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.     

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.     

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.     

The preterm prediction study: maternal serum relaxin, sonographic cervical length, and spontaneous preterm birth in twins

OBJECTIVE: The risk of spontaneous preterm birth has been related to decreased cervical length and to increased serum relaxin. To explore a relationship between these findings, we used data collected from two prior studies to correlate relaxin levels with cervical length and risk of spontaneous preterm birth in women with twin pregnancies. METHODS: In a secondary analysis of data collected in two previous observational studies of risk factors for preterm birth, relaxin levels in maternal serum and cervical length were measured at 24 (n= 188) and 28 (n= 145) weeks in women with spontaneous twin pregnancies. Relaxin, as a continuous variable, was related by logistic regression analysis to risk of spontaneous preterm birth before 37, 35, and 32 weeks' gestation, and by Spearman correlation coefficients to cervical length at 24 and 28 weeks. Cervical length at 24 weeks was known to be correlated with spontaneous preterm birth before 37, 35, and 32 weeks (P =.03,.01, and.002, respectively) in this study population. RESULTS: Cervical length did not correlate with relaxin levels at 24 (P=.601) or 28 (P=.304) weeks. Relationships between relaxin and spontaneous preterm birth were observed at 24 weeks for births before 37 weeks (odds ratio [OR] 1.56, 95% confidence interval [CI] 1.00, 2.44; P=.05), and at 28 weeks for births before 35 weeks (OR 1.97, 95% CI 1.05, 3.70; P=.034) and 32 weeks (OR 2.43, 95% CI 1.01, 5.83; P=.048). CONCLUSION: The absence of an association between relaxin and cervical length suggests that increased relaxin does not explain the inverse correlation between cervical length and spontaneous preterm birth in women with spontaneous twin pregnancies.     

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.     

Progressive periodontal disease and risk of very preterm delivery

OBJECTIVE: The goal was to estimate whether maternal periodontal disease was predictive of preterm (less than 37 weeks) or very preterm (less than 32 weeks) births. METHODS: A prospective study of obstetric outcomes, entitled Oral Conditions and Pregnancy (OCAP), was conducted with 1,020 pregnant women who received both an antepartum and postpartum periodontal examination. Predictive models were developed to estimate whether maternal exposure to either periodontal disease at enrollment (less than 26 weeks) and/or periodontal disease progression during pregnancy, as determined by comparing postpartum with antepartum status, were predictive of preterm or very preterm births, adjusting for risk factors including previous preterm delivery, race, smoking, social domain variables, and other infections. RESULTS: Incidence of preterm birth was 11.2% among periodontally healthy women, compared with 28.6% in women with moderate-severe periodontal disease (adjusted risk ratio [RR] 1.6, 95% confidence interval [CI] 1.1-2.3). Antepartum moderate-severe periodontal disease was associated with an increased incidence of spontaneous preterm births (15.2% versus 24.9%, adjusted RR 2.0, 95% CI 1.2-3.2). Similarly, the unadjusted rate of very preterm delivery was 6.4% among women with periodontal disease progression, significantly higher than the 1.8% rate among women without disease progression (adjusted RR 2.4, 95% CI 1.1-5.2). CONCLUSION: The OCAP study demonstrates that maternal periodontal disease increases relative risk for preterm or spontaneous preterm births. Furthermore, periodontal disease progression during pregnancy was a predictor of the more severe adverse pregnancy outcome of very preterm birth, independently of traditional obstetric, periodontal, and social domain risk factors. LEVEL OF EVIDENCE: II-2.     

Maternal infection and risk of cerebral palsy in term and preterm infants.

