Social inequalities in preterm birth in Scotland 1980-2003: findings from an area-based measure of deprivation

Objective  The preterm birth rate in Scotland has been increasing in recent years. Although preterm birth rates show a social gradient, it is unclear how this gradient has been affected by the overall increase. We examined time trends in singleton live preterm birth rates in relation to area-based socio-economic indicators.
Design  Population-based retrospective cohort study.
Setting  Scotland.
Participants  All singleton live births delivered in Scottish hospitals between 1980 and 2003 ( n = 1 423 993).
Main outcome measures  Singleton live preterm birth rates in each deprivation quintile were derived. Subgroup analyses of those born moderately preterm (32–36 weeks), very preterm (28–31 weeks) and extremely preterm (24–27 weeks) were performed.
Results  The rate of singleton live preterm births increased from 49.7 per 1000 live births in the 5-year period 1980–84 to 56.1 per 1000 in the 4-year period 2000–03, a relative increase of 12.9%. A marked social gradient was apparent at all time periods: relative indices of inequality were 1.63 (95% CI 1.38–1.92) in 1980–84 and 1.55 (1.44–1.66) in 2000–03. Similar social gradients existed for all gestational age subgroups. Smoking status at first antenatal contact and increased obstetric intervention, possibly reflecting improvements in fetal monitoring and neonatal care, appeared to explain some but not all the social gradient.
Conclusions  Social inequalities in preterm birth were apparent in Scotland between 1980 and 2003. In addition to helping pregnant women to stop smoking, other means to reduce social inequalities are required.     

Maternal height and length of gestation: Does this impact on preterm labour in Asian women?

Background: Both maternal height and ethnicity may influence the gestation length, but their independent effect is unclear.
Aim: This study was performed to examine the relationship between maternal height and gestational length in women with singleton pregnancies in a Chinese and southeast Asian population.
Methods: A retrospective cohort study was performed on women carrying singleton pregnancies with spontaneous labour in a 48-month period managed under our department to determine the relationship between maternal height, expressed in quartiles, with the mean gestational age and incidence of preterm labour.
Results: Of the 16 384 women who delivered within this period, the 25th, 50th and 75th percentile values of maternal height were 153 cm, 156 cm and 160 cm respectively. Excluded from analysis were 6597 women because of multifetal pregnancy, teenage pregnancy (maternal age ≤ 19 years old), induction of labour or elective caesarean section, or incomplete data due to no antenatal booking in our hospital. Significant differences were found in the maternal weight and body mass index, incidences of multiparity and smokers, gestational age and birthweight among the four quartiles. There was significantly increased incidence of preterm birth between 32 and 37 weeks gestation in women with shorter stature.
Conclusions: In our population, maternal height has an influence on gestational length, and the lower three quartiles was associated with increased odds of labour at > 32 to < 37 weeks. This effect should be taken into consideration in the adoption of international recommendations in obstetric management and intervention.     

Prophylactic administration of clindamycin 2 % vaginal cream to reduce the incidence of spontaneous preterm birth in women with an increased recurrence risk: a randomised placebo-controlled double-blind trial

Objective To test the hypothesis that prophylactic administration of clindamycin 2% vaginal cream can reduce the incidence of preterm birth in a high risk population.
Design A multi-centre, randomised, double-blind, placebo-controlled trial.
Setting Twelve city hospitals in The Netherlands.
Participants One hundred and sixty-eight women with a singleton pregnancy and a history of a spontaneous preterm delivery in the preceding pregnancy.
Interventions Clindamycin 2% vaginal cream, or placebo cream, administered daily for seven days at 26 and 32 weeks of gestation.
Main outcome measures Spontaneous preterm birth at c 37 weeks, admission for threatened preterm labour, neonatal infectious morbidity.
Results In the intention-to-treat analysis no difference was found in overall preterm birth between clindamycin and placebo (23% vs 18%, respectively). In the subgroup who completed the trial and administered all medication, more women delivered before 34 weeks in the clindamycin group (1.4% in the placebo vs 9.0% in the clindamycin group;   P < 0.05  ). The length of admissions for threatened preterm labour did not differ. More infectious neonatal morbidity was seen in the clindamycin group 5/83 vs 0/85;   P < 0.05  ).
Conclusion Clindamycin 2% vaginal cream given prophylactically to women with a spontaneous preterm birth in the preceding pregnancy did not prevent preterm delivery or reduce the number of admissions for threatened preterm labour. The neonatal infectious morbidity in the group treated with clindamycin was significantly higher and a major concern.     

