Medically indicated preterm birth: recognizing the importance of the problem

Preeclampsia mediates the association between shorter height and increased risk of preterm delivery

Background

Maternal short stature has been observed to increase the risk of preterm birth; however, the aetiology behind this phenomenon is unknown. We investigated whether preeclampsia, an obstetric complication that often leads to preterm delivery and is reported to have an inverse association with women’s height, mediates this association.

Methods

We studied 218 412 women with no underlying diseases before pregnancy, who delivered singletons from 2005 to 2011 and were included in the Japan Society of Obstetrics and Gynecology perinatal database, which is a national multi-centre-based delivery database among tertiary hospitals. We assessed the risk of preterm delivery in relation to height using multivariate analysis, and how the association was mediated by risk of preeclampsia using mediation analysis.

Results

Each 5-cm decrement in height was associated with significantly higher risk of preterm delivery [relative risk 1.20; 95% confidence interval (CI): 1.13, 1.27] and shorter gestational age (−0.30; 95% CI: −0.44, −0.16 weeks). Mediation analysis showed that the effect of shorter height on increased risk of preterm delivery, due to an indirect effect mediated through increased risk of preeclampsia, was substantial for shorter gestational age (48%), as well as risk of preterm delivery (28%). When examining the three subtypes of preterm delivery separately, mediated effect was largest for provider-initiated preterm delivery without premature rupture of membranes (PROM) (34%), compared with spontaneous preterm delivery without PROM (17%) or preterm delivery with PROM (0%).

Conclusions

Preeclampsia partially mediates the association between maternal short stature and preterm delivery.

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.

An elevated amniotic fluid prostaglandin F2α concentration is associated with intra-amniotic inflammation/infection, and clinical and histologic chorioamnionitis, as well as impending preterm delivery in patients with preterm labor and intact membranes

OBJECTIVE

To determine whether an elevated amniotic fluid concentration of prostaglandin F2α (PGF2α) is associated with intra-amniotic inflammation/infection and adverse pregnancy outcomes in patients with preterm labor and intact membranes.

MATERIALS AND METHODS

The retrospective cohort study included 132 patients who had singleton pregnancies with preterm labor (< 35 weeks of gestation) and intact membranes. Amniotic fluid was cultured for aerobic and anaerobic bacteria as well as for genital mycoplasmas. Intra-amniotic inflammation was defined by an elevated amniotic fluid matrix metalloproteinase-8 (MMP-8) concentration (>23 ng/mL). PGF2α was measured with a sensitive and specific immunoassay. The amniotic fluid PGF2α concentration was considered elevated when it was above the 95th percentile among pregnant women at 15-36 weeks of gestation who were not in labor (≥170 pg/mL).

RESULTS

(1) The prevalence of an elevated amniotic fluid PGF2α concentration was 40.2% (53/132) in patients with preterm labor and intact membranes; (2) patients with an elevated amniotic fluid PGF2α concentration had a significantly higher rate of positive amniotic fluid culture [19% (10/53) versus 5% (4/79); p = 0.019], intra-amniotic inflammation/infection [49% (26/53) versus 20% (16/79); p = 0.001], spontaneous preterm delivery, clinical and histologic chorioamnionitis, and funisitis, as well as a higher median amniotic fluid MMP-8 concentration and amniotic fluid white blood cell count and a shorter amniocentesis-to-delivery interval than those without an elevated concentration of amniotic fluid PGF2α (p < 0.05 for each); and (3) an elevated amniotic fluid PGF2α concentration was associated with a shorter amniocentesis-to-delivery interval after adjustment for the presence of intra-amniotic inflammation/infection [hazard ratio 2.1, 95% confidence interval (CI) 1.4-3.1; p = 0.001].

CONCLUSION

The concentration of PGF2α was elevated in the amniotic fluid of 40.2% of patients with preterm labor and intact membranes and is an independent risk factor for intra-amniotic inflammation/infection, impending preterm delivery, chorioamnionitis, and funisitis.

Circadian clock-related genetic risk scores and risk of placental abruption

INTRODUCTION

The circadian clock plays an important role in several aspects of female reproductive biology. Evidence linking circadian clock-related genes to pregnancy outcomes has been inconsistent. We sought to examine whether variations in single nucleotide polymorphisms (SNPs) of circadian clock genes are associated with PA risk.

METHODS

Maternal blood samples were collected from 470 PA case and 473 controls. Genotyping was performed using the Illumina Cardio-MetaboChip platform. We examined 119 SNPs in 13 candidate genes known to control circadian rhythms (e.g., CRY2, ARNTL, and RORA). Univariate and penalized logistic regression models were fit to estimate odds ratios (ORs); and the combined effect of multiple SNPs on PA risk was estimated using a weighted genetic risk score (wGRS).

RESULTS

A common SNP in the RORA gene (rs2899663) was associated with a 21% reduced odds of PA (P < 0.05). The odds of PA increased with increasing wGRS (Ptrend < 0.001). The corresponding ORs were 1.00, 1.83, 2.81 and 5.13 across wGRS quartiles. Participants in the highest wGRS quartile had a 5.13-fold (95% confidence interval: 3.21-8.21) higher odds of PA compared to those in the lowest quartile. Although the test for interaction was not significant, the odds of PA was substantially elevated for preeclamptics with the highest wGRS quartile (OR = 14.44, 95%CI: 6.62-31.53) compared to normotensive women in the lowest wGRS quartile.

DISCUSSION

Genetic variants in circadian rhythm genes may be associated with PA risk. Larger studies are needed to corroborate these findings and to further elucidate the pathogenesis of this important obstetrical complication.