OBJECTIVE: We tested the hypothesis that term and preterm infants exposed to maternal infection at the time of delivery are at increased risk of developing cerebral palsy (CP). STUDY DESIGN: A population-based case-control study was conducted using Washington State birth certificate data linked to hospital discharge data. Cases (688) were children 相似文献   

Weight gain and spontaneous preterm birth: the role of race or ethnicity and previous preterm birth

OBJECTIVE: To study how the relationship between gestational weight gain and spontaneous preterm birth interacts with maternal race or ethnicity and previous preterm birth status. METHODS: This was a retrospective cohort study of singleton births to women of normal or low prepregnancy body mass index. Gestational weight gain was measured as total weight gain divided by weeks of gestation at delivery, and weight gain was categorized as low (less than 0.27 kg/wk,), normal (0.27-0.52 kg/wk), or high (more than 0.52 kg/wk). Univariable and multivariable analyses were performed on the relationship between weight gain categories and spontaneous preterm birth, stratified by maternal race or ethnicity and history of previous preterm birth. RESULTS: Overall, low weight gain was associated with spontaneous preterm birth (adjusted odds ratio [AOR] 2.5, 95% confidence interval [CI] 2.0-3.1). Although low gain was consistently associated with increased spontaneous preterm birth, some differences were found in subgroup analysis. Among African Americans with a previous preterm birth, both low and high weight gain were associated with increased odds of spontaneous preterm birth (AOR for low weight gain 4.3, 95% CI 1.2-15.5; AOR for high weight gain 6.1, 95% CI 1.8-20.2). For all other groups, high weight gain was not associated with spontaneous preterm birth. Among Asians with a previous preterm birth, low weight gain was not statistically significantly associated with spontaneous preterm birth (AOR 1.9, 95% CI 0.5-7.7). Among Asians there was also a non-statistically significant inverse relationship between high weight gain and spontaneous preterm birth (AOR 0.5, 95% CI 0.3-1.1). CONCLUSION: These results confirm an association between low maternal weight gain and spontaneous preterm birth. The effect modification of maternal race or ethnicity and history of previous preterm birth on this association deserves further study. LEVEL OF EVIDENCE: II-2.     

The impact of interpregnancy interval and previous preterm birth on the subsequent risk of preterm birth

OBJECTIVE: To examine the impact of the interpregnancy interval and a previous preterm birth on the subsequent risk of a preterm birth. METHODS: A retrospective analysis was conducted on a group of 4072 women who had at least two consecutive births, excluding multiple gestation, fetal anomalies, cervical incompetence, and stillbirth. Multivariate logistic regression was used to investigate the association between interpregnancy interval, preterm birth of the first child in the pair (index pregnancy), and the risk of a preterm birth of the second child in the pair (outcome pregnancy). RESULTS: Women with interpregnancy intervals of less than 12 months (odds ratio [OR] 1.3; 95% confidence interval [CI] 1.0-1.7) were at increased risks of preterm birth with the outcome pregnancy. Furthermore, there was an increased risk for a subsequent preterm birth in women who had a preterm birth in the index pregnancy (OR 4.2; 95% CI 3.0-6.0). The risk decreased as the interpregnancy interval increased, with a relatively low risk at 18 to 48 months; subsequently, it increased sharply. In contrast, women who had delivered their previous infants at term carried an increased risk of preterm birth with the outcome pregnancy only if the interval was less than 6 months. CONCLUSION: A difference was found in the impact of the interpregnancy interval on the subsequent risk of preterm birth between women with a prior preterm birth and those who previously delivered an infant at term.     

Pregnancy-induced hypertension is associated with lower infant mortality in preterm singletons

OBJECTIVE: To assess the association between pregnancy-induced hypertension (PIH) and infant mortality. DESIGN: Retrospective cohort study. SETTING: Birth and infant death registration dataset of the USA. POPULATION: A total of 17,432,987 eligible, liveborn singleton births in 1995-2000. METHODS: Multivariate logistic regression was applied to evaluate the association between PIH and infant mortality, with adjustment of potential confounders. MAIN OUTCOME MEASURES: Infant death (0-364 days) and its three components: early neonatal death (0-6 days), late neonatal death (7-27 days), and postneonatal death (28-364 days). RESULTS: There was a significant reduction in infant mortality associated with PIH in early preterm infants (OR = 0.59, 95% CI: 0.56-0.63) and in late preterm infants (OR = 0.80, 95% CI: 0.73-0.87), but a significant increase in term infants (OR = 1.08, 95% CI: 1.02-1.14). Both in early preterm and late preterm births, early neonatal mortality (OR = 0.38, 95% CI: 0.34-0.42; OR = 0.68, 95% CI: 0.61-0.77) and late neonatal mortality (OR = 0.59, 95% CI: 0.50-0.70; OR = 0.76, 95% CI: 0.61-0.96) were decreased in infants born to mothers with PIH compared with those born to mothers with normal blood pressure. The PIH-associated reduction in neonatal mortality among preterm singletons was stronger in small-for-gestational-age infants than in normal growth infants and stronger in infants born to nulliparous women than in those born to multiparous women. CONCLUSIONS: PIH is associated with lower risk of infant death in preterm births but higher risk in term births.     