Term breech singletons and caesarean section: A population study, Australia 1991–2005

Objective: To describe the method of birth of term breech singletons in Australia.
Design, setting and participants:  A retrospective population-based study of women who gave birth to term breech singletons in Australia between 1 January 1991 and 31 December 2005 using data from the National Perinatal Data Collection.
Main outcome measures:  Caesarean section, vaginal breech birth.
Results:  Method of birth changed for term breech singletons from 1991 (vaginal breech birth 23.1% versus caesarean (no labour 55.6%, labour 21.2%)) to 2005 (vaginal breech birth 3.7% versus caesarean (no labour 76.6%, labour 19.7%)). Overall, the population attributable risk percentage of term breech singletons for all caesarean sections declined from 10.2% in 1991 to 6.9% in 2005.
Conclusion:  Planned caesarean section is the standard method of birth for term breech singletons in Australia. Active measures including external cephalic version should be supported to reduce the rate of caesarean section where clinically indicated. Retention of a skilled clinical workforce is essential in the provision of the latter and to assist the minority of women having vaginal breech births. Breech presentation is not a major factor in the overall rise in caesarean section experienced by Australia since 1996.     

Vaginal delivery compared with caesarean section in early preterm breech delivery: a comparison of long term outcome

Objective To determine the optimum mode of delivery of the early preterm fetus in breech presentation.
Design Retrospective comparison of two cohorts of preterm breech fetus.
Setting Two tertiary care centres: at one centre the preferred management for preterm breech presentation was vaginal delivery; at the other centre, the preferred method was caesarean section.
Population All singleton infants delivered after breech presentation from 1984 through 1989, at a gestational age of 26 to 31 weeks. Those with lethal congenital abnormalities, placenta praevia, placental abruption, fetal death or fetal distress before the onset of labour were excluded.
Main outcome measures Survival without disability or handicap documented at two years corrected age. The influence of a number of relevant variables on this outcome was assessed by logistic regression analysis.
Results There was no difference in survival without disability or handicap between the centres (odds ratio 1.5, 95% CI 0.6–3.9 vaginal delivery compared with caesarean section). Survival without disability or handicap was positively influenced by increasing birthweight and corticosteroids > 24 h before birth, and negatively influenced by footling presentation.
Conclusion A policy of caesarean section for early preterm (26–31 weeks) breech delivery is not associated with increased survival without disability or handicap.     

Obstetric outcomes subsequent to intrauterine death in the first pregnancy

Objective  To compare obstetric outcomes in the pregnancy subsequent to intrauterine death with that following live birth in first pregnancy.
Design  Retrospective cohort study.
Setting  Grampian region of Scotland, UK.
Population  All women who had their first and second deliveries in Grampian between 1976 and 2006.
Methods  All women delivering for the first time between 1976 and 2002 had follow up until 2006 to study their next pregnancy. Those women who had an intrauterine death in their first pregnancy formed the exposed cohort, while those who had a live birth formed the unexposed cohort.
Main outcome measures  Maternal and neonatal outcomes in the second pregnancy, including pre-eclampsia, placental abruption, induction of labour, instrumental delivery, caesarean delivery, malpresentation, prematurity, low birthweight and stillbirth.
Results  The exposed cohort ( n = 364) was at increased risk of pre-eclampsia (OR 3.1, 95% CI 1.7–5.7); placental abruption (OR 9.4, 95% CI 4.5–19.7); induction of labour (OR 3.2, 95% CI 2.4–4.2); instrumental delivery (OR 2.0, 95% CI 1.4–3.0); elective (OR 3.1, 95% CI 2–4.8) and emergency caesarean deliveries (OR 2.1, 95% CI 1.5–3.0); and prematurity (OR 2.8, 95% CI 1.9–4.2), low birthweight (OR 2.8, 95% CI 1.7–4.5) and malpresentation (OR 2.8, 95% CI 2.0–3.9) of the infant as compared with the unexposed cohort ( n = 33 715). The adjusted odds ratio for stillbirth was 1.2 and 95% CI 0.4–3.4.
Conclusion  While the majority of women with a previous stillbirth have a live birth in the subsequent pregnancy, they are a high-risk group with an increased incidence of adverse maternal and neonatal outcomes.     