Maternal hypertension after a low-birth-weight delivery differs by race/ethnicity: evidence from the National Health and Nutrition Examination Survey (NHANES) 1999-2006

Studies have suggested an increase in maternal morbidity and mortality due to cardiovascular diseases in women with a prior low-birth-weight (LBW, <2,500 grams) delivery. This study evaluated blood pressure and hypertension in women who reported a prior preterm or small-for-gestational-age (SGA) LBW delivery in the National Health and Nutrition Examination Survey 1999-2006 (n = 6,307). This study also aimed to explore if race/ethnicity, menopause status, and years since last pregnancy modified the above associations. A total of 3,239 white, 1,350 black, and 1,718 Hispanics were assessed. Linear regression models were used to evaluate blood pressure by birth characteristics (preterm-LBW, SGA-LBW, and birthweight ≥2,500). Logistic regression models estimated the odds ratios (OR) of hypertension among women who reported a preterm-LBW or SGA-LBW delivery compared with women who reported an infant with birthweight ≥2,500 at delivery. Overall, there was a positive association between a preterm-LBW delivery and hypertension (adjusted OR = 1.39, 95% confidence interval (CI) 1.02-1.90). Prior SGA-LBW also increased the odds of hypertension, but the estimate did not reach statistical significance (adjusted OR = 1.21, 95% CI 0.76-1.92). Race/ethnicity modified the above associations. Only black women had increased risk of hypertension following SGA-LBW delivery (adjusted OR = 2.09, 95% CI 1.12-3.90). Black women were at marginally increased risk of hypertension after delivery of a preterm-LBW (adjusted OR = 1.49, 95% CI 0.93-2.38). Whites and Hispanics had increased, but not statistically significant, risk of hypertension after a preterm-LBW (whites: adjusted OR = 1.39, 95% CI 0.92-2.10; Hispanics: adjusted OR = 1.22, 95% CI 0.62-2.38). Stratified analysis indicated that the associations were stronger among women who were premenopausal and whose last pregnancy were more recent. The current study suggests that in a representative United States population, women with a history of preterm- or SGA-LBW deliveries have increased odds of hypertension and this risk appears to be higher for black women and younger women.

Preterm subtypes by immigrants' length of residence in Norway: a population-based study

Background

The reduction of the preterm delivery (PTD) rate is a maternal and child health target. Elevated rates have been found among several immigrant groups, but few studies have distinguished between PTD according to the mode of birth start. In addition, migrants’ birth outcomes have further been shown to be affected by the time in residence; however, the association to PTD subtypes has not previously been assessed. In this study we examined if the risk of spontaneous and non-spontaneous, or iatrogenic, PTD among immigrants in Norway varied according to the length of residence and the country of birth, and compared with the risks among the majority population.

Methods

We linked population-based birth and immigration data for 40 709 singletons born to immigrant women from Iraq, Pakistan, the Philippines, Somalia, Sri Lanka and Vietnam and 868 832 singletons born to non-immigrant women from 1990–2009. Associations between the length of residence and subtypes of PTD were estimated as relative risks (RRs) with 95% confidence intervals (CIs) from multivariable models.

Results

In total, 48 191 preterm births occurred. Both spontaneous and non-spontaneous PTD rates were higher among immigrants (4.8% and 2.0%) than among non-immigrants (3.6% and 1.6%). Only non-spontaneous PTD was associated with longer lengths of residence (p trend <0.001). Recent immigrants (<5 years of residence) and non-immigrants had a similar risk of non-spontaneous PTD, whereas immigrants with lengths of residence of 5–9 years, 10–14 years and ≥15 years had adjusted RRs of 1.18 [95% CI 1.03,1.35], 1.43 [95% CI 1.20,1.71] and 1.66 [95% CI 1.41,1.96]. The association was reduced after further adjustments for maternal and infant morbidity. Conversely, the risk of spontaneous PTD among immigrants was not mitigated by length of residence, but varied with country of birth according to the duration of pregnancy in term births.

Conclusions

Non-spontaneous PTD increased with the length of residence whereas spontaneous PTD remained elevated regardless of the length of residence. Policies to improve birth outcomes in ethnically mixed populations should address the modifiable causes of PTD rather than aiming to reduce absolute PTD rates.

Siglec-5 and Siglec-14 are polymorphic paired receptors that modulate neutrophil and amnion signaling responses to group B Streptococcus

Siglec-5 and Siglec-14 are shown to be paired inhibitory/activating receptors expressed on neutrophils and amniotic epithelium and modulating immune responses to group B Streptococcus.

Group B Streptococcus (GBS) causes invasive infections in human newborns. We recently showed that the GBS β-protein attenuates innate immune responses by binding to sialic acid–binding immunoglobulin-like lectin 5 (Siglec-5), an inhibitory receptor on phagocytes. Interestingly, neutrophils and monocytes also express Siglec-14, which has a ligand-binding domain almost identical to Siglec-5 but signals via an activating motif, raising the possibility that these are paired Siglec receptors that balance immune responses to pathogens. Here we show that β-protein–expressing GBS binds to both Siglec-5 and Siglec-14 on neutrophils and that the latter engagement counteracts pathogen-induced host immune suppression by activating p38 mitogen-activated protein kinase (MAPK) and AKT signaling pathways. Siglec-14 is absent from some humans because of a SIGLEC14-null polymorphism, and homozygous SIGLEC14-null neutrophils are more susceptible to GBS immune subversion. Finally, we report an unexpected human-specific expression of Siglec-5 and Siglec-14 on amniotic epithelium, the site of initial contact of invading GBS with the fetus. GBS amnion immune activation was likewise influenced by the SIGLEC14-null polymorphism. We provide initial evidence that the polymorphism could influence the risk of prematurity among human fetuses of mothers colonized with GBS. This first functionally proven example of a paired receptor system in the Siglec family has multiple implications for regulation of host immunity.