Estimated effect of 17 alpha-hydroxyprogesterone caproate on preterm birth in the United States

OBJECTIVE: A multicenter, randomized placebo-controlled trial among women with singleton pregnancies and a history of spontaneous preterm birth found that weekly injections of 17 alpha-hydroxyprogesterone caproate (17P), initiated between 16 and 20 weeks of gestation, reduced preterm birth by 33%. The current study estimated both preterm birth recurrence and the potential reduction in the national preterm birth rate. METHODS: Using 2002 national birth certificate data, augmented by vital statistics from 2 states, we estimated the number of singleton births delivered to women eligible for 17P through both a history of spontaneous preterm birth and prenatal care onset within the first 4 months of pregnancy. The number and rate of recurrent spontaneous preterm births were estimated. To predict effect, the reported 33% reduction in spontaneous preterm birth attributed to 17P therapy was applied to these estimates. RESULTS: In 2002, approximately 30,000 recurrent preterm births occurred to women eligible for 17P, having had a recurrent preterm birth rate of 22.5%. If 17P therapy were delivered to these women, nearly 10,000 spontaneous preterm births would have been prevented, thereby reducing the overall United States preterm birth rate by approximately 2%, from 12.1% to 11.8% (P < .001), with higher reductions in targeted groups of eligible pregnant women. CONCLUSION: Use of 17P could reduce preterm birth among eligible women, but would likely have a modest effect on the national preterm birth rate. Additional research is urgently needed to identify other populations who might benefit from 17P, evaluate new methods for early detection of women at risk, and develop additional prevention strategies. LEVEL OF EVIDENCE: III.     

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.     

Is a poor pregnancy outcome related to young maternal age? A study of teenagers in Estonia during the period of major socio-economic changes (from 1992 to 2002)

OBJECTIVE: To assess the risk of low birth weight, preterm birth, stillbirth, neonatal and postneonatal death among primiparous teenagers having singleton births, compared to a similar group of women aged 20-24 years in Estonia during the period of major socio-economic changes. STUDY DESIGN: Registry study using the data from the Estonian Medical Birth Registry (EMBR) for years 1992-2002; EMBR data were linked with infant deaths in the Estonian Mortality Database. Study population included 51,890 women aged 13-24 years, arranged into three groups: < or =17, 18-19, and 20-24. Crude odds ratios (OR), adjusted ORs and their 95% confidence intervals (CI) for the different outcomes were estimated using multiple logistic regression analysis. RESULTS: Compared with women aged 20-24 years, the risk of low birth weight and preterm birth was higher among teenagers. The risk of low birth weight and preterm birth within the study group as a whole did not change during the study period. Increased risks in neonatal and postneonatal death among younger teenagers of an age of 17 years and less seem to be a result of prematurity. CONCLUSIONS: Despite major socio-economic changes resulting in improvements in obstetric care and growth in incomes, teenagers remained a higher risk group.     

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.     

Maternal Hypertension and Spontaneous Preterm Births Among Black Women

Objective: To examine effects of maternal hypertension on spontaneous preterm birth (birth at less than 37 weeks’ gestation) among black women.Methods: Using hospital discharge summary records from the National Hospital Discharge Survey between 1988 and 1993, we conducted a case-control study to assess the risk of spontaneous preterm birth among black women with chronic hypertension preceding pregnancy and pregnancy-induced hypertension. Logistic regression was used to derive odds ratios (ORs) and 95% confidence intervals (CIs).Results: Preterm births were almost two times more likely for women with pregnancy-induced hypertension (OR = 1.8; 95% CI, 1.5, 2.2), more than 1.5 times more likely for women with chronic hypertension preceding pregnancy (OR = 1.6; 95% CI, 1.3, 2.1), and more than four times more likely for women with pregnancy-aggravated hypertension (OR = 4.4; 95% CI, 2.9, 6.7) compared with normotensive women. Preterm births also were associated significantly with antepartum hemorrhage, poor fetal growth, marital status, and source of payment. The odds of preterm birth by maternal hypertension were increased among women with chronic hypertension and genitourinary infection, whereas the odds of preterm birth were reduced among women with pregnancy-induced hypertension and genitourinary infection.Conclusion: These findings are important in demonstrating the relation between type of hypertension in pregnancy and preterm birth. The relationships between maternal hypertension and preterm birth need to be further investigated to provide some guidelines in the management of hypertension in pregnancy and assessment of prenatal care compliance for black women, particularly when genitourinary infection is present.     

