Modelling sequence of prior pregnancies on subsequent risk of very preterm birth

Watson LF, Rayner J‐A, King J, Jolley D, Forster D, Lumley J. Modelling sequence of prior pregnancies on subsequent risk of very preterm birth. Paediatric and Perinatal Epidemiology 2010. The prevalence and intractability of preterm birth is known as is its association with reproductive history, but the relationship with sequence of pregnancies is not well studied. The data were from a population‐based case–control study, conducted in Victoria, Australia. The study recruited women giving birth between April 2002 and April 2004 from 73 maternity hospitals. Detailed reproductive histories were collected by interview a few weeks after the birth. The cases were 603 women having a singleton birth between 20 and <32 weeks gestation (very preterm births including terminations of pregnancy). The controls were 796 randomly selected women from the population having a singleton birth of at least 37 completed weeks gestation. Unconditional logistic regression was used to assess the association of very preterm birth with sequence of pregnancies defined by their outcome (prior abortion – spontaneous or induced, and prior preterm or term birth) with adjustment for sociodemographic factors. The outcomes of each prior pregnancy, stratified by pregnancy order, and starting with the pregnancy immediately before the index or control pregnancy, were categorised as one of abortion, preterm birth or term birth. We showed that each of these prior pregnancy events was an independent risk of very preterm birth. This finding does not support the hypothesis of a neutralising effect of a term birth after an abortion on the subsequent risk for very preterm birth and is further evidence for the cumulative or increasing risk associated with increasing numbers of prior abortions or preterm births.     

Induced abortion: not an independent risk factor for pregnancy outcome, but a challenge for health counseling

PURPOSE: Low birth weight (LBW), preterm births, abnormal placentation, and miscarriages have been associated with prior induced abortions. An incidence-related effect has been suggested. The objective of this study is to assess the effects of prior induced abortions on obstetric risk factors and pregnancy outcome in conditions of free high-standard maternity care used by almost the entire pregnant population in Finland. METHODS: We analyzed a population-based database including 26,976 singleton pregnancies from 1989 to 2001, of which 2364 were among women with one prior induced abortion and 355 women had had at least two prior induced abortions. Data included maternal risk factors, pregnancy characteristics, and obstetric outcome measures and were based on results of a self-administered questionnaire at 20 weeks of pregnancy and clinical records. Odds ratios (ORs) concerning pregnancy outcomes were calculated in multiple logistic regression analysis. RESULTS: Induced abortions were associated with several known pregnancy risk factors; specifically, maternal age older than 35 years, unemployment, unmarried status, low educational level, smoking, alcohol consumption, overweight condition, and chronic illnesses. Preterm birth (OR, 1.19; 95% confidence interval, 1.01-1.41) in women with one prior abortion (7.3% versus 6.2%) and LBW (OR, 1.54; 95% confidence interval, 1.02-2.32) in women with two or more prior abortions (7.0% versus 4.7%) appeared to be more common, but after logistic regression analysis, we found no evidence of adverse pregnancy outcomes. CONCLUSIONS: Induced abortion is not an independent risk factor for adverse obstetric outcome. Marked health behavioral pregnancy risks are associated with prior induced abortions. Health counseling of these women is a challenge, but this objective has not yet been achieved.     

Social differences of very preterm birth in Europe: interaction with obstetric history. Europop Group.

Social differences of very preterm birth (22-32 completed weeks of amenorrhea) were studied using data from a large case-control survey in Europe between 1994 and 1997; 1,675 very preterm births and 7,965 full-term births were included. The relation between social factors and very preterm birth was studied according to obstetric history and the mode of delivery onset. Very preterm birth was significantly related to low educational level among women with no previous adverse pregnancy outcome (odds ratio (OR) = 2.67, 95 percent confidence interval (CI) 1.66-4.28) and among primigravid women and those with previous first-trimester abortion (OR = 2.01, 95 percent CI 1.56-2.58). In this group, unemployment of all household members was associated with a double risk of very preterm birth. No significant association between very preterm birth and socioeconomic status was observed among women with previous second-trimester abortion or preterm birth. Socioeconomic indicators remained significantly associated with both spontaneous and induced very preterm births among women with no previous late fetal loss or preterm birth. The results are consistent with social factors affecting the risk of very preterm birth, but the relation differs according to obstetric history.     

