Recurrence of preterm birth in singleton and twin pregnancies

OBJECTIVE: To assess recurrence of preterm birth and its impact on an obstetric population. METHODS: Women with consecutive births at our hospital beginning with their first pregnancy were identified (n = 15,945). The first pregnancy was categorized as delivered between 24 and 34 weeks' gestation or 35 weeks or beyond, singleton or twin, and spontaneous or induced. The risk of preterm delivery in these same women during subsequent pregnancies was then analyzed. RESULTS: Compared with women who delivered a singleton at or beyond 35 weeks' gestation in their first pregnancy, those who delivered a singleton before 35 weeks were at a significant increased risk for recurrence (odds ratio [OR] 5.6, 95% confidence interval [CI] 4.5, 7.0), whereas those who delivered twins were not (OR 1.9, 95% CI 0.46, 8.14). The OR for recurrent spontaneous preterm birth presenting with intact membranes was 7.9 (95% CI 5.6, 11.3) compared with 5.5 (95% CI 3.2, 9.4) with ruptured membranes. Of those women with a recurrent preterm birth, 49% delivered within 1 week of the gestational age of their first delivery and 70% delivered within 2 weeks. Among 15,863 nulliparous women with singleton births at their first delivery, a history of preterm birth in that pregnancy could predict only 10% of the preterm births that ultimately occurred in the entire obstetric population. CONCLUSION: In a population-based study at our hospital, women who initially delivered preterm and thus were identified to be at risk for recurrence ultimately accounted for only 10% of the prematurity problem in the cohort.     

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.     

Early preterm delivery due to placenta previa is an independent risk factor for a subsequent spontaneous preterm birth

ABSTRACT: BACKGROUND: To determine whether patients with placenta previa who delivered preterm have an increased risk for recurrent spontaneous preterm birth. METHODS: This retrospective population based cohort study included patients who delivered after a primary cesarean section (n = 9983). The rate of placenta previa, its recurrence, and the risk for recurrent preterm birth were determined. RESULTS: Patients who had a placenta previa at the primary CS pregnancy had an increased risk for its recurrence [crude OR of 2.65 (95 % CI 1.3-5.5)]. The rate of preterm birth in patients with placenta previa in the primary CS pregnancy was 55.9 %; and these patients had a higher rate of recurrent preterm delivery than the rest of the study population (p < .001). Among patients with placenta previa in the primary CS pregnancy, those who delivered preterm had a higher rate of recurrent spontaneous preterm birth regardless of the location of their placenta in the subsequent delivery [OR 3.09 (95 % CI 2.1-4.6)]. In comparison to all patients with who had a primary cesarean section, patients who had placenta previa and delivered preterm had an independent increased risk for recurrent preterm birth [OR of 3.6 (95 % CI 1.52-8.51)]. CONCLUSIONS: Women with placenta previa, who deliver preterm, especially before 34 weeks of gestation, are at increased risk for recurrent spontaneous preterm birth regardless to the site of placental implantation in the subsequent pregnancy. Thus, strict follow up by high risk pregnancies specialist is recommended.     

Short interpregnancy interval and risk of spontaneous preterm delivery

OBJECTIVES: Short interpregnancy intervals are related to increased prevalence of adverse perinatal outcomes. However, the reported association with preterm birth might be due to confounding by factors such as previous pregnancy outcomes, socioeconomic level or lifestyles. The objective of this study was to evaluate the effect of short interpregnancy interval on the occurrence of spontaneous preterm delivery. STUDY DESIGN: The prevalence of a short interpregnancy interval, defined as six or less months between a preceding delivery or abortion and the last menstrual period before index pregnancy, was compared between 263 spontaneous preterm (<37 weeks) and 299 term (37-42 weeks) consecutive births. Separate analyses were performed for early (<34 weeks) and late (34-36 weeks) preterm deliveries. Crude and adjusted odds ratios (ORs) and 95% confidence intervals (CI) were calculated using unconditional logistic regression. RESULTS: There was a significant association between short interpregnancy interval and spontaneous early preterm delivery, both crude (OR=3.9; 95% CI: 1.91-8.10) and adjusted for maternal age, school education, previous birth outcomes, antenatal care, smoking habits, body mass index and gestational weight gain (adj(OR)=3.6; 95% CI: 1.41-8.98). No significant effect on spontaneous late preterm delivery was found (crude(OR)=0.8; 95% CI: 0.32-1.83). CONCLUSIONS: This study showed that short interpregnancy intervals significantly increased the risk of early spontaneous preterm birth but no such effect was evident for late preterm deliveries.     

