Did preterm deliveries continue to decrease in France in the 1980s?

Stillbirth and preterm birth and associated factors in one of the largest cities in central Vietnam

AIM

Little is known about the rate of stillbirths, preterm births and associated risk factors in resource-limited settings like Vietnam. This study reports those rates for Da Nang, which is one of the largest cities in central Vietnam.

METHODS

Data on 20 762 births including stillbirths and preterm births and associated risk factors were prospectively collected from health facilities from April 2015 to March 2016.

RESULTS

The data represented 85% of the total births in Da Nang during the study period, and a stillbirth rate of 9.7 per 1000 live births was recorded. The preterm rate for live births was just under 5%. Independent factors associated with an increased risk of stillbirth and preterm births were mothers aged 35 plus, working as farmers, living in the provinces and a history of abortion. Mothers under 20 years with previous preterm births faced a higher risk of another preterm birth.

CONCLUSION

The stillbirth and premature birth rates in Da Nang were higher than rates in high-income countries. Developing registration programmes in Vietnam will provide improved data that will enable researchers and policymakers to identify strategies to reduce the number of stillbirths and premature births.

Preterm birth: Case definition & guidelines for data collection, analysis, and presentation of immunisation safety data

Preterm birth is commonly defined as any birth before 37 weeks completed weeks of gestation. An estimated 15 million infants are born preterm globally, disproportionately affecting low and middle income countries (LMIC). It contributes directly to estimated one million neonatal deaths annually and is a significant contributor to childhood morbidity. However, in many clinical settings, the information available to calculate completed weeks of gestation varies widely. Accurate dating of the last menstrual period (LMP), as well as access to clinical and ultrasonographic evaluation are important components of gestational age assessment antenatally. This case definition assign levels of confidence to categorisation of births as preterm, utilising assessment modalities which may be available across different settings. These are designed to enable systematic safety evaluation of vaccine clinical trials and post-implementation programmes of immunisations in pregnancy.

Characteristics of childbearing women, obstetrical interventions and preterm delivery: a comparison of the US and France

Preterm delivery rates have remained consistently higher in the US than France, but the reasons for this excess remain poorly understood. We examined if differences in socio-demographic risk factors or more liberal use of obstetrical interventions contributed to higher rates in the US. Data on singleton live births in 1995, 1998 and 2003 from US birth certificates and the French National Perinatal Survey were used to analyze preterm delivery rate by maternal characteristics (age, parity, marital status, education, race (US)/nationality (France), prenatal care and smoking). We distinguished between preterm deliveries with a cesarean or a labor induction and those without these interventions. Unadjusted and adjusted risk ratios (RR) for the US compared to France were estimated using log-binomial regression. Preterm delivery rates were 7.9 % in the US and 4.7 % in France (risk ratio [RR] = 1.7, 95 % confidence interval [CI] 1.6-1.8). The US had more teen mothers and late entry to prenatal care, but fewer women smoked, although adjustment for these and other confounders did not reduce RR (1.8, 95 % CI 1.7-1.9). Preterm delivery rates associated with labor induction or cesarean were 3.3 % in the US and 2.1 % in France (RR 1.6, 95 % CI 1.5-1.7); the corresponding rates for preterm delivery without these interventions were 4.5 and 2.5 % (RR 1.8, 95 % CI 1.7-1.9), respectively. Key socio-demographic risk factors and more obstetric intervention do not explain higher US preterm delivery rates. Avenues for future research include the impact of universal access to health services (universal health insurance?) on health care quality and the association between more generous social policies, stress and the risks of preterm delivery.

Nutritional modulation of the gut microbiota and immune system in preterm neonates susceptible to necrotizing enterocolitis

The gastrointestinal inflammatory disorder, necrotizing enterocolitis (NEC), is among the most serious diseases for preterm neonates. Nutritional, microbiological and immunological dysfunctions all play a role in disease progression but the relationship among these determinants is not understood. The preterm gut is very sensitive to enteral feeding which may either promote gut adaptation and health, or induce gut dysfunction, bacterial overgrowth and inflammation. Uncontrolled inflammatory reactions may be initiated by maldigestion and impaired mucosal protection, leading to bacterial overgrowth and excessive nutrient fermentation. Tumor necrosis factor alpha, toll-like receptors and heat-shock proteins are identified among the immunological components of the early mucosal dysfunction. It remains difficult, however, to distinguish the early initiators of NEC from the later consequences of the disease pathology. To elucidate the mechanisms and identify clinical interventions, animal models showing spontaneous NEC development after preterm birth coupled with different forms of feeding may help. In this review, we summarize the literature and some recent results from studies on preterm pigs on the nutritional, microbial and immunological interactions during the early feeding-induced mucosal dysfunction and later NEC development. We show that introduction of suboptimal enteral formula diets, coupled with parenteral nutrition, predispose to disease, while advancing amounts of mother's milk from birth (particularly colostrum) protects against disease. Hence, the transition from parenteral to enteral nutrition shortly after birth plays a pivotal role to secure gut growth, digestive maturation and an appropriate response to bacterial colonization in the sensitive gut of preterm neonates.

