Risk factors for spontaneous preterm birth in two urban areas of Ukraine

Maternal height and the risk of preterm birth and low birth weight: a systematic review and meta-analyses

OBJECTIVE

Preterm birth (PTB) and low birth weight (LBW) are the leading causes of neonatal morbidity and mortality, but the effect of maternal height on these outcomes continues to be debated. Our objective was to determine the relationships between maternal height and PTB and LBW.

DATA SOURCES

Medline and EMBASE were searched from their inceptions.

STUDY SELECTION

Studies with a reference group that assessed the effect of maternal height on PTB (< 37 weeks) and LBW (< 2500 grams) in singletons were included.

DATA EXTRACTION

Data were extracted independently by two reviewers.

DATA SYNTHESIS

Fifty-six studies were included involving 333 505 women. In the cohort studies, the unadjusted risk of PTB in short-statured women was increased (relative risk [RR] 1.23; 95% CI 1.11 to 1.37), as was the unadjusted risk of LBW (RR 1.81; 95% CI 1.47 to 2.23), although not all of the studies with adjusted data found the same association. Maternal tall stature was not associated with PTB (unadjusted RR 0.97; 95% CI 0.82 to 1.14), although LBW was decreased (unadjusted RR 0.56; 95% CI 0.46 to 0.69), but not in the adjusted data.

CONCLUSION

From our complete systematic review and meta-analyses, to our knowledge the first in this area, we conclude that short-statured women have higher unadjusted risks of PTB and LBW and tall women have approximately one half the unadjusted risk of LBW of women of reference height.

Interaction between maternal passive smoking during pregnancy and CYP1A1 and GSTs polymorphisms on spontaneous preterm delivery

OBJECTIVE

The present study aimed to examine the association between maternal passive smoking during pregnancy and the risk of spontaneous PTD and to explore the potential interaction of the single or joint gene polymorphism of CYP1A1 and GSTs with maternal passive smoking on the risk of spontaneous PTD.

METHOD

We investigated whether the association between maternal passive smoking and PTD can be modified by 2 metabolic genes, i.e. cytochrome P4501A1 (CYP1A1) and glutathione S-transferases (GSTs), in a case-control study with 198 spontaneous preterm and 524 term deliveries in Shenzhen and Foshan, China. We used logistic regression to test gene-passive smoking interaction, adjusting for maternal socio-demographics and prepregnancy body mass index.

RESULTS

Overall, maternal passive smoking during pregnancy was associated with higher risk of PTD (adjusted odds ratio = 2.20 [95% confidence interval: 1.56-3.12]). This association was modified by CYP1A1 and GSTs together, but not by any single genotype. For cross-categories of CYP1A1 Msp I and GSTs, maternal passive smoking was associated with higher risk of PTD among those women with CYP1A1 "TC/CC"+ GSTs "null", but not among women with other genotypes; and this interaction was significant (OR = 2.66 [95% CI: 1.19-5.97]; P-value: 0.017). For cross-categories of CYP1A1 BsrD I and GSTs, maternal passive smoking was associated with higher risk of PTD only among those women with CYP1A1"AG/GG"+ GSTs "null", but not among women with other genotypes; and this interaction was significant (OR = 3.00 [95% CI: 1.17-7.74]; P-value: 0.023).

CONCLUSIONS

Our findings suggest that the combined genotypes of CYP1A1 and GSTs can help to identify vulnerable pregnant women who are subject to high risk of spontaneous PTD due to passive smoking.

Consanguinity: a risk factor for preterm birth at less than 33 weeks' gestation

Consanguinity promotes homozygosity of recessive susceptibility gene variants and can be used to investigate a recessive component in diseases whose inheritance is uncertain. The objective of this study was to assess the association between consanguinity and preterm birth (PTB), stratified by gestational age and clinical presentation (spontaneous vs. medically indicated). Data were collected on 39,745 singleton livebirths without major birth defects, admitted to 19 hospitals in Lebanon, from September 2003 to December 2007. Deliveries before completed 33 weeks' gestation and deliveries at 33-36 weeks' gestation were compared, with respect to cousin marriage, with those after completed 36 weeks' gestation by using multinomial multiple logistic regression. Overall, infants of consanguineous parents had a statistically significant 1.6-fold net increased risk of being born at less than 33 weeks' gestation compared with infants of unrelated parents. This association was statistically significant only with spontaneous PTB. There was no increased risk of being born at 33-36 weeks' gestation associated with consanguinity for both clinical presentations of PTB. Our findings support a genetic contribution to early onset PTB and suggest that early PTB should be targeted in future genetic studies rather than the classic lumping of all births less than 37 weeks' gestation.

Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses

BACKGROUND

Despite the current obesity epidemic, maternal underweight remains a common occurrence with potential adverse perinatal outcomes. Our objective was to determine the relationship between maternal underweight and preterm birth (PTB) and low birth weight (LBW) in singleton pregnancies in developing and developed countries.