Recurrence risk of preterm birth due to preeclampsia.

There may be an increased risk of preterm birth due to preeclampsia among women whose previous pregnancies ended in preterm birth due to preeclampsia. We studied 1,130 women who delivered 2 successive singleton infants in our hospital, excluding women who delivered an abnormally formed infant during the study period. We reviewed the gestational week at delivery in these 2,260 pregnancies and found a total of 182 preterm deliveries (8.1%) by 156 women. The causes of preterm birth were reviewed. Failed tocolysis, including premature rupture of membranes and clinical chorioamnionitis, and preeclampsia accounted for 135 (74.2%) and 30 (16.5%) of the 182 preterm deliveries, respectively. Women whose 1st delivery was preterm had a 3.26 times (95% CI 2.21-4.79) higher risk of a subsequent preterm delivery than women whose 1st delivery was term (26/96 vs. 60/1,034). The risk of preeclampsia-related preterm delivery was 54.4 times (17.2 to 172.5) higher in women with a previous preeclampsia-related preterm delivery than in women with a previous term delivery (5/19 vs. 5/1034). Women who had a history of preeclampsia-related preterm birth had a greater risk of preeclampsia-related preterm birth in a subsequent pregnancy as compared with women with a previous term birth.     

Risk of preterm birth that is associated with vaginal douching

OBJECTIVE: The purpose of this study was to examine the association between vaginal douching and preterm birth. STUDY DESIGN: We enrolled hospitalized women after delivery in a case-control study. Women who were delivered of a live preterm singleton infant were assigned as cases. Women who were delivered at term were randomly selected as control subjects. We surveyed women about their douching habits and risk factors for preterm birth and abstracted data from the records. RESULTS: After adjustment, vaginal douching within 6 months of pregnancy was not significantly associated with preterm birth (odds ratio, 1.1; 95% CI, 0.8-1.6). However, in secondary analyses, douching more than once per week (odds ratio, 4.0; 95% CI, 1.0-15.5) or longer than 10 years (odds ratio, 1.9; 95% CI, 1.1-3.2) was associated with preterm birth. CONCLUSION: Vaginal douching does not appear to be a strong risk factor for preterm birth. Further study is needed to confirm the risk that is associated with frequent or long-term douching.     

Interpregnancy interval and the risk of preterm birth in Thrace,Greece

OBJECTIVE: To examine the influence of short interpregnancy interval on the prevalence of preterm birth in two, ethically different, Greek populations. STUDY DESIGN: We studied 652 urban Christian women and 578 rural, Romany, Muslim women who had had two consecutive, singleton pregnancies. We related the prevalence of preterm birth to the interpregnancy intervals (cut-off point, 6 months). Student's t-test, x(2)-test and relative risk estimation were used. RESULTS: Preterm birth and interpregnancy intervals less than 6 months occurred more often among Muslims than Christians. Among Muslims, an interval of <6 months was associated with greater prevalence of preterm birth (16% versus 7.3%, P=0.013, RR=2.4 and 95% C.I. 1.3-4.7). Christians did not demonstrate a similar relationship. CONCLUSIONS: A short interpregnancy interval seems to be a risk factor for preterm birth in the population of rural, Romany, Muslim women.     