Recurrence of fetal growth restriction in singleton and twin gestations

Objective.?Patterns of recurrence of restricted fetal growth provide important insights to understand the relative contributions of genetic versus environmental influences. Although there is evidence of increased tendency of small for gestational age (SGA) births to recur, whether similar patterns of recurrence in twins among women that delivered a prior singleton SGA birth remains poorly studied.

Methods.?We used Missouri's maternally-linked data (1978–1997), and restricted the analysis to women that delivered their first two consecutive live births. SGA (birthweight <10th and <5th centile for gestational age) recurrence was examined in two distinct analyses: women that delivered their first two singleton live births (n = 305,654) and those that delivered their first singleton live birth followed by twin live births (n = 8594). Sib–sib pairwise odds ratio (pOR) were estimated from bivariate logistic regression with robust variance estimation after adjustments for confounders.

Results.?Risks of SGA were 24.3% and 6.1% in the second singleton birth among women with and without a previous singleton SGA, respectively (pOR 3.9, 95% CI 3.7–4.0). The corresponding risks among twins with and without a previous singleton SGA birth were 16.9% and 6.7%, respectively (pOR 2.3, 95% CI 1.8–2.8). In the singleton–singleton cohort, the highest recurrence risk for SGA occurred around the same gestational age window as the first singleton SGA birth. These associations were stronger for more severe forms of SGA (<5th centile).

Conclusions.?The likelihood of SGA to recur within sibships is strong, with varying magnitude of risks between singleton–singleton and singleton–twin births.     

Spontaneous preterm birth of liveborn infants in women at low risk in Australia over 10 years: a population-based study

Objectives  To describe a 10-year trend in preterm birth.
Design  Population-based study.
Setting  Australia.
Population  All women who gave birth during 1994–03.
Methods  The proportion of spontaneous preterm births (greater than or equal to 22 weeks of gestation and less than 37 completed weeks of gestation) was calculated by dividing the number of women who had a live spontaneous preterm birth (excluding elective caesarean section and induction of labour) by the total number of women who had a live birth after spontaneous onset of labour (excluding elective caesarean section and induction of labour). This method was repeated for the selected population of women at low risk.
Main outcome measure  Preterm birth rates among the overall population of women; preterm birth among all women with a spontaneous onset of labour; and preterm birth in a selected population of women who were either primiparous or multiparous, non-Indigenous; aged 20–40 years and who gave birth to a live singleton baby after the spontaneous onset of labour.
Results  Over the 10-year study period, the proportion of all women having a live preterm birth in Australia increased by 12.1% (from 5.9% in 1994 to 6.6% in 2003). Among women with a spontaneous onset of labour, there was an increase of 18.3% (from 5.7 to 6.7%). Among the selected population of low-risk women after the spontaneous onset of labour, the rate increased by 10.7% (from 5.6 to 6.2%) among first time mothers and by 19.2% (4.4–5.2%) among selected multiparous women.
Conclusions  Over the 10-year period of 1994–03, the rate of spontaneous preterm birth among low-risk women having a live singleton birth has risen in Australia.     