Repeat digital cervical assessment in pregnancy for identifying women at risk of preterm labour

BACKGROUND

Repeat digital cervical assessment (RDCA - examination of the cervix with a finger) has been promoted as a routine intervention in the antenatal clinic as a screening test for the risk of preterm birth (that is, birth occurring before 37 weeks of gestation).

OBJECTIVES

To assess the effect of repeat digital cervical assessment during pregnancy for the risk of preterm birth and other adverse effects for mother and baby.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (September 2009) and CENTRAL (The Cochrane Library 2009, Issue 3).

SELECTION CRITERIA

All known randomized clinical trials comparing repeat digital cervical assessment with internal examination limited to clinical indication or no internal examination. We have not included studies where repeat cervical assessment is only a component of complex interventions targeted at decreasing preterm birth.

DATA COLLECTION AND ANALYSIS

We evaluated relevant studies for meeting the inclusion criteria and methodological quality without considering their results. Three review authors extracted the data. For all data analyses, we entered data based on the principle of intention to treat. We calculated odds ratios and 95% confidence intervals for dichotomous data.

MAIN RESULTS

We included two trials that enrolled a total of 7163 women. Preterm birth before 37 weeks, was reported in both trials. The odds ratio for birth before 37 weeks was 1.05 (95% confidence interval 0.85 to 1.31; two trials, 6070 women). One trial (involving 5836 women) found no significant difference between the two treatment arms for the following outcomes: preterm birth before 34 weeks; preterm, prelabour rupture of membranes; hospital admission before 37 weeks; caesarean section; use of tocolytic drugs; low birthweight; very low birthweight, stillbirth, neonatal death, neonatal intensive care admissions; use of health services. The other prespecified outcomes were not evaluated in the included studies. We did not conduct the planned subgroup analyses due to insufficient data.

AUTHORS' CONCLUSIONS

We found no evidence to support the use of RDCA in pregnancy to reduce the prevalence of preterm birth. We have found insufficient evidence to assess adverse effects of the intervention.

Global report on preterm birth and stillbirth (1 of 7): definitions, description of the burden and opportunities to improve data

INTRODUCTION

This is the first of seven articles from a preterm birth and stillbirth report. Presented here is an overview of the burden, an assessment of the quality of current estimates, review of trends, and recommendations to improve data.

PRETERM BIRTH

Few countries have reliable national preterm birth prevalence data. Globally, an estimated 13 million babies are born before 37 completed weeks of gestation annually. Rates are generally highest in low- and middle-income countries, and increasing in some middle- and high-income countries, particularly the Americas. Preterm birth is the leading direct cause of neonatal death (27%); more than one million preterm newborns die annually. Preterm birth is also the dominant risk factor for neonatal mortality, particularly for deaths due to infections. Long-term impairment is an increasing issue.

STILLBIRTH

Stillbirths are currently not included in Millennium Development Goal tracking and remain invisible in global policies. For international comparisons, stillbirths include late fetal deaths weighing more than 1000g or occurring after 28 weeks gestation. Only about 2% of all stillbirths are counted through vital registration and global estimates are based on household surveys or modelling. Two global estimation exercises reached a similar estimate of around three million annually; 99% occur in low- and middle-income countries. One million stillbirths occur during birth. Global stillbirth cause-of-death estimates are impeded by multiple, complex classification systems.

RECOMMENDATIONS TO IMPROVE DATA

(1) increase the capture and quality of pregnancy outcome data through household surveys, the main data source for countries with 75% of the global burden; (2) increase compliance with standard definitions of gestational age and stillbirth in routine data collection systems; (3) strengthen existing data collection mechanisms--especially vital registration and facility data--by instituting a standard death certificate for stillbirth and neonatal death linked to revised International Classification of Diseases coding; (4) validate a simple, standardized classification system for stillbirth cause-of-death; and (5) improve systems and tools to capture acute morbidity and long-term impairment outcomes following preterm birth.

CONCLUSION

Lack of adequate data hampers visibility, effective policies, and research. Immediate opportunities exist to improve data tracking and reduce the burden of preterm birth and stillbirth.

Medically indicated preterm birth: recognizing the importance of the problem

Preterm birth complicates over 500,000 births annually, affecting 12.5% of pregnancies in the United States. Much of the temporal increase in preterm birth (<37 weeks) over the past decade is largely driven by a concurrent temporal increase in medically indicated preterm birth. Maternal and fetal indications that prompt an intervention at preterm gestational ages include preeclampsia, intrauterine growth restriction, and placental abruption-conditions that constitute "ischemic placental disease." Ischemic placental disease is implicated in over one of every two indicated preterm births compared with less than one in five births at term. Comprehensive evaluation of risk factors, with careful consideration of heterogeneity in the syndrome of medically indicated preterm birth and ischemic placental disease may provide important clues to predict and consequently prevent preterm birth.