Risk of preterm delivery in relation to maternal low birth weight

OBJECTIVE: We examined the relationship between maternal low birth weight and preterm delivery risk. METHODS: Information concerning maternal birth weight was collected during in-person interviews. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI). Preterm delivery cases were studied in aggregate, in subgroups (spontaneous preterm labor, preterm premature rupture of membranes, medically induced preterm delivery, moderate preterm delivery [gestational age at delivery 34-36 weeks], and early preterm delivery [gestational age at delivery<34 weeks]). RESULTS: After adjusting for confounders, women weighing<2,500 g at birth had a 1.54-fold increased risk of preterm delivery versus women weighing=2,500 g (95% CI 0.97-2.44). Maternal low birth weight was associated with a 2-fold increased risk of spontaneous preterm delivery (95% CI 1.03-3.89), but weakly associated with preterm premature rupture of membranes (OR=1.44; 95% CI 0.67-3.09) and medically induced preterm delivery (OR=1.10; 95% CI 0.43-2.82). Maternal low birth weight was more strongly associated with early preterm delivery (OR=1.94) than with moderate preterm delivery (OR=1.46). Women weighing<2,500 g at birth and who became obese (pre-pregnancy body mass index, =30 kg/m2) before pregnancy had a 3.65-fold increased risk of preterm delivery (95% CI 1.33-10.02) versus women weighing=2,500 g at birth and who were not obese prior to pregnancy (<30 kg/m2). CONCLUSIONS: Results confirm earlier findings linking maternal low birth weight with future risk of preterm delivery.     

Risk of recurrent preterm birth and placental pathology

OBJECTIVE: To estimate whether placental pathological lesions from an index preterm birth are associated with an increased risk of recurrent preterm birth and to estimate whether certain pathologic lesions recur in a woman's next delivery. METHODS: We performed a retrospective cohort study of all women who delivered at less than 37 weeks and had their next delivery at our institution during a 5-year period. Women were included in the cohort if placental pathology was available from their preterm birth. Placental pathology from their subsequent birth was also collected. Placental pathology was classified into presence or absence of two classes of lesions-inflammatory and thrombotic. Variables considered as possible confounders included race, gestational age of preterm birth, interpregnancy interval, tobacco use, payor status, years of education, and maternal medical problems. RESULTS: Inflammatory lesions (n=173) were associated with recurrent preterm birth overall as well as recurrent spontaneous preterm birth (P<.001). Thrombotic lesions (n=158) were not associated with recurrent preterm birth or any subtypes of preterm birth. The association between inflammatory lesions and recurrent spontaneous preterm birth remained significant when controlling for gestational age of preterm birth, race, and tobacco use, with an adjusted odds ratio of 2.4 (95% confidence interval 1.2-4.7). Inflammatory placental lesions (n=194) were associated with inflammatory lesions in the subsequent delivery P=.001). CONCLUSION: Recurrent preterm birth is more likely among women with inflammatory lesions on placental pathology from a prior preterm birth. Additionally, these women are more likely to have placental inflammatory lesions with their next delivery. LEVEL OF EVIDENCE: II.     

Low birth weight,preterm birth and short interpregnancy interval in Sudan

Objective.?To investigate whether short interpregnancy interval (IPI) is associated with increased risk of low birth weight and preterm labour.

Methods.?The study was conducted in the labour ward of Khartoum hospital in Sudan during November 2007 through February 2008. Odds ratios (ORs) were adjusted for the confounding factors using multiple logistic regression models.

Results.?Compared with IPI of 18–30 months, those women with intervals shorter than 18 months had an increased risk of low birth weight (OR = 1.9, 95% CI = 1.0–3.5, P = 0.04) and preterm labour (OR = 2.3, 95% CI = 1.1–4.7, P = 0.01).

Conclusion.?In this study, IPI shorter than 18 months are independently associated with increased risk of adverse perinatal outcomes.     

Is small for gestational age a marker of future fetal survival in utero?

OBJECTIVE: We sought to assess whether small for gestational age is a risk factor for stillbirth of a subsequent sibling. METHODS: The Missouri maternally linked cohort data set, containing data on births from 1978 through 1997, was used. We identified the study group (women who delivered a SGA infant in the first pregnancy) and a comparison group (women who delivered a non-SGA infant in their first pregnancy) and compared the outcome (stillbirth) in the second pregnancy between both groups. RESULTS: We analyzed information on the first and second pregnancies of 402,015 women (43,549 [10.8%] in the study arm and 358,466 [89.2%] in the comparison arm). Of the 1,883 cases of stillbirth in the second pregnancy, 314 cases occurred in mothers with a history of SGA (stillbirth rate 7.2/1,000) and 1,569 in the comparison group (stillbirth rate 4.4/1,000), P < .001. The adjusted risk of stillbirth was 60% higher in women with a prior SGA (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.4-1.8). The risk for stillbirth in the second pregnancy increased with decreasing gestational age at birth of the SGA infant in the first pregnancy (term: OR 1.4, 95% CI 1.2-1.6; preterm: OR 2.8, 95% CI 2.0-3.8; and very preterm: OR 4.2, 95% CI 2.4-7.3), P for trend < .001. CONCLUSION: Small for gestational age is a marker for subsequent stillbirth, and the risk rises with decreasing gestational age of the SGA birth. This information is potentially useful for counseling parents of SGA infants. LEVEL OF EVIDENCE: II-2.     