Ischemic placental disease and risks of perinatal mortality and morbidity and neurodevelopmental outcomes

Preeclampsia, intrauterine growth restriction, and placental abruption are serious obstetrical complications that constitute the syndrome of ischemic placental disease and account for a disproportionate degree of perinatal morbidity and mortality. We review the risks of stillbirth and neonatal and infant mortality in relation to ischemic placental disease, focusing on population-based studies. We also review the risks of neonatal morbidity and neurodevelopmental outcomes in relation to ischemic placental disease. A synthesis of the findings of the relevant studies relating ischemic placental disease to adverse perinatal outcomes underscores two important observations. First, despite the low prevalence of each of the three obstetrical complications, all are associated with increased risks of adverse perinatal and infant outcomes, as well as neurodevelopmental deficits. Second, the burden of increased perinatal risks appears strongest during the preterm period. Efforts to reduce the risks of ischemic placental disease remain critically important and developing effective clinical interventions will be a target worthy for consideration.

Long-term maternal morbidity and mortality associated with ischemic placental disease

Ischemic placental disease can have long-term maternal health implications. In this article, we discuss the three conditions of ischemic placental disease (preeclampsia, fetal growth restriction, and abruption placenta) and its associated long-term maternal morbidity. Retrospective observational studies comparing pregnancies complicated by ischemic placental disease to uncomplicated pregnancies suggest an increased long-term risk of hypertension, cardiovascular death, metabolic syndrome, and cerebrovascular disease. This association is much stronger in women who had an indicated-preterm delivery due to ischemic placental disease. It is important to adequately counsel women who are diagnosed with these conditions about their future health risks. Increased awareness of the potential health risks and multidisciplinary collaboration remains paramount to instituting the appropriate screening and preventative strategies (i.e., behavior modification) for affected women.

Prediction and prevention of ischemic placental disease

Preeclampsia, intrauterine growth restriction (IUGR), and placental abruption are obstetrical conditions that constitute the syndrome of ischemic placental disease or IPD, the leading cause of indicated preterm birth and an important cause of neonatal morbidity and mortality. While the phenotypic manifestations vary significantly for preeclampsia, IUGR, and abruption, these conditions may share a common underlying etiology as evidenced by: (1) shared clinical risk factors, (2) increased recurrence risk across pregnancies as well as increased co-occurrence of IPD conditions within a pregnancy, and (3) findings that suggest the underlying pathophysiologic processes may be similar. IPD is of major clinical importance and accounts for a large proportion of indicated preterm delivery ranging from the periviable to late preterm period. Successful prevention of IPD and resultant preterm delivery could substantially improve neonatal and maternal outcomes. This article will review the following topics: (1) The complicated research literature on aspirin and the prevention of preeclampsia and IUGR. (2) Research evidence on other medical interventions to prevent IPD. (3) New clinical interventions currently under investigations, including statins. (4) Current clinical recommendations for prevention of ischemic placental disease.

Antidepressant use and risk for preeclampsia

BACKGROUND

Prior studies suggest that women who use antidepressants during pregnancy have an increased risk for preeclampsia, yet the comparative safety of specific antidepressants remains unclear. US nationwide Medicaid Analytic eXtract (MAX) data have not been used to study medication safety during pregnancy.

METHODS

We identified 100,942 pregnant women with depression from 2000 to 2007 MAX data. We used pharmacy dispensing records to ascertain exposure to selective serotonin reuptake inhibitor (SSRI), serotonin-norepenephrine reuptake inhibitor (SNRI), tricyclic, bupropion, other antidepressant monotherapy or polytherapy, and specific antidepressants, during the second trimester and first half of the third trimester. Relative risks (RRs) and 95% confidence intervals (CIs) were adjusted for delivery year, preeclampsia risk factors, depression severity proxies, other antidepressant indications, other medications, and healthcare utilization.

RESULTS

The risk of preeclampsia was 5.4% among women with depression and no antidepressant exposure. Compared with these women, the risk for preeclampsia was higher among those receiving SNRI (RR: 1.52, 95% CI = 1.26-1.83) and tricyclic monotherapy (RR: 1.62, 95% CI = 1.23-2.12), but not SSRI monotherapy (RR: 1.00, 95% CI = 0.93-1.07) or other antidepressants. Compared with women receiving SSRI monotherapy, preeclampsia risk was higher among women with SNRI (RR: 1.54, 95% CI = 1.28-1.86) and tricyclic (RR: 1.64, 95% CI = 1.25-2.16) monotherapy. None of the specific SSRIs was associated with preeclampsia. The RR with venlafaxine was 1.57 (95% CI = 1.29-1.91) and with amitriptyline 1.72 (95% CI = 1.24-2.40).

CONCLUSIONS

In this population, SNRIs and tricyclics were associated with a higher risk of preeclampsia than SSRIs.

Obstetrical interventions for term first deliveries in the US

BACKGROUND

Labour induction and caesarean are increasingly done without clinical indication. However, little is known about the prevalence of such interventions, or the characteristics of women who receive them. We used the 2003 revision of the US birth certificates to summarise recorded interventions and to characterise maternal profiles associated with such interventions.

