before 37 completed weeks. The statistical analysis was done using paired-t test. Patients developing any high risk factor or requiring delivery for any other obstetric indications were excluded from the study.

Majority of the patients were in the age group of 20-30 years. Of the 80 patients, there were 37 primigravidae and 43 multigravidae. Cervical assessment by TVS was done at 23-24 weeks of gestation in all patients.

Table 1 : Cervical length
Parity	No.	Cervical length in MM
Primis	37	36.5
Multis	43	38.4

Average cervical length in primigravidae was 36.5 mm, while it was 38.4 mm in multigravidae.

Table 2 : Occurrence of preterm delivery
Group	Cervical length	No. of patients	No. of Patients delivering preterm	%
A	³ 3 CM	69	5	7.2
B	< 3	11	10	91

According to measurement of cervical length, patients were categorised into two groups, for analysis. Group-A comprised women with cervical length of 3 cm or more, while patients with cervical length of less than 3 cm were categorised as Group - B. Thus, we had 69 women in group A and 11 in group B. All these 80 patients were followed up till delivery.

Table 3 : Correlation with period of gestation at delivery
Group	No. of patients	Preiod of gestation (weeks)
		28-32	33-36	>36
A	69	—	5 (7.3%)	64 (92.7%)
B	11	4 (36.3%)	6 (54.7%)	1 (9%)

The average period of gestation at delivery in group A was more than 36 weeks, while it was 33.36 weeks in group B. Only 5 out of 61 patients (7.2%) had a preterm delivery, all delivering between 33-35 weeks. While in group B, 10 of 11 women (91%) delivered before 37 weeks of gestation. Only 4 of these 10 cases, delivered before 32 weeks of gestation.

Table 3 : Correlation with period of gestation at delivery
Group	Internal os	Nos.	POG in weeks at delivery
			28-32	33-36	>36
	Closed	61	—	—	61
A (N-69)	Open (Funelling)	8	—	5	3
	Closed	2	—	1	1
B (n-11)	Open (Funelling)	9	4	5	—

In Group B 4 of them delivered between 28-32 weeks and 5 delivered between 33-36 weeks. Out of 2 remaining cases without funnelling, one delivered at 35 weeks. Thus, all 9 cases with cervical length less than 3 cm with presence of funnelling delivered preterm (100%).

Due to a diverse aetiopathogenesis, prevention of preterm labour has had limited success. Various studies including nutritional support, health advices, and intensive education have had limited success.
Despite the availability of aggressive treatment protocols and pharmacological interventions, preterm labour remains one of the common causes of perinatal morbidity and mortality. The main reason for low success rates of tocolytic therapy is failure to detect the onset of preterm labour in patients at an early stage. Thus, it becomes essential to identify patients, both symptomatic or asymptomatic, early enough so that optimum treatment in form of tocolysis or cerclage can be attempted along with prophylactic antibiotics.
Preterm labour has certain demographic or obstetric high risk factors. Digital examination of cervix, with assessment of uterine contractions along with these high risk factors is used for prediction of preterm labour.2,5 Unfortunately, these methods are subjective, inaccurate and thus neither sensitive nor specific. As a result of incorrect clinical assessment, some of these may lead to the patient being unnecessarily hospitalised, or receiving treatment that may be detrimental or even dangerous to both mother and foetus. On the other hand some patients may have a late institution of tocolytic therapy, thus adversely affecting the success of tocolysis.
It would be desirable to have more objective methods that could accurately and rapidly identify patients at risk of preterm labour. A number of methods have been proposed - such as the evaluation of presence of cervico-vaginal foetal fibronectin,6,11 direct or indirect assessment of subclinical infection including bacterial vaginosis7 and assessment of cervical or amniotic fluid cytokine concentration.8 However, most of these techniques require expensive assays and are often unavailable in developing countries like ours.
Ultrasonographic assessment of uterine cervix has emerged as an alternate method to objectively assess cervical length and morphology for prediction of preterm labour.5,9 Use of trans-abdominal sonography is not advantageous for determination of cervical length because it requires a full bladder and is less accurate. Also, the pressure of a full bladder itself can alter the finding. Transvaginal sonography, which can provide high quality image is well accepted by patients.10
Trans-vaginal sonography can be used as a reliable and cost effective screeing procedure in both low and high risk asymptomatic patients, at risk of developing preterm labour at 23-24 week. While in symptomatic patients, it can select who are really at risk and require indoor management.
A number of studies have proved in the role of cervical assessment by sonography in prediction of preterm labour.9,10 Though, various authors have used different cut-off values of cervical length and period of gestation at which it is done, 26-30 mm of cervical length at 23-26 weeks is a more accepted practice with good sensitivity and specificity.5,9,10 Though the present study group is small in number, it confirms these findings. The predictive value can be further enhanced by calculating ‘cervical index’ as proposed by Gomez et al.5 Correlation with increased levels of foetal fibronectin can increase the predictive value of this method.6,11