Epidemiology of preterm birth and its clinical subtypes

Preterm birth (<37 weeks) complicates 12.5% of all deliveries in the USA, and remains the leading cause of perinatal mortality and morbidity, accounting for as many as 75% of perinatal deaths. Despite the recent temporal increase in preterm birth, efforts to understand the problem of prematurity have met with little success. This may be attributable to the under-appreciation of the etiologic heterogeneity of preterm birth as well as the heterogeneity in its underlying clinical presentations--spontaneous onset of labor, preterm premature rupture of membranes, and medically indicated preterm birth. In this paper, we review data regarding preterm births with particular focus on its incidence, temporal trends, and recurrence. Studies of births from the USA indicate that the recent temporal increase in the overall preterm birth rate is driven by an impressive concomitant increase in medically indicated preterm birth. However, the largest temporal decline in perinatal mortality has also occurred among medically indicated preterm births (relative to other clinical subtypes), suggesting that these obstetric interventions at preterm gestational ages are associated with a reduction in perinatal mortality. Recent data indicate that spontaneous preterm birth is not only associated with increased recurrence of spontaneous, but also medically indicated, preterm birth, and vice versa. This suggests that the clinical subtypes may share common underlying etiologies. Since medically indicated preterm birth accounts for as many as 40% of all preterm births, efforts to understand the reasons for such interventions and their impact on short- and long-term morbidity in newborns is compelling. Further research is necessary in order to understand the mechanisms and etiology of preterm birth, thus leading to the possibility of effective preventive or therapeutic strategies.

Theory of obstetrics: an epidemiologic framework for justifying medically indicated early delivery

BACKGROUND

Modern obstetrics is faced with a serious paradox. Obstetric practice is becoming increasingly interventionist based on empirical evidence but without a theoretical basis for such intervention. Whereas obstetric models of perinatal death show that mortality declines exponentially with increasing gestational duration, temporal increases in medically indicated labour induction and cesarean delivery have resulted in rising rates of preterm birth and declining rates of postterm birth. Other problems include a disconnection between patterns of gestational age-specific growth restriction (constant across gestation) and gestational age-specific perinatal mortality (exponential decline with increasing duration) and the paradox of intersecting perinatal mortality curves (low birth weight infants of smokers have lower neonatal mortality rates than the low birth weight infants of non-smokers).

DISCUSSION

The fetuses at risk approach is a causal model that brings coherence to the various perinatal phenomena. Under this formulation, pregnancy complications (such as preeclampsia), labour induction/cesarean delivery, birth, revealed small-for-gestational age and death show coherent patterns of incidence. The fetuses at risk formulation also provides a theoretical justification for medically indicated early delivery, the cornerstone of modern obstetrics. It permits a conceptualization of the number needed to treat (e.g., as low as 2 for emergency cesarean delivery in preventing perinatal death given placental abruption and fetal bradycardia) and a calculation of the marginal number needed to treat (i.e., the number of additional medically indicated labour inductions/cesarean deliveries required to prevent one perinatal death). Data from the United States showed that between 1995-96 and 1999-2000 rates of labour induction/cesarean delivery increased by 45.1 per 1,000 and perinatal mortality decreased by 0.31 per 1,000 total births among singleton pregnancies at > or = 28 weeks of gestation. The marginal number needed to treat was 145 (45.1/0.31), showing that 145 excess labour inductions/cesarean deliveries in 1999-2000 (relative to 1995-96) were responsible for preventing 1 perinatal death among singleton pregnancies at > or = 28 weeks gestation.

SUMMARY

The fetuses at risk approach, with its focus on incidence measures, provides a coherent view of perinatal phenomena. It also provides a theoretical justification for medically indicated early delivery and reconciles the contemporary divide between obstetric theory and obstetric practice.

Fetal growth and onset of delivery: a nationwide population-based study of preterm infants

OBJECTIVE

This study was undertaken to assess whether deviations from normal fetal growth are associated with spontaneous preterm delivery.

STUDY DESIGN

A population-based study was performed, using Swedish Medical Birth Register data from 1991 through 2001. The total population comprised 1,007,648 singleton births. Intrauterine-derived growth standards were used to identify individual standard deviation (SD) from expected birth weight. Spontaneous preterm infants were compared with infants born after spontaneous labor at term. Results were obtained by using multiple logistic regression analysis.