Maternal anthropometric risk factors for caesarean delivery before or after onset of labour

Objective  To quantify the effects of pre-pregnancy body mass and gestational weight gain, above and beyond their known effects on birthweight, on the risk of primary and repeat caesarean delivery performed before or after the onset of labour.
Design  Hospital-based historical cohort study.
Setting  Canadian university-affiliated hospital.
Population  A total of 63 390 singleton term (≥37 weeks gestation) infants with cephalic presentation.
Methods  We studied prospectively archived deliveries at the Royal Victoria Hospital in Montreal, Canada, from 1 January 1978 to 31 March 2001 using multiple logistic regression models to estimate relative odds of caesarean delivery.
Main outcome measure  Caesarean delivery, primary or repeat and before or after the onset of labour.
Results  Pregravid obesity (body mass index ≥30 kg/m²) increased the likelihood of primary caesarean delivery before (OR = 2.01, 95% CI 1.39–2.90) and after (OR = 2.12, 95% CI 1.86–2.42) the onset of labour. High net rate of gestational weight gain (>0.50 kg/week) increased the risk but only after labour onset (OR = 1.40, 95% CI 1.23–1.60). Among women with a previous caesarean, high weight gain modestly increased risk but only before labour (OR = 1.38, 95% CI 1.04–1.83), whereas obesity increased the risk of caesarean delivery both before (OR = 1.85, 95% CI 1.44–2.37) and after (OR = 1.96, 95% CI 1.11–3.47) labour onset. Increased risks of macrosomia accounted for the association between pregravid adiposity and repeat caesarean delivery performed after but not before the onset of labour.
Conclusions  Pregravid obesity increases the risk of caesarean delivery both before and after the onset of labour and both with and without a history of caesarean.     

The rise in singleton preterm births in the USA: the impact of labour induction

Please cite this paper as: Zhang X, Kramer M. The rise in singleton preterm births in the USA: the impact of labour induction. BJOG 2012;119:1309-1315. Objective To assess the extent to which increased rates of labour induction and caesarean section have contributed to the recent rise in preterm birth. Design National birth cohort study. Setting USA. Population and sample Singleton live births, with primary analysis based on non-Hispanic white women. Methods Ecological study based on the 50 states and the District of Columbia during two time periods 10?years apart: 1992-94 and 2002-04. Main outcome measure Preterm birth (live birth <37?completed weeks of gestation), based on an algorithm combining menstrual and clinical estimates of gestational age. Results The state-level ecological analysis among non-Hispanic white women showed that the change in preterm birth rate from 1992-94 to 2002-04 was significantly associated with the change in rate of labour induction (r?=?0.50, 95% CI 0.26-0.68), but not with the change in rate of caesarean delivery (r?=?-0.06, 95% CI -0.33 to 0.22). Weaker but otherwise similar associations with labour induction were observed in Hispanic women and in non-Hispanic black women. Conclusions Increasing use of labour induction is probably an important cause of the observed increased rate in preterm birth.     