Choice and chance: determinants of short interpregnancy intervals in Denmark

BACKGROUND: It is still unclear whether short interpregnancy intervals are a marker for women at risk of poor pregnancy outcome or a direct risk factor for poor perinatal outcomes. The study objective was to identify risk factors associated with short interpregnancy intervals in Denmark. METHODS: From a cohort of pregnant women in a geographically defined area in Denmark (n=11,288) and using register linkage, we identified 5756 multiparous mothers who completed a detailed interview on social behavior during pregnancy. We restricted our analysis to 2904 mothers who had an interpregnancy interval of less than 37 months. Multiple logistic regression was used to estimate the Odds Ratio (OR) of having a short interval as a function of a number of determinants. RESULTS: About 4.8% of the mothers had an interpregnancy interval less than 9 months. Short interpregnancy intervals were more likely to occur in an unplanned pregnancy (OR=2.9, 95% CI: 2.2-3.9), to follow irregular menstruation (OR=1.7, 95% CI: 1.1, 2.5) and to occur in older (OR=1.7, 95% CI: 1.1, 2.5) and high parity mothers (OR=1.9, 95% CI: 1.1, 3.1). Poor housing, smoking and low social status were also associated with short interpregnancy interval CONCLUSION: Short interpregnancy intervals may be a marker for women at risk and these risk factors differ among populations. They also appear to be a result of choice (e.g. in older women). Biological factors also play a significant role in determining short interpregnancy intervals.     

The recurrence risk of adverse outcome in the second pregnancy in women with rheumatic disease1

OBJECTIVE: To study recurrence risks of adverse pregnancy outcome in the second pregnancy in women with rheumatic disease. METHODS: In a national population-based cohort study, women with rheumatic disease recorded from 1967 to 1995 in the Medical Birth Registry of Norway were compared with mothers without such diagnoses with regard to recurrence risks of adverse pregnancy outcomes in the second pregnancy. The odds ratios (ORs) of all outcomes were adjusted for maternal age, those of cesarean delivery for time period, and those of preeclampsia for interpregnancy interval. RESULTS: Women with rheumatic disease an dadverse pregnancy outcome in the first pregnancy had a statistically significant higher recurrence risk of the same event in the second pregnancy than women without rheumatic disease (preeclampsia: OR 2.22; 95% confidence interval [CI] 1.18, 4.19) (cesarean delivery: OR 1.52; 95% CI 1.05, 2.21) (preterm birth: OR 1.86; 95% CI 1.12, 3.11). In women with rheumatic disease diagnosed between the first and second births, a significantly increased recurrence risk of low birth weight occurred. Women with rheumatic disease also had a higher occurrence of markers for placental dysfunction (preeclampsia, preterm birth, or small for gestational age) in the second birth after any of these outcomes in the first birth (OR 1.35; 95% CI 1.02, 1.78) (35.1% versus 29.2%). CONCLUSION: The recurrence risk of an adverse outcome in the second pregnancy is increased in any woman, but was even higher in women with a rheumatic disease. These patients should be counseled accordingly, be closely monitored during pregnancy, and have access to appropriate subspecialists.     