RESULTS

Associations between smaller than population mean and spontaneous preterm birth were evident for all gestational age groups. The largest risk was found at 28 to 31 gestational weeks and birth weight less than -3 SD (OR: 13.3; 95% CI: 10.3-17.2). Spontaneous preterm infants born at 34 to 36 gestational weeks weighed 1 to 1.9 SD (OR: 1.1; 95% CI: 1.1-1.2) or 2 to 2.9 SD (OR: 1.6; 95% CI: 1.5-1.7) above the expected mean more often.

CONCLUSION

Deviation of fetal growth from the expected mean is associated with spontaneous preterm delivery.

Trends in twin preterm birth subtypes in the United States, 1989 through 2000: impact on perinatal mortality

OBJECTIVE

We examined trends in twin preterm birth <37 weeks following ruptured membranes (ROM), medically indicated preterm birth, and preterm birth following spontaneous onset of labor (PTL). We further examined whether the changes in preterm birth subtypes were associated with trends in twin perinatal mortality.

STUDY DESIGN

We carried out a retrospective cohort study of 1,172,405 twin live births and stillbirths delivered in the US between 1989 and 2000. Trends in preterm birth subtypes and perinatal mortality (stillbirths at > or = 22 weeks plus neonatal deaths within 28 days) were examined through ecological logistic regression models after adjusting for confounders.

RESULTS

Twin preterm birth among whites increased from 46.6% in 1989 to 1990 to 56.7% in 1999 to 2000, and from 56.1% to 61.0% among blacks over the same period. Medically indicated preterm birth increased by 50% (95% CI 49-52) among whites, and by 33% (95% CI 29-36) among blacks. PTL increased by 24% among whites, but remained fairly unchanged among blacks between the two periods. Preterm birth following ROM also did not change between the 2 periods among whites, but declined by 7% among blacks. Perinatal mortality among twin births declined by 41% (95% CI 38-44) among whites, and by 37% (95% CI 32-42) among blacks between 1989 and 1990 and 1999 and 2000. This mortality decline was most closely associated with the increase in medically indicated preterm birth among whites, and with the decrease in preterm birth following ROM among blacks.

CONCLUSION

Temporal trends in twin preterm birth varied substantially based on underlying subtypes and race. The increase in medically indicated preterm birth is associated with a large reduction in perinatal mortality.

Primary predictors of preterm labour

Spontaneous preterm birth accounts for 60% of all preterm births in developed countries. With the increase in multiple pregnancies, induced preterm birth and the progress in neonatal care for extremely preterm neonates, spontaneous preterm birth for singleton pregnancies in developed countries has probably decreased over the past 30 years. This decrease is likely to be related to better prenatal care for all pregnant women because the recognition of primary risk factors in early or late pregnancy remains a basic part of prenatal care. The failure to distinguish between induced and spontaneous preterm labour in most population-based studies makes it difficult to interpret results with respect to the primary predictors of preterm labour. Many such primary predictors of preterm labour have been used over the past 20-30 years. These include individual factors, socio-economic factors, working conditions and obstetric and gynaecological history. Risk scores have been proposed in order to produce these data. Unfortunately, the predictive value of these scores, especially their specificity, is poor, mainly because all of these factors are indirect. We still cannot identify the mechanisms that lead to preterm labour and birth. New markers more directly related to preterm labour have recently been proposed, some of which relate to direct causes of preterm labour such as cervical ultrasound measurement, fetal fibronectin (FFN), salivary estriol, serum CRH and bacterial vaginosis. Several of these have predictive values, which are potentially useful for clinical practice. Nonetheless, pregnant women in developed countries are already closely monitored throughout pregnancy. Before proposing new screening tests to be applied systematically to all pregnant women, their advantages and drawbacks must be fully evaluated.

Indicators of fetal and infant health outcomes

OBJECTIVE

To assess the ability of the member states of the European Union to produce the indicators recommended by the PERISTAT project on perinatal health indicators and to provide an overview of fetal and infant health outcomes for these countries according to the information now available.

METHODS

We used data from the PERISTAT survey of data providers to compute PERISTAT indicators of fetal and infant health.

RESULTS

National data on fetal mortality are available for all countries, but vary in their definitions. To adjust for these differences in definition, PERISTAT recommends presenting rates by gestational age and birth weight. Not all countries can provide neonatal mortality data by gestational age, birth weight or plurality, as recommended by PERISTAT. Few countries in Europe can report infant mortality rates by birth weight and gestational age. The other recommended indicators are available to varying degrees.

CONCLUSIONS

This overview, which shows that Europe can produce a variety of indicators for monitoring the health of its new-borns, indicates that some key dimensions of perinatal health cannot now be measured with routine health statistics and reveals important disparities in health outcomes throughout Europe. For most indicators, the highest values are between 50 and 100% higher than the lowest values. The reasons for these variations and their importance for the surveillance of perinatal health are discussed.

Delivery of singleton preterm infants in New South Wales, 1990-1997

OBJECTIVE

To examine trends in the maternal characteristics and delivery of singleton preterm infants in an Australian population.

DESIGN

Population-based descriptive study.