Second-trimester cervical ultrasound: associations with increased risk for recurrent early spontaneous delivery

OBJECTIVE: To determine whether short cervical length or internal os funneling before 20 weeks' gestation predicts early preterm birth or pregnancy loss in women with at least one prior spontaneous early preterm birth. METHODS: Transvaginal cervical ultrasound examinations were done every 2 weeks on 69 women with singleton gestations and histories of at least one prior spontaneous birth between 16 and 30 weeks' gestation. The results of those examinations were correlated with gestational age at delivery. RESULTS: Among 53 women who had ultrasound examinations before 20 weeks' gestation, those with cervical lengths at or below the tenth percentile for the study population (22 mm, n = 4) or funneling of the internal os (n = 5) were more likely than women without those factors to have spontaneous preterm births within 2 weeks (33% versus 0%, P = .01) or 4 weeks from the ultrasound examination (67% versus 0%, P < .001) or before 35 weeks' gestation (100% versus 19%, P < .001). Short cervical length or funneling between 20-24 and 25-29 weeks was also associated with increased risk of spontaneous preterm birth before 35 weeks' gestation (P < or = .05 and P = .002, respectively) but not with increased risk of spontaneous preterm birth within 2 or 4 weeks of ultrasound examination. CONCLUSION: Women with prior early spontaneous preterm births who have short cervical lengths or funneling of the internal cervical os before 20 weeks' gestation are at increased risk of subsequent spontaneous preterm birth.     

Cervical dimensions and risk of preterm birth: a prospective cohort study

OBJECTIVE: To examine the relation between cervical dilatation and length and the risk of spontaneous preterm birth, including its subtypes preterm labor and preterm premature rupture of membranes (PROM). METHODS: Cervical dimensions assessed by clinical examination were recorded prospectively at 24-29 weeks' gestation in 871 subjects with singleton pregnancies who were followed to delivery. Relative risks (RRs) of preterm birth, preterm labor, and preterm PROM were calculated for clinically distinguishable categories of cervical dilatation and length and for cervical score (length minus dilatation). Regression analysis was used to adjust for confounding. Time to delivery from baseline examination was summarized using survival analysis. RESULTS: There were 73 spontaneous preterm births (8.3%), 46 preterm labors and 27 cases of preterm PROM. All cervical measurements were associated with increased risks of preterm birth, with increasing abnormality more strongly predictive of risk. The adjusted RR for preterm birth with dilatation of at least 0.5 cm was 2.9 (95% confidence interval [CI] 1.2, 7.3); for length of 1.5 cm or less, the RR was 2.1 (95% CI 1.0, 4.5), and for cervical score less than 2.0, the RR was 2.8 (95% CI 1.4, 5.6). The association with cervical measurements was stronger for preterm PROM than for preterm labor, although precision was limited. These measurements had high specificity (93-99%) and low sensitivity (8-20%) for predicting preterm birth. CONCLUSION: In asymptomatic women at 24-29 weeks' gestation, greater cervical dilatation and shorter length were associated with increased risk of spontaneous preterm delivery, particularly preterm PROM.     

Population‐Based Study of Cesarean Section After In Vitro Fertilization in Australia

Abstract: Background: Decisions about method of birth should be evidence based. In Australia, the rising rate of cesarean section has not been limited to births after spontaneous conception. This study aimed to investigate cesarean section among women giving birth after in vitro fertilization (IVF). Methods: Retrospective population‐based study was conducted using national registry data on IVF treatment. The study included 17,019 women who underwent IVF treatment during 2003 to 2005 and a national comparison population of women who gave birth in Australia. The outcome measure was cesarean section. Results: Crude rate of cesarean section was 50.1 percent versus 28.9 percent for all other births. Single embryo transfer was associated with the lowest (40.7%) rate of cesarean section. Donor status and twin gestation were associated with significantly higher rates of cesarean section (autologous, 49.0% vs donor, 74.9%; AOR: 2.20, 95% CI: 1.80, 2.69) and (singleton, 45.0% vs twin gestations, 75.7%; AOR: 3.81, 95% CI: 3.46, 4.20). The gestation‐specific rate (60.1%) of cesarean section peaked at 38 weeks for singleton term pregnancies. Compared with other women, cesarean section rates for assisted reproductive technology term singletons (27.8% vs 43.8%, OR: 2.02 [95% CI: 1.95–2.10]) and twins (62.0% vs 75.7%, OR: 1.92 [95% CI: 1.74–2.11]) were significantly higher. Conclusions: Rates for cesarean section appear to be disproportionately high in term singleton births after assisted reproductive technology. Vaginal birth should be supported and the indications for cesarean section evidence based. (BIRTH 37:3 September 2010)