METHODS

We carried out a retrospective study of 2.35 million primiparous women delivering singleton live births at 37-44 weeks in the US from 2005 to 2008. We used the 2003 revision of the birth certificate to define delivery categories: 'indicated' were those with induced labour or pre-labour caesarean for hypertension, diabetes, chorioamnionitis, failed cephalic version at ≥40 weeks, growth restriction (<3rd centile), or post-term (≥42 weeks); those with pre-labour caesarean with breech at ≥39 weeks; or those with caesarean with labour lasting ≥12 h, failed trial of labour, vacuum/forceps extraction, or fetal intolerance to labour. Remaining deliveries with induction/caesarean were classified as 'non-indicated' and all other deliveries 'spontaneous'.

RESULTS

Half of all term first births (50%) were delivered after intervention, and half of interventions were non-indicated (26% of all deliveries). Women with interventions were more likely to deliver on a weekday. Non-indicated interventions were more common among socially advantaged women.

CONCLUSIONS

Nearly a quarter of US term first deliveries had an indicated intervention, and another quarter received intervention without a recorded clinical indication. Both numbers are probably underestimates.

Subtypes of preterm birth and the risk of postneonatal death

OBJECTIVE

To examine the differences in postneonatal death risk among 3 clinical subtypes of preterm birth: preterm premature rupture of membranes (PROM), indicated preterm birth, and spontaneous preterm labor.

STUDY DESIGN

We analyzed the 2001-2005 US linked birth/infant death (birth cohort) datasets. The preterm birth subtypes were classified using information on the birth certificate: reported PROM, induction of labor, cesarean section, and complications of pregnancy and labor. Cox proportional hazard models were used to estimate covariate-adjusted hazard ratios and 95% CIs for postneonatal death (from days 28 to 365). Estimation was given for preterm birth subtypes in a week-by-week analysis. Causes of death were analyzed by preterm birth subtype and then separately at 24-27, 28-31, and 32-36 weeks of gestation.

RESULTS

For the total of 1895350 singleton preterm births who survived the neonatal period, the postneonatal mortality rate was 1.11% for preterm PROM, 0.78% for indicated preterm birth, and 0.53% for spontaneous preterm labor. Preterm PROM was associated with significantly higher risk of postneonatal death compared with spontaneous preterm labor in infants born at 27 weeks gestation or later. Similarly, indicated preterm birth was associated with a significantly higher risk of postneonatal death than spontaneous preterm labor in infants born at 25 weeks gestation or later. Preterm PROM and indicated preterm birth were associated with greater risk of death in the postneonatal period compared with spontaneous preterm labor, irrespective of the cause of death.

CONCLUSION

Subtypes of preterm birth carry different risks of postneonatal mortality. Prevention of preterm-related postneonatal death may require more research into the root causes of preterm birth subtypes.

Associations of LINE-1 DNA Methylation with Preterm Birth in a Prospective Cohort Study

Preterm birth affects over 12% of all infants born in the US yet the biology of early delivery remains unclear, including whether epigenetic mechanisms are involved. We examined associations of maternal and umbilical cord blood long interspersed nuclear element-1 (LINE-1) DNA methylation with length of gestation and odds of preterm birth in singleton pregnancies in Project Viva. In white blood cells from maternal blood during 1(st) trimester (n=914) and 2(nd) trimester (n=922), and from venous cord blood at delivery (n=557), we measured LINE-1 by pyrosequencing (expressed as %5 methyl cytosines within the LINE-1 region analyzed [%5mC]). We ran linear regression models to analyze differences in gestation length, and logistic models for odds of preterm birth (<37 v. ≥37 weeks gestation), across quartiles of LINE-1. Mean(SD) LINE-1 levels were 84.3(0.6), 84.5(0.4), and 84.6(0.7) %5mC for 1(st) trimester, 2(nd) trimester and cord blood, respectively. Mean(SD) gestational age was 39.5(1.8) weeks, and 6.5% of infants were born preterm. After adjustment for maternal age, race/ethnicity, BMI, education, smoking status, and fetal sex, women with the highest vs. lowest quartile of 1(st) trimester LINE-1 had longer gestations (0.45 weeks [95% CI 0.12, 0.78]) and lower odds of preterm birth (OR 0.40 [0.17, 0.94]), whereas associations with cord blood LINE-1 were in the opposite direction (-0.45 weeks, -0.83, -0.08) and (OR 4.55 [1.18, 17.5]). In conclusion, higher early pregnancy LINE-1 predicts lower risk of preterm birth. In contrast, preterm birth is associated with lower LINE-1 in cord blood.

The preterm birth syndrome: issues to consider in creating a classification system

A comprehensive classification system for preterm birth requires expanded gestational boundaries that recognize the early origins of preterm parturition and emphasize fetal maturity over fetal age. Exclusion of stillbirths, pregnancy terminations, and multifetal gestations prevents comprehensive consideration of the potential causes and presentations of preterm birth. Any step in parturition (cervical softening and ripening, decidual-membrane activation, and/or myometrial contractions) may initiate preterm parturition, and should be recorded for every preterm birth, as should the condition of the mother, fetus, newborn, and placenta, before a phenotype is assigned.

Are maternal genitourinary infection and pre-eclampsia associated with ADHD in school-aged children?

OBJECTIVE

To investigate the hypothesis that maternal genitourinary infection (GU) infection is associated with increased risk of ADHD.

METHOD

The authors obtained linked Medicaid billing data for pregnant women and their children in South Carolina, with births from 1996 through 2002 and follow-up data through 2008. Maternal GU infections and pre-eclampsia were identified on the basis of diagnoses made during pregnancy, and cases of ADHD were identified on the basis of diagnoses made in the child's Medicaid file.