History of abortion, preterm and term birth, and risk of gestational hypertension: a population-based study

OBJECTIVE: To examine the consequence of prior abortion and preterm and term birth on the occurrence of gestational hypertension in the subsequent pregnancy. STUDY DESIGN: A population-based, retrospective, cohort study was conducted based on 140,773 pregnancies delivered between 1993 and 1999 in 49 hospitals in northern and central Alberta, Canada. Multivariate logistic regression was applied to estimate ORs with 95% CIs, adjustedfor confounding variables. RESULTS: The incidence of gestational hypertension was markedly lower in women who previously delivered at term than in primigravid women (2.4% vs. 5.6%) (adjusted OR [aOR]: .41 [.38-.44], p < 0.001). The incidence of gestational hypertension in women with previous preterm birth but without prior abortion or term pregnancy was also lower than in primiparous women (3.9% vs. 5.6%) (aOR: .72 [.54-.95], p<0.05). Moreover, there was a trend toward a decreased incidence of gestational hypertension among women with a longer duration of previous preterm gestation. Although there was a statistically significant decreased incidence of gestational hypertension in pregnancies in women with a previous history of abortion (4.9%) as compared to women without such a history (5.6%) (aOR:.85[95% CI: .77-.93], p < 0.05), 2, 3 or more abortions were not associated with a decreased risk of gestational hypertension, calling into question the clinical significance of the effect of abortion. CONCLUSION: There was a trend toward a decreased incidence of gestational hypertension among women with a longer duration of previous gestation. However, a history of term pregnancy (> or =37 weeks) conveyed the most substantial protection against gestational hypertension in the subsequent pregnancy.     

The influence of interpregnancy interval on the subsequent risk of stillbirth and early neonatal death

OBJECTIVE: To study whether interpregnancy interval is associated with increased risks of stillbirth and early neonatal death and whether this possible association is confounded by maternal characteristics and previous reproductive history. METHODS: In a Swedish nationwide study of 410,021 women's first and second singleton deliveries between 1983 and 1997, we investigated the influence of interpregnancy interval on the subsequent risks of stillbirth and early neonatal death. Odds ratios (ORs) with 95% confidence intervals (CIs) estimated using unconditional logistic regression were adjusted for maternal characteristics and previous pregnancy outcome categorized into stillbirth, early neonatal death, preterm, or small for gestational age delivery. RESULTS: Compared with interpregnancy intervals between 12 and 35 months, very short interpregnancy intervals (0-3 months) were, in the univariate analyses, associated with increased risks of stillbirth and early neonatal death (crude OR 1.9; 95% CI 1.3, 2.7; and 1.8; 1.2, 2.8, respectively). However, after adjusting for maternal characteristics and previous reproductive history, women with interpregnancy intervals of 0 to 3 months were not at increased risks of stillbirth (adjusted OR 1.3; 95% CI 0.8, 2.1) or early neonatal death (adjusted OR 0.9; 95% CI 0.5, 1.6). Women with interpregnancy intervals of 72 months and longer were at increased risk of stillbirth (adjusted OR 1.5; 95% CI 1.1, 2.1) and possibly early neonatal death (adjusted OR 1.3; 95% CI 0.9, 2.1). CONCLUSION: Short interpregnancy intervals appear not to be causally associated with increased risk of stillbirth and early neonatal death, whereas long interpregnancy intervals were associated with increased risk of stillbirth and possibly early neonatal death.     

Effect of the interpregnancy interval on perinatal outcomes in Latin America

OBJECTIVE: To estimate whether interpregnancy interval is independently associated with increased risk of perinatal death and other adverse perinatal outcomes. METHODS: We investigated the effect of interpregnancy interval on perinatal outcomes in 1,125,430 pregnancies recorded in the Perinatal Information System database of the Latin American Center for Perinatology and Human Development, Montevideo, Uruguay, between 1985 and 2004. Odds ratios (ORs) were adjusted for 16 major confounding factors using multiple logistic regression models. RESULTS: Compared with infants with interpregnancy intervals of 18-23 months, those born to women with intervals shorter than 6 months had an increased risk of early neonatal death (adjusted OR 1.49, 95% confidence interval [CI] 1.06-1.96), fetal death (adjusted OR 1.54, 95% CI 1.28-1.83), low birth weight (adjusted OR 1.88, 95% CI 1.78-1.90), very low birth weight (adjusted OR 2.01, 95% CI 1.73-2.31), preterm birth (adjusted OR 1.80, 95% CI 1.71-1.89), very preterm birth (adjusted OR 1.95, 95% CI 1.67-2.26), and small for gestational age (adjusted OR 1.30, 95% CI 1.25-1.36). Intervals of 6-11 months and 60 months and longer were also associated with a significantly greater risk for the 7 adverse perinatal outcomes. CONCLUSION: In Latin America, interpregnancy intervals shorter than 12 months and longer than 59 months are independently associated with increased risk of adverse perinatal outcomes. These data suggest that spacing pregnancies appropriately could prevent perinatal deaths and other adverse perinatal outcomes in the developing world.     