Recurrence of preterm birth in twin pregnancies in the presence of a prior singleton preterm birth

OBJECTIVE: We examined recurrence of preterm birth in twin pregnancy in the presence of a previous singleton preterm pregnancy, and assessed if these recurrence risks differed for medically indicated and spontaneous preterm birth. METHODS: A retrospective cohort study was designed using the maternally-linked data of women who delivered a first singleton live birth followed by a twin birth in the second pregnancy (n = 2329) in Missouri (1989--97). We examined preterm birth recurrence at <37 in the second twin pregnancy among women with a prior singleton preterm birth. Recurrence risks were based on hazard ratios (HR) and 95% confidence intervals (CI) estimated from Cox proportional hazards models after adjusting for potential confounders. RESULTS: Preterm birth rates in the second twin pregnancy were 69.0% and 49.9% among women who had a previous preterm and term singleton birth, respectively (HR 1.8, 95% CI 1.6-2.1). The preterm birth rate in the second pregnancy was about 95% when the first singleton pregnancy ended at <30 weeks. Women delivering preterm following a medical intervention in the first pregnancy had increased recurrence for both spontaneous (HR 1.4, 95% CI 1.1-2.0) and indicated (HR 2.4, 95% CI 1.8-3.2) preterm birth; similarly among women with a prior spontaneous preterm birth, hazard ratios were 1.8 (95% CI 1.5-2.1) and 1.6 (95% CI 1.3-1.9), for spontaneous and indicated preterm birth in the second twin pregnancy, respectively. CONCLUSIONS: Women with a singleton preterm birth carry increased risk of preterm birth in the subsequent twin pregnancy. A history of a singleton preterm birth has an independent and additive contribution to risk of preterm birth in the subsequent twin gestation.     

Primiparity: an 'intermediate' risk group for spontaneous and medically indicated preterm birth.

OBJECTIVE: Most women in their first pregnancy are at 'unknown' risk for preterm birth. We hypothesized that such women may be at an increased risk for preterm birth in comparison to those with a prior term birth. METHODS: We used Missouri's maternally-linked data (1989-97), comprised of women delivering their first singleton live birth (N = 259 431) and women delivering their first two consecutive singleton live births (N = 154 810). We compared preterm birth (<37 weeks) rates among women with a previous term birth, women with no reproductive history (primiparous women), and in those with a previous preterm birth. Risks of spontaneous and medically indicated preterm birth were also examined after adjustments for confounders through multivariate log-binomial regression models. RESULTS: Preterm birth rates were 8.1%, 9.6%, and 23.3% among women with a previous term birth, among primiparous women, and among those with a previous preterm birth, respectively. In comparison to women with a prior term birth, risks of spontaneous preterm birth among primiparous women and among women with a prior preterm birth were 1.1-fold (95% confidence interval (CI) 1.0, 1.2) and 2.5-fold (95% CI 2.4, 2.6) higher, respectively. These risks were higher for medically indicated preterm birth among both primiparous women (RR 1.3, 95% CI 1.2, 1.4) and those with a prior preterm birth (RR 3.2, 95% CI 3.0, 3.5) than for spontaneous preterm births. CONCLUSIONS: Primiparous women are at increased risk of both medically indicated and spontaneous preterm birth. The findings suggest that studies on preterm birth should consider a risk assignment to include three groups: low-risk (prior term birth), intermediate risk (primiparity), and high-risk (prior preterm birth). This strategy will be informative for the identification of women with impending risk of delivering preterm, and complications associated with prematurity.     

A randomised controlled trial of early versus delayed oxytocin augmentation to treat primary dysfunctional labour in nulliparous women