SETTING

New South Wales (NSW), Australia.

POPULATION

The population included 37 500 singleton preterm births from 1 January 1990 to 31 December 1997.

METHODS

Data were obtained from the NSW Midwives' Data Collection (MDC) and rates over time were calculated. Preterm birth by Caesarean section before the onset of labour or where labour was induced were considered to be medically indicated.

MAIN OUTCOME MEASURES

Preterm rates, medically indicated preterm birth rates, mode of delivery andneonatal outcomes, and trends over time.

RESULTS

Among singleton infants, there was no significant change over time in the rate of preterm birth (annual average 5.5%), preterm births that were medically indicated (annual average 29.3%) or neonatal outcomes of preterm births. The rate of indicated preterm birth varied by gestational age and was highest (39.7%) at 29-32 weeks' gestation. Instrumental preterm births declined over time from 9.5 to 7.8% with a shift from forceps to vacuum use and episiotomy rates declined from 19.7 to 14.8%.

CONCLUSIONS

Increases in the reported overall preterm rate (singletons and multiples) were not due to increased delivery of singleton infants. Changes in the management of singleton preterm births were similar to changes observed in term births such as decreasing forceps and episiotomy usage. It may be to time to reassess whether Australian clinicians would be willing to randomise patients to clinical trials of the best method of delivery for preterm infants.

Obstetric intervention, stillbirth, and preterm birth

Despite widespread recognition that preventing preterm birth is the most important perinatal challenge facing industrialized countries, preterm birth has increased steadily in recent years. This article examines the relation between trends in preterm birth, preterm labor induction/cesarean delivery, stillbirth, and infant mortality. The recent rise in preterm birth in the United States and Canada has been mainly due to increases in mild preterm birth (34-36 weeks). Live births at 34 to 36 weeks' gestation have increased largely as a consequence of increases in preterm induction and preterm cesarean delivery among women at high risk for adverse pregnancy outcomes. Increased obstetric intervention at 34 to 36 weeks' gestation appears to have led to larger-than-expected temporal declines in stillbirth rates at this gestation. Infant mortality rates have declined overall and also among live births at 34 to 36 weeks' gestation. Obstetric intervention at preterm gestation, when indicated, can prevent stillbirth and reduce infant morbidity and mortality despite the increasing rates of preterm delivery.

Trends in the occurrence, determinants, and consequences of multiple births

After a substantial decrease in the middle of the 20th century, multiple pregnancy rates have increased in many Western countries. Between the mid-1970s and 1998, the rate of twin pregnancies increased by 50% to 60% in England and Wales, France, and the United States. The rates of triplet or higher-order multiple pregnancies increased by 310% in France, 430% in England and Wales, and 696% in the United States. One fourth to one third of the increase in twin or triplet pregnancies are attributable to a contemporaneous increase in maternal age. Furthermore, in countries with high occurrence of multiple births, 30% to 50% of twin pregnancies and at least 75% of triplet pregnancies occur after infertility treatment. The impact of the increase in multiple births on preterm delivery rates in the overall population is mainly attributable to twin pregnancies. In Canada, France, and the United States, an increase in preterm births among multiples contributed almost as much as the increase in occurrence of multiple births to the increase or stabilization of the overall rates of preterm delivery observed in these countries.

Socioeconomic status and preterm birth: New Zealand trends, 1980 to 1999

BACKGROUND

While a number of countries have reported rising preterm birth rates over the past two decades, none has examined the effects of socioeconomic status on preterm birth at a national level.

AIM

To document the changing incidence of preterm birth in New Zealand over the past 20 years and to determine whether particular socioeconomic or ethnic subsections of the population have contributed disproportionately to the changes seen.

METHODS

Birth registration data routinely available from the New Zealand Health Information Service were analysed for the period 1980-99. Information for a total of 1 079 478 singleton live births was linked by Domicile Code to the New Zealand Deprivation Index, a small area index of deprivation.

RESULTS

Singleton preterm birth rates rose by 37.2% during the 20 year period, from 4.3% in 1980 to 5.9% in 1999. Rates increased by 71.9% among those living in the most affluent areas, but by only 3.5% among those living in the most deprived areas, resulting in the disappearance of a socioeconomic gradient in preterm birth that had existed during the early 1980s.

CONCLUSIONS

This study challenges traditional thinking on the associations between socioeconomic status and preterm birth. Further research is necessary if the changes that have occurred in New Zealand over the past 20 years are to be fully understood.