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.     

Precancerous changes in the cervix and risk of subsequent preterm birth

OBJECTIVE: The aims of this study were (i) to examine whether women referred for assessment of precancerous changes in the cervix had higher rates of preterm birth compared with those in the general population and (ii) to compare preterm birth rates for treated and untreated women adjusting for possible confounding factors. DESIGN: Retrospective cohort design. SETTING: Teaching hospital. POPULATION: All women referred to the Royal Women's Hospital, Melbourne (1982-2000), who subsequently had a birth recorded on the Victorian Perinatal Data Collection system (n = 5548). METHODS: Record linkage of hospital dysplasia clinic records and population-based birth records. MAIN OUTCOME MEASURES: Total preterm delivery (<37 weeks of gestation) and subtypes. RESULTS: Both treated and untreated women were at a significantly increased risk for preterm birth compared with those in the general population: treated--standardised prevalence ratio (SPR) 2.0, 95% CI 1.8-2.3 and untreated--SPR 1.5, 95% CI 1.4-1.7. Within the cohort, the treated women were significantly more likely to give birth preterm (adjusted OR 1.23, 95% CI 1.01-1.51). An increased risk of preterm birth was also associated with a history of induced or spontaneous abortions, illicit drug use during pregnancy or a major maternal medical condition. Cone biopsy, loop electrosurgical excision procedure and diathermy were associated with preterm birth. After adjusting for possible confounding factors, only diathermy remained significant (adjusted OR 1.72, 95% CI 1.36-2.17). Women treated using laser ablation were not at an increased risk for preterm birth (adjusted OR 1.1, 95% CI 0.8-1.4). CONCLUSIONS: Diagnosis of precancerous changes in the cervix (regardless of the treatment) was associated with an increased risk of preterm birth. Consideration should be given to the preferential use of ablative treatments.     

A polymorphism in the promoter region of TNF and bacterial vaginosis: preliminary evidence of gene-environment interaction in the etiology of spontaneous preterm birth

OBJECTIVE: The rarer of 2 alleles of a polymorphism in the promoter of the tumor necrosis factor alpha gene (TNF) has been associated with spontaneous preterm birth following preterm premature rupture of the fetal membranes in some populations. The aim of this study was to assess if the presence of symptomatic bacterial vaginosis amplifies the risk of spontaneous preterm birth in those with a "susceptible" TNF genotype. STUDY DESIGN: A case-control study was performed at our institution. Cases (n=125) were defined as women who delivered before 37 weeks as a result of ruptured membranes or preterm labor, while control subjects (n=250) were defined as women who delivered after 37 weeks. DNA was collected from maternal blood and analyzed for the TNF genotype. Information on symptomatic bacterial vaginosis and other risk factors for preterm birth was obtained by review of the antenatal record. Multiple logistic regression was also used to test the interaction between bacterial vaginosis, the TNF genotype, and preterm birth. RESULTS: Maternal carriers of the rarer allele (TNF-2) were at a significantly increased risk of spontaneous preterm birth [odds ratio (OR) 2.7, 95% CI 1.7-4.5]. The association between TNF-2 and preterm birth was modified by the presence of bacterial vaginosis, such that those with a "susceptible" genotype and bacterial vaginosis had increased odds of preterm birth compared with those who did not (OR 6.1, 95% CI 1.9-21.0). CONCLUSION: This study provides preliminary evidence that an interaction between genetic susceptibilities (ie, TNF-2 carriers) and environmental factors (ie, bacterial vaginosis) is associated with an increased risk of spontaneous preterm birth.