Background  Oxytocin is widely used to speed up slow labour, especially in nulliparous women, but randomised trials, apart from one reported only in abstract, have been too small to exclude important effects.
Objective  To test the hypothesis that early use of oxytocin reduces the need for caesarean delivery.
Design  A randomised controlled trial.
Setting  Twelve obstetric units within the Northern and Yorkshire regions in the North East of England.
Participants  A total of 412 low-risk nulliparous women in spontaneous labour at term, who had been diagnosed with primary dysfunctional labour were recruited from January 1999 to December 2001.
Intervention  Immediate oxytocin administration (active group) or oxytocin withheld for up to 8 hours (conservative group).
Main outcome measures  Caesarean section and operative vaginal delivery rates. The length of labour measured from the time of randomisation to delivery. The rate of maternal Edinburgh Postnatal Depression Scale (EPDS) greater than 12 (major depression) within 48 hours of delivery.
Results  The caesarean section rates were 13.5% active versus 13.7% controls (OR 0.98, 95% CI 0.6–1.7). Operative delivery, 24.5% versus 30.9% (OR 0.73, 95% CI 0.5–1.1). The median (interquartile range) randomisation to delivery interval in the active group was 5 hours 52 minutes (3:57–8:28) and in the conservative group 9 hours 8 minutes (5:06–13:16) ( P < 0.001). The rate of EPDS >12 was 20% in the active arm versus 15% among controls (OR 1.26, 95% CI 0.7–2.2). There was one perinatal death in each group and no major differences in perinatal outcomes.
Conclusions  Among nulliparous women with primary dysfunctional labour, early use of oxytocin does not reduce caesarean section or short-term postnatal depression. However, it shortens labour considerably and may reduce operative vaginal deliveries.     

Preterm birth in a French population: the importance of births by medical decision

This analysis describes the prevalence of preterm birth by medical decision among 50,307 live births from the district of Seine-Saint-Denis in France, using a classification that distinguishes between medically decided preterm births associated with premature rupture of membranes and those for other reasons. Thirty-seven percent of singleton and 28% of twin preterm births result from labour induction or a caesarean section in the absence of labour. One-quarter of singleton indicated preterm births are associated with premature rupture of membranes. Between 28 and 31 weeks of gestation, 40% of all singleton preterm births result from a medical decision not associated with premature rupture of membranes. The high levels of indicated preterm birth must be taken into account in evaluations of preterm birth rates and trends in developed countries.     

Costing the cascade: estimating the cost of increased obstetric intervention in childbirth using population data

Objective To estimate the cost of 'the cascade' of obstetric interventions introduced during labour for low risk women.
Design A cost formula derived from population data.
Setting New South Wales, Australia.
Population All 171,157 women having a live baby during 1996 and 1997.
Methods Four groups of interventions that occur during labour were identified. A cost model was constructed using the known age-adjusted rates for low risk women having one of three birth outcomes following these pre-specified interventions. Costs were based on statewide averages for the cost of labour and birth in hospital.
Main outcome measures The outcome measure is an 'average cost unit per woman' for low risk women, predicted by the level of intervention during labour. Obstetric care is classified as either private obstetric care in a private or public hospital, or routine public hospital care.
Results The relative cost of birth increased by up to 50% for low risk primiparous women and up to 36% for low risk multiparous women as labour interventions accumulated. An epidural was associated with a sharp increase in cost of up to 32% for some primiparous low risk women, and up to 36% for some multiparous low risk women. Private obstetric care increased the overall relative cost by 9% for primiparous low risk women and 4% for multiparous low risk women.
Conclusions The initiation of a cascade of obstetric interventions during labour for low risk women is costly to the health system. Private obstetric care adds further to the cost of care for low risk women.     

Primiparity: An ‘intermediate’ risk group for spontaneous and medically indicated preterm birth

Objective.?Most women in their first pregnancy are at ‘unknown’ risk for preterm birth. We hypothesized that such women may be at an increased risk for preterm birth in comparison to those with a prior term birth.

Methods.?We used Missouri's maternally-linked data (1989–97), comprised of women delivering their first singleton live birth (N = 259 431) and women delivering their first two consecutive singleton live births (N = 154 810). We compared preterm birth (<37 weeks) rates among women with a previous term birth, women with no reproductive history (primiparous women), and in those with a previous preterm birth. Risks of spontaneous and medically indicated preterm birth were also examined after adjustments for confounders through multivariate log-binomial regression models.