Marital status, cohabitation, and risk of preterm birth in Europe: where births outside marriage are common and uncommon

This article explores whether the impact of marital status on the risk of preterm birth varies in relation to marital practices in the population, defined by the proportion of out-of-marriage births. Data come from a case-control study of the determinants of preterm birth in 16 European countries (5456 cases and 8234 controls). There is a significantly elevated risk of preterm birth associated with both cohabitation (OR = 1.29 [1.08, 1.55]) and single motherhood (OR = 1.61 [1.26, 2.07]) for women living in countries where fewer than 20 of births occur outside marriage. In contrast, there is no excess risk associated with marital status when out-of-marriage births are more common. This overall result does not apply to all subgroups of preterm births: different patterns emerge for early preterm births and preterm births induced for medical reasons. It is important to consider social context in the analysis of individual risk factors.

Transvaginal sonographic cervical length changes during normal pregnancy

OBJECTIVE

To examine the relationship between cervical length and gestational age in normal pregnancy in nulliparous versus parous women.

METHODS

We studied a cross-sectional sample of 321 pregnant women, including 185 nulliparous and 136 multiparous women. The inclusion criteria were sonographic confirmation of gestational age within the 12th week, the absence of any risk factors for preterm birth, and uncomplicated pregnancy with expected delivery during the 38th to 42nd weeks. Cervical length was measured in a straight line if the cervix did not show any curvature; in the presence of cervical curvature, the measurement was broken down into 2 or more segments.

RESULTS

There was a relationship between gestational age and cervical length, which could be described with a linear function (R = 0.92; R2 = 0.85; P < .001). Moreover, there was no statistically significant difference between multiparous and nulliparous women.

CONCLUSIONS

Our study shows that cervical length is comparable in nulliparous and multiparous women throughout pregnancy. In both groups, it actually shows a progressive, linear reduction between the 10th and 40th weeks. Reference ranges constructed for the whole gestational period might be more useful than a single cut-off value for more efficient prevention and management of preterm birth.

How does early ultrasound scan estimation of gestational age lead to higher rates of preterm birth?

OBJECTIVE

Early ultrasound scanning estimation of gestational age is known to increase the reported preterm delivery rate (<37 completed weeks) compared with estimation by date of the last normal menstrual period, but it is unclear how this systematic difference arises.

STUDY DESIGN

This study was a hospital-based study of 44,623 women who delivered a live-born or stillborn infant between January 1, 1978, and March 31, 1996, and who had both last normal menstrual period-based and early (usually at 16-18 weeks) ultrasound scan-based gestational age estimates. Cross-classification of the 2 estimates by completed weeks was used to examine the direction and magnitude of the differences between them and to compare the resulting classifications of preterm birth.

RESULTS

The early ultrasound scan-based gestational age distribution was shifted uniformly to the left (ie, lower gestational age) relative to the last normal menstrual period gestational age distribution; the early ultrasound scan-based preterm delivery rate was 9.1%, which was 19.5% (n = 659 births) higher than the 7.6% rate by last normal menstrual period (P <.0001). The last normal menstrual period estimate exceeded the early ultrasound scan estimate far more often than the reverse, up to and including early ultrasound scan estimates of 40 weeks. No concentration of 4-week discrepancies was observed in either direction, as would be expected with random or systematic errors in recall of the last normal menstrual period. The absolute number of births at 37 to 39 weeks of gestation (by last normal menstrual period) that were reclassified as preterm (n = 1206 births) was much higher than the number of preterm births at 34 to 36 weeks of gestation that were reclassified as term (n = 581 births). The net increase of 625 preterm births (from 581 to 1206 births) that resulted from reclassification of births at 37 to 39 last normal menstrual period weeks accounted for 95% of the total 659-birth increase in early ultrasound scan-based preterm births at all last normal menstrual period gestational ages.

CONCLUSION

Early ultrasound scanning reduces the gestational age estimate across the entire gestational age range; early ultrasound scan-based reclassification of gestational age results in a substantial increase in the prevalence of preterm births. Small downward reclassifications exceed upward reclassifications of similar magnitude, which is consistent with previous reports that delayed (>14 days) ovulation is more frequent than early (<14 days) ovulation.

The epidemiology of preterm labor

There are many factors that are associated with preterm labor and delivery. These include maternal conditions such as medical illness, anemia and uterine malformation. They may be related to past events such as prior obstetric complication, previous preterm labor, cervical surgery or induced abortion. They may be intrinsic to the current pregnancy, such as reproductive tract infection, multifetal gestation, maternal age, short interpregnancy interval or prolonged menstrual conception interval. Maternal behaviors such as smoking and substance abuse can be risk factors for a short gestation. Demographic variables such as race, employment and socioeconomic status can also be associated with preterm labor. This article briefly reviews these subjects.