Large social disparities in spontaneous preterm birth rates in transitional Russia

OBJECTIVE: This study estimated the effect of maternal sociodemographic, obstetric and lifestyle factors on the risk of spontaneous preterm birth in a Russian town. METHODS: All women with singleton pregnancies registered at prenatal care centres in Severodvinsk in 1999 comprised the cohort for this study (n=1559). Analysis was based on spontaneous live singleton births at the maternity home (n=1103). Multivariable logistic regression was applied to quantify the effect of the studied factors on the risk of preterm birth. Differences in gestation duration were studied using multiple linear regression. RESULTS: In total, 5.6% of all spontaneous births were preterm. Increased risks of preterm delivery were found in women with lower levels of education and in students. Placental complications, stress and a history of fetal death in previous pregnancies were also associated with elevated risks for preterm delivery. Smoking, hypertension and multigravidity were associated with reduced length of pregnancy in metric form. CONCLUSION: In addition to medical risk factors, social factors are important determinants of preterm birth in transitional Russia. Large disparities in preterm birth rates may reflect the level of inequalities in transitional Russia. Social variations in pregnancy outcomes should be monitored.     

Characteristics of women with recurrent spontaneous abortions and women with favorable reproductive histories.

Women with a history of recurrent spontaneous abortions (repeaters) are compared with women who have had live births and no spontaneous abortions (multiparae) and women who have had live births and only one spontaneous abortion (sporadics) to identify characteristics of the women and their abortuses that might predict subsequent fetal loss. A number of risk factors for recurrent spontaneous abortion have been identified: the loss of a chromosomally normal conception, loss after the first trimester of pregnancy, a delay in conceiving prior to the study pregnancy, a diagnosis of cervical incompetence, and a history of very low birthweight deliveries. The odds ratios associated with being a repeater vary from 1.4 to 5.6 depending on the number of characteristics present.     

Delayed childbearing: no evidence for increased risk of low birth weight and preterm delivery

Prior studies of the effect of increased maternal age on reproductive outcome in primiparous women have often ignored the possible influence on this relation of more frequent histories of spontaneous abortion and infertility in older women. When these histories are taken into account, the present study of 1,382 white primiparous women who had live singleton deliveries at Yale-New Haven Hospital finds no evidence for an increased risk of low birth weight (relative risk (RR) = 1.06, 95% confidence interval (CI) = 0.38-2.94) or preterm delivery (RR = 1.07, 95% CI = 0.50-2.24) in women delivering at age 30 years or more compared with younger women. Mean birth weight (beta = -19 g, p = 0.57) and gestational age (beta = -0.16 weeks, p = 0.34) were also not significantly affected by older maternal primiparity. Women aged 35 years or more had twice the rate of preterm births compared with women under age 30, although this result was not statistically significant in this data set (RR = 2.07, 95% CI = 0.67-6.35). Other confounding variables were taken into account.     

Evaluation of antenatal risk scoring in a preterm birth prevention and perinatal loss