RESULTS

There were 84,721 children in the data set used for analyses. Maternal genitourinary infection was associated with significantly increased odds of ADHD (OR = 1.29, 95% CI = 1.23-1.35). Pre-eclampsia was also associated with increased risk (OR = 1.19, 95% CI = 1.07-1.32). Children whose mothers had both GU infection and pre-eclampsia were 53% more likely to have ADHD, compared to those with neither exposure. When we examined specific infection diagnoses, chlamydia/nongonococcal urethritis, trichomoniasis, urinary tract infection, and candidiasis were associated with increased risk of ADHD, whereas gonorrhea was not.

DISCUSSION

Maternal GU infection appeared to be associated with increased risk of ADHD, and based on the findings it was concluded that further research is needed to describe the mechanism(s) underlying the association.

Association between maternal comorbidity and preterm birth by severity and clinical subtype: retrospective cohort study

Background

Preterm birth (PTB) is a major cause of infant morbidity and mortality, but the relationship between comorbidity and PTB by clinical subtype and severity of gestational age remains poorly understood. We evaluated associations between maternal comorbidities and PTB by clinical subtype and gestational age.

Methods

We conducted a retrospective cohort study of 1,329,737 singleton births delivered in hospitals in the province of Québec, Canada, 1989-2006. PTB was classified by clinical subtype (medically indicated, preterm premature rupture of membranes (PPROM), spontaneous preterm labour) and gestational age (< 28, 28-31, 32-36 completed weeks). Odds ratios (OR) of PTB by clinical subtype for systemic and localized maternal comorbidities were estimated using polytomous logistic regression, adjusting for maternal age, grand multiparity, and period. Attributable fractions were calculated.

Results

PTB rates were higher among mothers with comorbidity (10.9%) compared to those without comorbidity (4.7%). Several comorbidities were associated with greater odds of medically indicated PTB compared with no comorbidity, but only comorbidities localized to the reproductive system were associated with spontaneous PTB. Drug dependence and mental disorders were strongly associated with PPROM and spontaneous PTBs across all gestational ages (OR > 2.0). At the population level, several major comorbidities (placental abruption, chorioamnionitis, oliogohydramnios, structural abnormality, cervical incompetence) were key contributors to all clinical subtypes of PTB, especially at < 32 weeks. Major systemic comorbidities (preeclampsia, anemia) were key contributors to PPROM and medically indicated PTBs.

Conclusions

The relationship between comorbidity and clinical subtypes of PTB depends on gestational age. Prevention of PPROM and spontaneous PTB may benefit from greater attention to preeclampsia, anemia and comorbidities localized to the reproductive system.

Disturbed sleep, a novel risk factor for preterm birth?

OBJECTIVE

The etiology of preterm birth (PTB) is likely caused by multiple factors, which may include disturbed sleep. We evaluated whether sleep disturbance was associated with PTB and whether the association was affected by other psychosocial risk factors.

METHODS

Pregnant women (n=217) for whom we had depression and sleep data at 20 or 30 weeks gestation and delivery information were evaluated. Logistic models were used to test the hypotheses that disturbed sleep was associated with PTB.

RESULTS

Time in bed at 20 weeks was significantly associated with risk for preterm delivery (odds ratio [OR] 1.43, 95% confidence interval [CI] 1.08-1.88). However, after controlling for depression/selective serotonin reuptake inhibitors (SSRI) status, history of PTB, age, employment, and marital status, this relationship was no longer significant (OR 1.26, 95% CI .92-1.71). No other relationships were significant.

CONCLUSIONS

We report preliminary evidence suggesting that poor sleep may contribute to risk for PTB. Although it is speculative and additional work is needed to confirm or refute whether sleep is an independent or mediating risk factor for PTB, disturbed sleep does appear to play a role in adverse pregnancy outcomes.

Medically indicated--iatrogenic prematurity

Premature delivery of an infant is occasionally performed because of complications of pregnancy. This article reviews common medical indications for preterm delivery and the available evidence supporting delivery before 37 weeks of gestation. In many conditions, few data exist to guide optimal timing of delivery and management is guided by expert opinion. Ultimately, an individual assessment must be made in each case to weigh the risks that pregnancy continuation poses to the mother and/or fetus with the risks of prematurity and its associated morbidities.

Trends in cesarean delivery at preterm gestation and association with perinatal mortality

OBJECTIVE

We sought to examine the extent to which a temporal increase in preterm cesarean delivery is associated with gestational age-specific changes in perinatal survival in preterm gestations.

STUDY DESIGN

We utilized data on singleton births in the United States (1990 through 2004) delivered between 24-36 weeks' gestation. Associations between changes in cesarean delivery at preterm gestations and trends in the risk of preterm stillbirth, and neonatal and perinatal mortality were estimated before and after adjustments for a variety of potential confounders.

RESULTS

From 1990 through 2004, cesarean delivery rates increased by 50.6%, 40.7%, and 35.8% at 24-27, 28-33, and 34-36 weeks, respectively. The largest incremental effect of cesarean was associated with a reduction in stillbirths by 5.8%, 14.2%, and 23.1% at 24-27, 28-33, and 34-36 weeks, respectively, leading to an 11.4%, 4.9%, and 0.6% reduction in perinatal deaths at 24-27, 28-33, and 34-36 weeks, respectively.

CONCLUSION

Increasing rates of preterm cesarean were associated with improved perinatal survival. This association was evident largely because of dramatic incremental declines in stillbirths.