Maternal age, social changes, and pregnancy outcome in Ribeirão Preto, southeast Brazil, in 1978-79 and 1994

This study focused on changes in demographic, social, and health-care patterns and pregnancy outcome related to maternal age from 1978-79 to 1994 in Ribeirão Preto, São Paulo State, Brazil. Information on pregnancy outcome was obtained from two cohorts of singleton live births, 6,681 births in 1978/79 and 2,839 births in 1994. A standardized questionnaire was submitted to mothers after delivery, and demographic information was collected from official records. There was a significant increase in teenage pregnancies (from 5.1% to 7.4%) and a decrease in infant mortality (36/1,000 to 17/1,000). There were significant decreases in the proportion of mothers with low schooling (24.5% to 14.4%), smoking (28.9% to 21.%), and multiparity (14.7% to 9.0%). Prenatal coverage improved (from 23.4% to 9.0% of patients with fewer than 4 prenatal visits), while cesareans increased (from 30.6% to 50.8%), as did preterm delivery (7.2% to 13.6%) and low birthweight (7.2% to 10.6%). Despite significant improvements in some maternal characteristics, the proportion of teenage pregnancies, preterm deliveries, low birthweight, and cesareans increased, raising concerns about the health costs and consequences for mothers and infants.

The relationship between intrauterine growth restriction and preterm delivery: an empirical approach using data from a European case-control study

OBJECTIVE

To test whether being small for gestational age, defined as having a birthweight less than the 10th centile of intrauterine growth references, is a risk factor for preterm delivery for singleton live births.

DESIGN

A case-control study.

SETTING

Maternity hospitals in 16 European countries.

SAMPLE

Four thousand and seven hundred preterm infants between 22 and 36 completed weeks of gestation and 6,460 control infants between 37 and 40 weeks of gestation.

METHODS

Newborn babies are identified as being small for gestational age using customized reference standards derived from models of fetal growth. The impact of being small for gestational age on preterm delivery is estimated using logistic regression.

MAIN OUTCOME MEASURE

Spontaneous or induced preterm delivery.

RESULTS

Being small for gestational age is significantly associated with preterm birth, although the magnitude of this association differs greatly by type of delivery and gestational age. Over 40% of induced preterm births for reasons other than the premature rupture of membranes are small for gestational age compared with 10.7% of control infants (OR 6.41). For spontaneous or premature rupture of membranes related preterm births, the association is also significant, but weaker (OR 1.51). The relationship between growth restriction and preterm delivery is strongest for preterm births before 34 weeks of gestation.

CONCLUSIONS

These findings highlight the phenomenon of abnormal fetal growth in all premature infants and, in particular, infants delivered by medical decision for reasons other than premature rupture of membranes. The observed association between being small for gestational age and preterm delivery among spontaneous preterm births merits further attention because the causal mechanisms are not well understood.

Factors associated with preterm births in southeast Brazil: a comparison of two birth cohorts born 15 years apart

An increase in preterm deliveries in Ribeirão Preto stimulated an analysis of possible explanatory factors. Two cohorts of singleton livebirths were studied, the first based on 6746 births in 1978-9 and the second based on 2846 births in 1994. A logistic regression was carried out to assess the association of preterm birth with several sociodemographic, behavioural and clinical variables, including year of survey. Delivery in private settings compared with a public setting, maternal age of < or = 17 compared with any other age group, and mothers who had had previous abortions and previous stillbirths were associated with greater rates of preterm birth. Although there was an increase in preterm birth rates regardless of mode of delivery, the increase was greater in the caesarean section group than in the vaginal delivery group. Over the study period, deliveries in private hospitals and caesarean section operations increased markedly (from 4% to 36% and from 30% to 51% respectively). Caesarean section may be the main contributor to the increase of preterm birth rate in this study. It is essential to ensure that health-care staff, especially those in private facilities, are properly educated and audited.

Fetal growth retardation: a limit for the further reduction of preterm births

Fetal growth retardation is at present the major obstacle for further reduction in preterm births. After 25 years of continuous decline in the preterm birth rate in France from 6.9% in 1972 to 4.4% in 1981 and 3.8% in 1989, there has been an increase to 4.5% in 1995. The major new fact is the progressive increase of medically induced preterm births, mostly related to fetal growth retardation. Spontaneous preterm births have continued to decrease throughout all these years.

Determinants of preterm birth rates in Canada from 1981 through 1983 and from 1992 through 1994

BACKGROUND

The rates of preterm birth have increased in many countries, including Canada, over the past 20 years. However, the factors underlying the increase are poorly understood.

METHODS

We used data from the Statistics Canada live-birth and stillbirth data bases to determine the effects of changes in the frequency of multiple births, registration of births occurring very early in gestation, patterns of obstetrical intervention, and use of ultrasonographic dating of gestational age on the rates of preterm birth in Canada from 1981 through 1983 and from 1992 through 1994. All births in 9 of the 12 provinces and territories of Canada were included. Logistic-regression analysis and Poisson regression analysis were used to estimate changes between the two three-year periods, after adjustment for the above-mentioned determinants of the likelihood of preterm births.