METHODS

We followed the MOOSE consensus statement. We searched MEDLINE and EMBASE from their inceptions. We included studies that assessed the effect of maternal underweight compared with normal weight according to body mass index in singleton gestations on our two primary outcomes: PTB (<37 weeks) and LBW (<2500 g). Two assessors independently reviewed citations, extracted data and assessed quality.

RESULTS

A total of 78 studies were included involving 1 025 794 women. The overall risk of PTB was increased in the cohort studies of underweight women [adjusted relative risk (RR) 1.29, 95% confidence interval (CI) 1.15-1.46], as were the risks of spontaneous PTB (adjusted RR 1.32, 95% CI 1.10-1.57) and induced PTB (adjusted RR 1.21, 95% CI 1.07-1.36). Underweight women had an increased risk of an LBW infant (adjusted RR 1.64, 95% CI 1.38-1.94). In developed countries, underweight women had an increased risk of PTB (RR 1.22, 95% CI 1.15-1.30) but not in developing countries (RR 0.99, 95% CI 0.67-1.45). In both developed and developing countries, underweight women were at increased risk of having an LBW infant (RR 1.48, 95% CI 1.29-1.68, and RR 1.52, 95% CI 1.25-1.85, respectively).

CONCLUSIONS

In this systematic review and meta-analyses, we determined that singletons born to underweight women have higher risks of PTB (overall, spontaneous and induced) and LBW than those born to women with normal weight.

Effect of psychosocial stress and physical activity on preterm birth: a cohort study

AIM

To determine trimester-specific effects of risk factors for preterm birth (PTB).

METHODS

A prospective study was carried out in a district of Sri Lanka. A total of 885 pregnant mothers were recruited at equal to or less than 16 weeks of gestation and followed up until partus. Trimester-specific exposure statuses and potential confounding factors were gathered on average at the 12th, 28th, and 36th weeks of gestation. Physical activities were assessed by obtaining information about the duration of specific postures adopted per day by housewives during each trimester at home and both at home and during working hours for those who were engaged in paid employment. Psychosocial stress was assessed using the Modified Life Events Inventory and the General Health Questionnaire 30. Multiple logistic regression analysis was applied and the results were expressed as adjusted odds ratios (OR) and 95% confidence intervals (95%CI).

RESULTS

Standing equal to or less than 2.5 h/day during the first or second or both trimesters (OR 1.83, 95%CI 1.03, 3.25), maternal age of <25 years (OR 1.73, 95%CI 1.02, 2.95), education up to primary school level (OR 3.30, 95%CI 1.3, 8.36) and past history of low birthweight (OR 2.52, 95%CI 1.16, 5.48) were risk factors for PTB. Psychosocial stress was not found to be a risk factor for PTB.

CONCLUSIONS

Standing equal to or less than 2.5 h/day during the early trimesters was a risk factor for PTB among uncomplicated pregnancies. Further studies are recommended to assess the trimester-specific effect of psychosocial stress on PTB.

Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analyses

OBJECTIVE

To determine the relation between overweight and obesity in mothers and preterm birth and low birth weight in singleton pregnancies in developed and developing countries.

DESIGN

Systematic review and meta-analyses.

DATA SOURCES

Medline and Embase from their inceptions, and reference lists of identified articles.

STUDY SELECTION

Studies including a reference group of women with normal body mass index that assessed the effect of overweight and obesity on two primary outcomes: preterm birth (before 37 weeks) and low birth weight (<2500 g).

DATA EXTRACTION

Two assessors independently reviewed titles, abstracts, and full articles, extracted data using a piloted data collection form, and assessed quality.

DATA SYNTHESIS

84 studies (64 cohort and 20 case-control) were included, totalling 1 095 834 women. Although the overall risk of preterm birth was similar in overweight and obese women and women of normal weight, the risk of induced preterm birth was increased in overweight and obese women (relative risk 1.30, 95% confidence interval 1.23 to 1.37). Although overall the risk of having an infant of low birth weight was decreased in overweight and obese women (0.84, 0.75 to 0.95), the decrease was greater in developing countries than in developed countries (0.58, 0.47 to 0.71 v 0.90, 0.79 to 1.01). After accounting for publication bias, the apparent protective effect of overweight and obesity on low birth weight disappeared with the addition of imputed "missing" studies (0.95, 0.85 to 1.07), whereas the risk of preterm birth appeared significantly higher in overweight and obese women (1.24, 1.13 to 1.37).

CONCLUSIONS

Overweight and obese women have increased risks of preterm birth and induced preterm birth and, after accounting for publication bias, appeared to have increased risks of preterm birth overall. The beneficial effects of maternal overweight and obesity on low birth weight were greater in developing countries and disappeared after accounting for publication bias.

Pregnancies and births among adolescents: a population-based prospective study in rural Vietnam

OBJECTIVE

To describe birth rates and pregnancy outcomes, specifically stillbirth, preterm delivery and low birth weight (LBW) in relation to socio-demographic characteristics, among adolescent women in a rural district in northern Vietnam.

MATERIAL AND METHOD

Within an epidemiological field laboratory, quarterly surveillance of 7767 adolescent women in the ages 15-19 during the period January 1999 to December 2005 was conducted. Birth rates were calculated and pregnancy outcomes were described in relation to background factors.