Results.?Preterm birth rates were 8.1%, 9.6%, and 23.3% among women with a previous term birth, among primiparous women, and among those with a previous preterm birth, respectively. In comparison to women with a prior term birth, risks of spontaneous preterm birth among primiparous women and among women with a prior preterm birth were 1.1-fold (95% confidence interval (CI) 1.0, 1.2) and 2.5-fold (95% CI 2.4, 2.6) higher, respectively. These risks were higher for medically indicated preterm birth among both primiparous women (RR 1.3, 95% CI 1.2, 1.4) and those with a prior preterm birth (RR 3.2, 95% CI 3.0, 3.5) than for spontaneous preterm births.

Conclusions.?Primiparous women are at increased risk of both medically indicated and spontaneous preterm birth. The findings suggest that studies on preterm birth should consider a risk assignment to include three groups: low-risk (prior term birth), intermediate risk (primiparity), and high-risk (prior preterm birth). This strategy will be informative for the identification of women with impending risk of delivering preterm, and complications associated with prematurity.     

Preterm birth: the value of sonographic measurement of cervical length

Transvaginal ultrasound scanning of cervical length at approximately 20 weeks of gestation in women attending for routine antenatal care is useful for predicting the likelihood of spontaneous early preterm birth. The risk of early birth increases exponentially with decreasing cervical length in both singleton and multiple pregnancies. In such women, individualisation of risk would lead to rationalisation of antenatal care, including frequency of visits, patient education in recognising and reporting symptoms of spontaneous preterm labour and timely administration of steroids. It is also possible that in women identified as being at high risk, the rate of preterm birth might be reduced by the prophylactic use of progesterone. In women presenting with threatened spontaneous preterm labour, transvaginal measurement of cervical length provides a useful distinction between those who are likely to deliver within the subsequent 7 days and those who are not. Since only 10–20% of such women are in true spontaneous preterm labour, the cervical length measurement in rational care can avoid the current practice of hospitalisation and administration of steroids and tocolytics to all. This article reviews the evidence in support of the clinical introduction of transvaginal sonography for both the prediction and management of spontaneous preterm labour.     

Impact of metronidazole therapy on preterm birth in women with bacterial vaginosis flora (Gardnerella vaginalis): a randomised, placebo controlled trial

Objective To ascertain whether metronidazole treatment of women with a heavy growth of Gardnerella vaginalis during mid-pregnancy would reduce the risk of spontaneous preterm birth.
Design A multicentre, randomised, placebo-controlled trial
Setting Four metropolitan hospitals.
Participants Eight hundred and seventy-nine singleton women with a heavy growth of G. vaginalis or Gram stain indicative of bacterial vaginosis at 19 weeks of gestation.
Interventions Oral metronidazole (400 mg) or placebo twice daily for two days at 24 weeks of gestation, and at 29 weeks if G. vaginalis found in test-of-cure swab four weeks after treatment.
Main outcome measures Spontaneous preterm birth less than 37 weeks.
Results Intention-to-treat analysis showed no difference between metronidazole and placebo groups in overall preterm birth (31/429 [7.2%] vs 32/428 [7.5%]) or spontaneous preterm birth (20/429 [4.7%] vs 24/428 [5.6%]). Among the 480 women with bacterial vaginosis, treatment had no effect on spontaneous preterm birth (11/242 [4.5%] vs 15/238 [6.3%]). In the subset of 46 women with a previous preterm birth, women in the metronidazole group showed a significant reduction in spontaneous preterm birth (2/22 [9.1%] vs 10/24 [41.7%], OR 0.14, 95%CI 0.01–0.84). A treatment effect was also found in compliant women with a previous preterm birth and bacterial vaginosis (0/14 [0%] vs 6/17 [35.3%], OR 0.0,95%CI 0.0–0.94).
Conclusion Metronidazole treatment of women with a heavy growth of G. vaginalis or bacterial vaginosis did not reduce the preterm birth rate. Among women with a previous preterm birth, treatment reduced the risk of spontaneous preterm birth. Further studies are required to confirm these findings.     