RESULTS

Preterm births increased from 6.3 percent of live births in 1981 through 1983 to 6.8 percent in 1992 through 1994, a relative increase of 9 percent (95 percent confidence interval, 7 to 10 percent). Among singleton births, preterm births increased by 5 percent (95 percent confidence interval, 3 to 6 percent). Multiple births increased from 1.9 percent to 2.1 percent of all live births; the rates of preterm birth among live births resulting from multiple gestations increased by 25 percent (95 percent confidence interval, 21 to 28 percent). Adjustment for the determinants of the likelihood of preterm birth reduced the increase in the rate of preterm birth to 3 percent among all live births and 1 percent among singleton births.

CONCLUSIONS

The recent increase in preterm births in Canada is largely attributable to changes in the frequency of multiple births, obstetrical intervention, and the use of ultrasound-based estimates of gestational age.

The preterm prediction study: risk factors for indicated preterm births. Maternal-Fetal Medicine Units Network of the National Institute of Child Health and Human Development

OBJECTIVE

Preterm births occur for many different reasons. Most efforts to identify risk factors for preterm births either ignore cause and consider preterm births as a single entity or examine risk factors for spontaneous preterm births. We performed this study to examine risk factors for indicated preterm births, which constitute more than one quarter of all preterm births.

STUDY DESIGN

The study included 2929 women evaluated at 24 weeks' gestation at 10 centers. Information was gathered about demographic factors, socioeconomic status, home and work environments, drug and alcohol use, and medical history. In addition vaginal samples were evaluated for fetal fibronectin and bacterial vaginosis and cervical length was measured by transvaginal ultrasonography. Associations with indicated preterm birth were evaluated by univariate tests and by multivariable analysis with logistic regression.

RESULTS

Of the women studied at 24 weeks' gestation 15.3% were delivered of their infants at <37 weeks' gestation. Of these deliveries, 27.7% were indicated preterm births. Risk factors in the final multivariable model were, in order of decreasing odds ratios, mullerian duct abnormality (odds ratio 7.02), proteinuria at <24 weeks' gestation (odds ratio 5.85), history of chronic hypertension (odds ratio 4.06), history of previous indicated preterm birth (odds ratio 2.79), history of lung disease (odds ratio 2.52), previous spontaneous preterm birth (odds ratio 2.45), age >30 years (odds ratio 2.42), black ethnicity (odds ratio 1.56), and working during pregnancy (odds ratio 1.49). Alcohol use in pregnancy was actually associated with a lower risk of indicated preterm birth (odds ratio 0.35).

CONCLUSION

The risk factors found in this analysis tend to be different from those associated with spontaneous preterm birth.

Are sociodemographic factors predictive of preterm birth? A reappraisal of the 1958 British Perinatal Mortality Survey

OBJECTIVE

Reassessment of the predictive value of sociodemographic factors on preterm birth.

DESIGN

Population-based case-control study.

SETTING

England, Wales and Scotland.

SAMPLE

The study sample consisted of 5630 primiparous and 9538 multiparous women who were delivered during the first week of March 1958 in Britain. Multiple births were excluded.

METHOD

Factors potentially predictive of preterm birth were assessed for primiparous and multiparous women separately, using the split-sample cross-validation technique.

MAIN OUTCOME MEASURE

Preterm birth, defined as birth occurring before 259 days of gestation.

RESULTS

Preterm birth rates for primiparous and multiparous women were 54 and 53 per 1000 births, respectively. In primiparous women low maternal age (under 20 years) was the only sociodemographic variable that was predictive of preterm birth (P = 0.01). However, only 10.7% of preterm birth among primiparous women was associated with low maternal age. In multiparous women, using univariable analysis, employment status was statistically significantly associated with preterm birth. This association disappeared when employment status was adjusted for by other variables in the model. Social class was not predictive of preterm birth in either primiparous or multiparous women.

CONCLUSION

From the results of this study it is concluded that sociodemographic factors do not have a substantial impact on the risk of preterm birth. It seems unlikely that preventative measures aimed at social-demographic adversity will reduce preterm birth rates.

[Fetal growth in premature infants in Haute-Normandie]

BACKGROUND

Fetal growth standards of preterm infants are different from one study to another, especially for extremely preterm babies.

POPULATION AND METHODS

Between 1976 and 1990, a cross-sectional study of the resulting intrauterine growth of premature newborns from Haute-Normandie (France) was conducted by collecting data of the compulsory health certificate set up in the first week after birth. In spite of exclusions, curves for obstetrical terms ranging from 28 to 36 weeks of gestational age were settled. Equivalents of 8,042 birth weights, 7,792 statures, 8,041 head circumferences and 6,737 ponderal index were used.

RESULTS

Comparing our results with those published in the literature, we observed short differences for mean or middle values: from less than 170 to more than 180 g for weight, from less than 1 to more than 2.6 cm for stature and from less than 1 to more than 1.9 cm for head circumference.

CONCLUSION

The selected normal lower threshold for each parameter and the varieties of fetal growth inadequacy are under discussion.