The study aim was to determine risk factors associated with preterm delivery, perinatal mortality, and neonatal morbidity among 687 indigent, pregnant women in their first term registered with the New Civil Hospital, Ahmedabad, India, between September, 1989, and March, 1991. Women were scored according to their level of risk: no risk, mild risk, moderate risk, and severe risk, from scores based on sociodemographic and obstetric data: pallor, maternal weight, 2 or more prior abortions, first pregnancy or 5 pregnancies, adolescent pregnancy, prior preterm birth, prior prenatal mortality or stillbirths. Out of 696 deliveries, there were 71 (10.2%) preterm births, of which 3 (2.38%) were among women within the no risk groups. There were 47 (11.10%) from the mild risk group and 20 (14.08%) from the moderate risk group. There were 20% from the severe risk group. Perinatal mortality was 84.77/1000 births, and 7.94 among the no risk group. The perinatal mortality rate rose with level of risk, with 92.20 per thousand births for the mild risks to 200 for the severe risks, which was statistically significant. Neonatal morbidity also increased with the increased level of risk. Preterm birth was found not to be associated with pallor and prior history of stillbirth. Perinatal mortality was not associated with pallor and first pregnancy. Factors significantly associated with preterm births and perinatal mortality were maternal malnutrition, higher pregnancy order, older maternal age at delivery, and prior preterm births and fetal loss. Pregnant women with risk factors had greater relative risk of preterm birth and perinatal mortality by 5.01 and 13.09 times. With maternal risk factors, the risk increased by 80.05% and 92.35%. The risk factors were highly sensitive for preterm births (95.77%), but had low specificity (19.69%), and low positive predictive value (11.93%). Perinatal mortality sensitivity, specificity, and positive predictive values were 98.31%, 19.90%, and 10.34%n respectively. The findings differed from previously reported studies; scoring system used has a higher sensitivity to predicting preterm birth and perinatal mortality among high risk women, and poor sensitivity among low risk women. Moderate and mild could be identified with this system and referred for follow-up.     

Predictors of vaginal bleeding during the first two trimesters of pregnancy

This study evaluates maternal age, race, cigarette smoking, prior spontaneous abortion, prior induced abortion, and prior preterm birth in relation to vaginal bleeding during the first two trimesters of pregnancy. Information on vaginal bleeding and predictors came from the Pregnancy, Infection, and Nutrition Study, which enrolled 2806 pregnant women at 24-29 weeks' gestation during 1995-2000 in central North Carolina, USA. Generalised estimating equations were applied to take into account repeated episodes of vaginal bleeding during pregnancy. Women with advanced maternal age and passive smoking exposure were more likely to experience more intense vaginal bleeding during pregnancy, as were women with prior preterm birth. More intense bleeding was also more likely to be reported among women with multiple prior spontaneous abortions or multiple prior induced abortions, but not among women with a single prior spontaneous or induced abortion. The combination of prior spontaneous and induced abortion showed a dose-response association with the occurrence of vaginal bleeding during pregnancy.     

17-α hydroxyprogesterone caproate for the prevention of preterm birth

17?α hydroxyprogesterone caproate is a synthetic form of the natural progestin 17-α hydroxyprogesterone that is US FDA approved for the prevention of recurrent spontaneous preterm birth in women with a history of a prior singleton preterm birth. For women with a history of a prior spontaneous preterm birth between 20 weeks and 36 weeks and 6 days of gestation, the use of 17-α hydroxyprogesterone caproate has been shown to reduce the risk of recurrent preterm birth by more than 30%. This medication is the only drug currently FDA approved for the prevention of preterm birth, and it is the first drug the FDA has approved for use exclusively during pregnancy in approximately 15 years.     

Induced abortion and low birthweight in the following pregnancy

BACKGROUND: To examine whether induced abortion increases the risk of low birthweight in subsequent singleton live births. METHODS: Cohort study using the Danish Medical Birth Registry (MBR), the Hospital Discharge Registry (HDR), and the Induced Abortion Registry (IAR). All women who had their first pregnancy during 1980-1982 were identified in the MBR, the HDR, and the IAR. We included all 15,727 women whose pregnancy was terminated by a first trimester induced abortion in the induced abortion cohort and 46,026 women whose pregnancy was not terminated by an induced abortion were selected for the control cohort. All subsequent pregnancies until 1994 were identified by register record linkage. RESULTS: Low birthweight (<2500 g) in singleton term live births occurred more frequently in women with one, two, three or more previous induced abortions, compared with women without any previous induced abortion of similar gravidity, 2.2% versus 1.5%, 2.4% versus 1.7%, and 1.8% versus 1.6%, respectively. Adjusting for maternal age and residence at time of pregnancy, interpregnancy interval, gender of newborn, number of previous spontaneous abortions and number of previous low birthweight infants (control cohort only), the odds ratios (OR) of low birthweight in singleton term live births in women with one, two or more previous first trimester induced abortions were 1.9 (95% CI: 1.6, 2.3), and 1.9 (95% CI: 1.3, 2.7), respectively, compared with the control cohort of similar gravidity. High risks were mainly seen in women with an interpregnancy interval of more than 6 months. CONCLUSIONS: The findings suggest a positive association between one or more first trimester induced abortions and the risk of low birthweight in subsequent singleton term live births when the interpregnancy interval is longer than 6 months. This result was unexpected and confounding cannot be ruled out.     