Early versus delayed oxytocin augmentation in nulliparous women with prolonged labour—a randomised controlled trial

Objective  To study the effects of early versus delayed oxytocin augmentation on the obstetrical and neonatal outcome in nulliparous women with spontaneous but prolonged labour.
Design  Randomised controlled study.
Setting  Two delivery units in Sweden.
Population  Healthy nulliparous women with normal pregnancies, spontaneous onset of active labour, a cervical dilatation of 4–9 cm and no progress in cervical dilatation for 2 hours and for an additional hour if amniotomy was performed due to slow progress.
Methods  Women ( n = 630) were randomly allocated either to labour augmentation by oxytocin infusion (early oxytocin group) or to postponement of oxytocin augmentation for another 3 hours (expectant group).
Main outcome measure  Mode of delivery (spontaneous vaginal or instrumental vaginal delivery or caesarean section) and time from randomisation to delivery.
Results  The caesarean section rate was 29 of 314 (9%) in the early oxytocin group and 34 of 316 (11%) in the expectant group (OR 0.8, 95% CI 0.5–1.4), and instrumental vaginal delivery 54 of 314 (17%) in the early oxytocin versus 38 of 316 (12%) in the expectant group (OR 1.5, 95% CI 0.97–2.4). Early initiation of oxytocin resulted in a mean decrease of 85 minutes in the randomisation to delivery interval.
Conclusion  Early administration of oxytocin did not change the rate of caesarean section or instrumental vaginal delivery but shortened labour duration significantly in women with a 2-hour arrest in cervical dilatation. No other clear benefits or harms were seen between early and delayed administration of oxytocin.     

Evaluation of a risk scoring system as a predictor of preterm birth in an indigent population

A risk scoring system designed to predict spontaneous preterm birth was implemented in a large, indigent population as part of a multicenter trial of preterm birth prevention. A total of 7478 women with singleton gestations were screened and followed up prospectively at the Birmingham project center. Patients who had an indicated preterm delivery or a fetal anomaly were excluded from the study population. Analysis by assigned risk score and parity showed that, whereas the sensitivity and positive predictive value were better in multiparous women than in nulliparous women, overall the values were low. Logistic regression analyses of the multiparous and nulliparous populations showed independent sets of significant (p less than or equal to 0.05) risk variables. A history of preterm delivery and a low prepregnancy weight were the most predictive risk factors in the multiparous and nulliparous models, respectively. We conclude that the clinical usefulness of a risk scoring system to predict spontaneous preterm birth in an indigent population is limited.     

Trends in labour and birth interventions among low-risk women in New South Wales

OBJECTIVE: To examine recent trends in obstetric intervention rates among women at low-risk of poor pregnancy outcome. DESIGN: Cross-sectional analytic study SETTING AND POPULATION: A population of 336,189 women categorised as low-risk of a poor pregnancy outcome who gave birth to a live singleton in NSW from 1 January 1990 to 31 December 1997. MAIN OUTCOME MEASURES: Obstetric intervention rates including oxytocin induction and augmentation of labour, epidural analgesia, instrumental births, caesarean section and episiotomy METHODS: Trends over time were assessed by fitting trend-lines to numbers of births or by trends in proportions. Unconditional logistic regression was used to assess the impact of epidural analgesia on instrumental birth over time. RESULTS: Rates of operative births did not rise despite increases in maternal age and use of epidural analgesia. Instrumental births declined over time from 26% to 22% among primiparas and 5% to 4% among multiparas. There was also a shift to vacuum extraction rather than forceps. Although instrumental birth was strongly associated with epidural analgesia, the strength of the association declined over the study period, for primiparas from an adjusted odds ratio of 7.2 to 5.2 and for multiparas from 13.2 to 10.3. CONCLUSIONS: Increased use of epidural analgesia for labour has been a feature of the management of birth at term during the 1990s. The decline in the strength of association between epidural analgesia and instrumental birth may reflect improved epidural techniques and management of epidural labour, and recognition of the adverse maternal outcomes associated with forceps and vacuum births.