Uncovering the complex relationship between pre-eclampsia, preterm birth and cerebral palsy

Pre-eclampsia is a leading cause of preterm birth, which is strongly associated with cerebral palsy (CP). However, there is controversy about whether pre-eclampsia is associated with increased risk of CP. We evaluated the association between pre-eclampsia and CP in 122,476 mother-child pairs insured by the South Carolina Medicaid programme, with births between 1996 and 2002. Prenatal billing records were linked to the children's Medicaid billing records after birth until December 2008. The odds of CP were modelled using logistic regression with generalised estimating equations. There were 337 children (0.28%) diagnosed with CP by at least two different health care providers, and 4226 (3.5%) women were diagnosed with pre-eclampsia at least twice during pregnancy. Children whose mothers had pre-eclampsia were almost twice as likely to have CP compared with children of mothers without pre-eclampsia [odds ratio (OR)=1.94, 95% confidence interval (CI) 1.25, 2.97]. The association was only significant for pre-eclampsia diagnosed prior to 37 weeks' gestation. Full term (gestational age ≥ 37 weeks) infants whose mothers were diagnosed with pre-eclampsia prior to 37 weeks had increased odds of CP compared with full term children whose mothers did not have pre-eclampsia (OR=3.41, 95% CI 1.40, 8.31). Preterm infants whose mothers had pre-eclampsia were at significantly increased risk of CP compared with full term infants whose mothers did not have pre-eclampsia (OR=5.88, 95% CI 3.40, 10.17). The greatest risk for CP was in preterm infants whose mothers did not have pre-eclampsia (OR=8.12, 95% CI 6.49, 10.17 compared with full term infants without exposure to pre-eclampsia). We conclude that pre-eclampsia with onset before 37 weeks' gestation is a significant risk factor for CP. Some of the association is probably attributable to high risk of preterm birth because of early pre-eclampsia, while a 'direct' effect of pre-eclampsia on fetal brain development also seems likely.

Maternal pre-eclampsia is associated with childhood epilepsy in South Carolina children insured by Medicaid

OBJECTIVE

We examined the association between maternal pre-eclampsia/eclampsia (PE) and childhood epilepsy.

METHODS

We conducted a retrospective cohort study using linked maternal-child billing data for Medicaid births in South Carolina from 1996 through 2002, with follow-up billing data for children through December 2008. Women with PE (exposed) and children with epilepsy (outcome) were identified using ICD-9 codes. Non-singleton births, children with documented conditions known to cause abnormal brain development, and children who neither remained in Medicaid until age 6 nor were diagnosed with epilepsy were excluded.

RESULTS

Of 95,450 mother-child pairs in the final cohort, 5460 mothers were diagnosed with PE (5.7%) and 1106 children had the outcome of epilepsy (1.2%). After controlling for potential confounders, PE was significantly associated with risk of epilepsy (OR=1.46, 95% CI=1.17-1.82). The increased risk of epilepsy was observed only among full-term infants, and for this subgroup, late PE (first diagnosed after 37 weeks of gestation) was significantly associated with epilepsy (OR=1.61, 95% CI=1.21-2.16). The association between PE and epilepsy was particularly strong for children with focal epilepsy.

CONCLUSION

Pre-eclampsia is associated with childhood epilepsy. Additional research is needed to identify potential mechanisms for the association.

Midpregnancy levels of angiogenic markers in relation to maternal characteristics

OBJECTIVE

The purpose of this study was to describe relations among maternal demographic and lifestyle characteristics and midpregnancy levels of angiogenic markers (soluble Fms-like tyrosine kinase-1, placental growth factor, soluble endoglin).

STUDY DESIGN

In a large pregnancy cohort, linear models were used to evaluate relations among maternal characteristics and midpregnancy angiogenic markers with and without covariate adjustment. Associations were examined in a subcohort that included term and preterm deliveries (n = 1302) and among "normal" term pregnancies (n = 668).

RESULTS

Concentrations of all factors declined with increasing maternal body mass index. Multiparous women had lower soluble Fms-like tyrosine kinase-1 levels than primiparous women. Higher placental growth factor and slightly lower soluble endoglin levels were observed among women who smoked at enrollment, but not among those women who quit before enrollment. African American women had higher levels of all markers.

CONCLUSION

Understanding relations among maternal characteristics and levels of angiogenic factors may improve studies that use these markers to examine etiology and/or to predict adverse pregnancy outcome.

Ischemic placental disease: maternal versus fetal clinical presentations by gestational age

OBJECTIVE

Preeclampsia, small for gestational age (SGA), and abruption are considered ischemic placental diseases (IPD), and are major contributors to both maternal and fetal morbidity and mortality. Although the placenta is considered a fetal organ, these conditions can present clinically with either maternal or fetal manifestations, but their relationship to preterm births is largely unexplored.

METHODS

We designed a population-based study to assess the origins of IPD. IPD was classified as maternal (preeclampsia only), fetal (SGA only), or both (abruption only, preeclampsia with either SGA or abruption, or all 3). The study was based on 90,500 women that delivered singleton live births at 22-44 weeks gestation.

RESULTS

Among 77,275 term births with IPD, 23.2% presented as maternal disease only, 68.9% as fetal disease, and 7.9% as both. In contrast, among 12,906 preterm births with IPD, the proportions were roughly equal (maternal 32.9%, fetal 36.5%, and both 30.6%). Among spontaneous preterm births with IPD, a greater proportion had a fetal presentation (43.0%), whereas among indicated preterm births with IPD, a greater proportion (43.4%) had both maternal and fetal presentations.