RESULT

A total of 1021 pregnancies were reported by 926 adolescent women during the period of whom 17% were below 18 years. The estimated adolescent birth rate during 1999-2005 was 27/1000 women-years. The incidence of stillbirth among all births was 19/1000 births. These were more likely to be delivered preterm. The incidence of preterm deliveries and LBW infants was 193 and 75 per 1000 live births, respectively. There were no differences in socio-demographic background for stillbirth, preterm delivery or LBW.

CONCLUSION

Adolescent birth rates were similar to those found in the recent Vietnamese DHS and considerably lower than the average for South-East Asia. Higher rates of stillbirth and preterm delivery were found than those previously reported for Vietnam, indicating the need for careful monitoring of adolescent pregnancies and their infants. Further research is needed to explore if and how much socio-demographic variables influence pregnancy outcome, comparing more differentiated groups, as a basis for interventions to assure access to adequate reproductive health care services for all women.

Inequalities in birth outcomes in Russia: evidence from Tula oblast

This paper describes pregnancy outcomes and identifies their determinants in a Russian region, in the year 2000. It includes all births and perinatal deaths recorded as occurring in Tula oblast. The socio-economic correlates of adverse outcomes are explored using logistic regression; outcomes and their determinants are compared with other countries. Perinatal mortality in Tula in 2000 was 16.8/1000 births. The frequencies of low birthweight, low ponderal index and preterm birth were higher in Tula than in other industrialised countries. Mean birthweight increased with increasing education and was higher in married than in single mothers, and higher in ethnic Russians than in others. Survival in the perinatal period was substantially lower at all birthweights than in Sweden, which has the lowest neonatal mortality rate in Europe. There are wide inequalities in fetal development in Russia, especially in relation to maternal education, and the adverse outcomes appear to reflect a combination of adverse fetal development (implying the need for policies that improve the health of prospective mothers) and poor survival (implying the need for more effective care for newborn infants).

Large social disparities in spontaneous preterm birth rates in transitional Russia

OBJECTIVE

This study estimated the effect of maternal sociodemographic, obstetric and lifestyle factors on the risk of spontaneous preterm birth in a Russian town.

METHODS

All women with singleton pregnancies registered at prenatal care centres in Severodvinsk in 1999 comprised the cohort for this study (n=1559). Analysis was based on spontaneous live singleton births at the maternity home (n=1103). Multivariable logistic regression was applied to quantify the effect of the studied factors on the risk of preterm birth. Differences in gestation duration were studied using multiple linear regression.

RESULTS

In total, 5.6% of all spontaneous births were preterm. Increased risks of preterm delivery were found in women with lower levels of education and in students. Placental complications, stress and a history of fetal death in previous pregnancies were also associated with elevated risks for preterm delivery. Smoking, hypertension and multigravidity were associated with reduced length of pregnancy in metric form.

CONCLUSION

In addition to medical risk factors, social factors are important determinants of preterm birth in transitional Russia. Large disparities in preterm birth rates may reflect the level of inequalities in transitional Russia. Social variations in pregnancy outcomes should be monitored.

Preterm birth rates in Avon County, England, and urban Ukraine

OBJECTIVE

We compared rates of total and spontaneous preterm birth in Avon County, England and urban Ukraine to explore whether adverse conditions in the former eastern bloc influenced the preterm rate.

STUDY DESIGN

Women who had last menstrual period (LMP) in a specified time window were recruited from geographically defined areas. Data were gathered between 1992 and 1995, using maternal questionnaires and medical record abstraction, with comparable methods in both sites insofar as possible. There were 13731 births in Avon and 3087 in Ukraine. Rates of total and spontaneous preterm births were compared, taking account of maternal characteristics and other relevant variables.

RESULTS

The total preterm birth rates were similar (5.9%, Ukraine; 5.5%, Avon) but the spontaneous preterm rate was about 60% higher in Ukraine (5.0% versus 3.1%). Maternal characteristics and measurement differences did not explain the discrepancy.

CONCLUSION

The difference in the spontaneous preterm rates may reflect differences in obstetrical management resulting from shortages of medical supplies and equipment in Ukraine.

Risk factors for preterm birth in Vietnam

OBJECTIVE

To identify the risk of preterm birth and possible determinants among women in Hanoi, Vietnam.

METHOD

Prospective cohort study of 1709 women with singleton live births at Hanoi Obstetrics and Gynecology Hospital, Hanoi, Vietnam, June-October 2002. Logistic regression analysis was used to examine predictors of preterm birth (<37 weeks' gestation).

RESULT

The risk of preterm birth was 11.8%. Physically demanding work during pregnancy, two or more prior spontaneous abortions, history of preterm birth, vaginal bleeding, inadequate prenatal care during the first 20 weeks of gestation, and history of intrauterine device use with removal less than 12 months before the current pregnancy were associated with increased risk of preterm birth (adjusted odds ratios between 1.8 and 2.6).

CONCLUSION

Preterm birth is relatively frequent in this population. Beyond established risk factors, these data implicated agricultural work and physical work demands with preterm birth, as well as history of recent IUD use.