CONCLUSIONS

IPD at preterm gestations is more likely to involve both the mother and fetus than at term. The differing clinical presentations by gestational age suggest different pathways between term and preterm births. This may reflect heterogeneous processes for IPD at early vs. late gestations, regardless of the effects of differing gestational age thresholds for interventions.

Reproductive outcomes among male and female workers at an aluminum smelter

OBJECTIVES

Several adverse pregnancy outcomes were reported among female laboratory workers in a North American aluminum smelter. To determine whether these outcomes were associated with any occupational exposure at the plant, a cross-sectional survey was undertaken.

METHODS

Rates of miscarriage, premature singleton birth, and major congenital anomaly occurring during employment were compared with a reference group comprised of all pregnancies that occurred before employment.

RESULTS

Among female workers, the excess of congenital anomalies among female laboratory workers that defined the initial cluster was observed, but no specific pattern was found.

CONCLUSIONS

On the basis of these analyses, the increase in congenital anomalies could not be attributed to occupational exposures at the smelter nor could potential exposure likely explain the diverse anomalies described.

Heterogeneity of preterm birth subtypes in relation to neonatal death

OBJECTIVE

To investigate the heterogeneity of preterm labor, preterm premature rupture of membranes (PROM), and indicated preterm birth in overall and gestational-age-specific neonatal death risk.

METHODS

We used 2001 U.S. linked birth/infant death (birth cohort) data sets for this analysis. We categorized three preterm birth subtypes according to reported preterm PROM, induction of labor, cesarean delivery, and pregnancy and labor complications. We used Cox proportional hazard models to calculate covariates adjusted hazard ratios (HRs) for neonatal death (0-27 days of life) among preterm neonates born at 24-27, 28-31, 32-33, and 34-36 weeks of gestation, with preterm labor being the referent.

RESULTS

There were 3,763,306 singleton live births at 24-44 weeks of gestation in the data set. Preterm PROM, indicated preterm birth, and preterm labor had neonatal death risk of 2.7%, 1.8%, and 1.1%, respectively. Compared with preterm labor, preterm PROM had shorter gestational age and lower birth weight, so did indicated preterm birth but to a lesser extent. Preterm PROM and indicated preterm birth after 28 weeks of gestation were associated with higher neonatal death risk than preterm labor. At 34-36 weeks of gestation, the HR of preterm PROM was 1.53 (95% confidence interval 1.20-1.95), and the HR of indicated preterm birth was 2.06 (95% confidence interval 1.83-2.33). The increased risk from preterm PROM and indicated preterm birth was not limited to early neonatal death in the first 7 days.

CONCLUSION

Preterm PROM and indicated preterm birth had higher risk of neonatal death than preterm labor, indicating heterogeneity in gestational age distribution and gestational-age-specific neonatal death risk.

LEVEL OF EVIDENCE

II.

Distinguishing pathological from constitutional small for gestational age births in population-based studies

BACKGROUND

Small for gestational age (SGA) can occur following a pathological process or may represent constitutionally small fetuses. However, distinguishing these processes is often difficult, especially in large studies, where the term SGA is often used as a proxy for restricted fetal growth. Since biologic variation in fetal size is largely a third trimester phenomenon, we hypothesized that the definition of SGA at term may include a sizeable proportion of constitutionally small fetuses. In contrast, since biologic variation in fetal size is not fully expressed in (early) preterm gestations, it is plausible that SGA in early preterm gestations would comprise a large proportion of growth restricted fetuses.

AIM

We compared mortality and morbidity rates between SGA and appropriate for gestational age (AGA) babies.

SUBJECTS

A population-based study of over 19million non-malformed, singleton births (1995-04) in the United States was performed. Gestational age (24-44weeks) was based on a clinical estimate. SGA and AGA were defined as sex-specific birthweight <10th and 25-74th centiles, respectively, for gestational age. All analyses were adjusted for a variety of confounding factors.

OUTCOME MEASURES

Excess mortality risk in SGA and AGA babies.

RESULTS

On an additive scale, stillbirth and neonatal mortality rates were higher at every preterm gestation among SGA than AGA births, and similar at term gestations. An inverse relationship between gestational age and excess deaths between SGA and AGA babies delivered at <37weeks was evident.

CONCLUSIONS

In early preterm gestations, the definition of SGA may well be justified as a proxy for IUGR. In contrast, SGA babies that are delivered at term are likely to be constitutionally small.

The challenge of infant mortality: have we reached a plateau?

OBJECTIVES

Infant mortality is a major indicator of the health of a nation. We analyzed recent patterns and trends in U.S. infant mortality, with an emphasis on two of the greatest challenges: (1) persistent racial and ethnic disparities and (2) the impact of preterm and low birthweight delivery.

METHODS

Data from the national linked birth/infant death datasets were used to compute infant mortality rates per 100,000 live births by cause of death (COD), and per 1,000 live births for all other variables. Infant mortality rates and other measures of infant health were analyzed and compared. Leading and preterm-related CODs, and international comparisons of infant mortality rates were also examined.

RESULTS

Despite the rapid decline in infant mortality during the 20th century, the U.S. infant mortality rate did not decline from 2000 to 2005, and declined only marginally in 2006. Racial and ethnic disparities in infant mortality have persisted and increased, as have the percentages of preterm and low birthweight deliveries. After decades of improvement, the infant mortality rate for very low birthweight infants remained unchanged from 2000 to 2005. Infant mortality rates from congenital malformations and sudden infant death syndrome declined; however, rates for preterm-related CODs increased. The U.S. international ranking in infant mortality fell from 12th place in 1960 to 30th place in 2005.

CONCLUSIONS

Infant mortality is a complex and multifactorial problem that has proved resistant to intervention efforts. Continued increases in preterm and low birthweight delivery present major challenges to further improvement in the infant mortality rate.

Maternal depressive symptoms, depression, and psychiatric medication use in relation to risk of preterm delivery

PURPOSE

This study examined the associations among maternal depression, measured in several ways, psychiatric medication use in pregnancy, and preterm delivery (PTD).

METHODS

Data were collected from 3,019 women enrolled in the Pregnancy Outcomes and Community Health Study (1998-2004), a prospective study of pregnant women in five Michigan communities. Information on depressive symptoms, history of depression, and psychiatric medication use was ascertained through interviews at mid-pregnancy. These variables and other relevant covariates were incorporated into regression models with a binary outcome, that is, term (> or =37 weeks' gestation) as referent and PTD (<37 weeks' gestation). A second set of models used a multicategory outcome, namely, term as the referent and PTD further subdivided by gestational weeks and clinical circumstances.

MAIN FINDINGS

The odds of overall PTD was increased among women who used psychiatric medication during pregnancy and had either elevated levels of depressive symptoms at mid-pregnancy (adjusted odds ratio [AOR], 2.0; 95% confidence interval [CI], 1.1-3.6) or a history of depression before pregnancy (AOR, 1.6; 95% CI, 1.1-2.5). The combination of psychiatric medication use in pregnancy and depression, before pregnancy, or within pregnancy was most strongly linked to a medically indicated delivery before 35 weeks' gestation (AOR, 2.9 and 3.6, respectively).

CONCLUSIONS

There are at least two plausible explanations for these findings. First, psychiatric medication use in pregnancy may pose an excess risk of PTD. Second, medication use may be an indicator of depressive symptom severity, which is a direct or indirect (i.e., alters behavior) contributing factor to PTD.

[Algorithm for an etiological classification of prematurity]

The etiology of preterm birth is difficult to classify. It is usually divided into three clinical types according to its clinical presentation: medically indicated; caused by ruptured membranes; and spontaneous or idiopathic. However, this classification is controversial, imprecise and can result in multiple interpretations when applied.

OBJECTIVE

To design an etiologically based classification of preterm birth, and to design a system to easily assign each case during the perinatal period.

METHODS

Review of literature, qualitative analysis using consensus methods through nominal group technique, and quantitative analysis of a pilot study using a first version of the algorithm.

RESULTS

A classification is made to establish a general division between the "primary cause" and "associated causes" of preterm birth, that allows remote causes or risk factors to be included. The primary cause includes seven categories: inflammatory (ruptured membranes and related); vascular (intrauterine growth restriction and related); maternal-local; maternal-systemic; fetal pathology; fetal distress; idiopathic. The medically indicated preterm birth is defined as a previous or independent category and so is compatible with the other, previously mentioned causes . An algorithm was designed to make it easier to classify the primary cause of preterm birth using a flowchart.

CONCLUSIONS

A pragmatic classification of preterm birth is proposed that may help to achieve better precision and agreement between clinicians.

[Late preterm infants: A population at underestimated risk]

BACKGROUND AND OBJECTIVE

There has been a gradual rise in prematurity rates recent years, almost exclusively at the expense of the late preterm (34 to 36 weeks). This population, although with less risk than smaller preterm gestational age, has a morbidity rate significantly higher than term infants. However, there is some underestimation regarding developments in the short and long term. The aim of this study was to look at the incidence of prematurity in our institution and to analyze morbidity and mortality in late preterm compared with term infants

SUBJECTS AND METHODS

We performed a retrospective review of newborns in our Hospital from January 1992 until December 31, 2008. Late preterm group was defined as between 34(0/7) and 36(6/7) weeks gestation (N=2003) and term infants from 37 to 42 weeks gestation (N=32015). We formed 2 subgroups according two time periods (1992-1998 and 2000-2008). The morbidity and mortality for each of the groups and subgroups, and the morbidity from week 34 to 42, were analysed and compared.

RESULTS

During the period studied, the prematurity rate increased from 3.9% to 9.8%, exclusively at the expense of the late preterm (79%). The rate of mortality in late preterm was 5 per thousand compared to 1.1 per thousand in the term (P <0.0001, OR 4.71, 95% CI 2.3-9.5). The incidence of admission to the Neonatal Unit, Cesarean rate, twin, respiratory disorders, need for respiratory support in the form of nasal CPAP or mechanical ventilation, incidence of apnea, jaundice requiring phototherapy, hypoglycaemia and need for parenteral nutrition were significantly higher (P<0.0001) in the late preterm group compared with term infants. The morbidity rate decreased significantly as gestational age increased, with the lowest value from 39 weeks.

CONCLUSIONS

Morbidity and mortality in late preterm infants is significantly higher than in term infants. The guidelines for these near term premature babies need to be reviewed, looking for possible causes of prematurity, and trying to reduce their impact, as well as developing a protocol for their care and close monitoring to minimize the associated morbidity. There should be long-term monitoring to find out the consequences on their psychomotor development. The obstetrics group should be made aware of the true risks of births in the near-term gestational ages.

Goals and strategies for prevention of preterm birth: an obstetric perspective

Complications of prematurity surpass congenital malformations as the leading cause of infant mortality in the United States. Since 1990, there has been a steady rise in preterm birth, alarming health professionals from all disciplines. This review from a prenatal perspective confirms those concerns and describes the risks and opportunities that may attend efforts to improve the health of fetuses, newborns, and infants. Fetal and live-born outcomes are included.