Singleton Preterm Birth: Risk Factors and Association with Assisted Reproductive Technology

The objectives of this study were to determine risk factors for early (less than 34 weeks gestation) and late (34–36 weeks gestation) preterm singleton birth, by assisted reproductive technology (ART) status. We linked data from Massachusetts birth records and ART records representing singleton live births from 1997 through 2004. Using multinomial regression models, we assessed risk factors for early and late preterm birth by ART status. From 1997 to 2004 in Massachusetts, among non-ART births, risk factors for early and late preterm birth were similar and included women <15 and ≥35 years of age, those of non-white race or Hispanic ethnicity, those with ≤12 years of education, those with chronic diabetes, those with gestational diabetes, those with gestational hypertension, those who smoked during pregnancy, those who used fertility medications, and those who had not had a previous live birth. Among ART births, risk factors for early and late preterm birth differed and odds of early preterm birth were increased among women with ≤12 years of education while odds of late preterm birth were increased among women with gestational diabetes. Odds of both early and late preterm birth were increased among women of non-white race or Hispanic ethnicity and among women with gestational hypertension. Among non-ART births, increased risk for preterm birth was more strongly related to socioeconomic factors than among ART births. Medical conditions were associated with an increased risk for preterm birth regardless of women’s ART status. Efforts to prevent preterm births should focus on reducing modifiable risk factors.     

Previous abortion and the risk of low birth weight and preterm births

OBJECTIVE: To investigate the association between previous abortion and low birth weight (LBW) and preterm birth (PB). METHOD: The study examined live, singleton births using data from the United States Collaborative Perinatal Project. Logistic regression was used to control for obstetric and medical history, and lifestyle and demographic factors. RESULT: Compared with women with no history of abortion, women who had one, two and three or more previous abortions were 2.8 (95% CI 2.48 to 3.07), 4.6 (95% CI 3.94 to 5.46) and 9.5 (95% CI 7.72 to 11.67) times more likely to have LBW, respectively. The risk for PB was also 1.7 (95% CI 1.52 to 1.83), 2.0 (95% CI 1.73 to 2.37) and 3.0 (95% CI 2.47 to 3.70) times higher for women with a history of one, two and three or more previous abortions, respectively. CONCLUSION: Previous abortion is a significant risk factor for LBW and PB, and the risk increases with the increasing number of previous abortions. Practitioners should consider previous abortion as a risk factor for LBW and PB.     

Influence of smoking and snuff cessation on risk of preterm birth

The mechanisms by which antenatal smoking exposure increases the risk of preterm birth remain unknown. Swedish oral moist snuff contains quantities of nicotine comparable to those typically absorbed from cigarette smoking, but does not result in exposure to the products of combustion, for example carbon monoxide. In a nation-wide study of 776,836 live singleton births in Sweden from 1999 to 2009, the authors used multiple logistic regression models to examine associations between cessation of smoking and Swedish snuff use early in pregnancy and risk of preterm birth (before 37 weeks). Compared with non-tobacco users both before and in early pregnancy, the adjusted odds ratios (OR), 95% confidence interval (CI) were OR=0.92, 95% CI 0.84-1.01, for women who stopped using snuff, and OR=0.90, 95% CI 0.87-0.94, for women who stopped smoking. In contrast, continued snuff use and smoking were associated with increased risks of preterm birth (adjusted OR=1.29, 95% CI 1.17-1.43, adjusted OR=1.30, 95% CI 1.25-1.36, respectively). The snuff and smoking-related risks were, if anything, higher for very (before 32 weeks) than moderately (32-36 weeks) preterm birth, and also higher for spontaneous than induced preterm birth. These findings suggest that antenatal exposure to nicotine is involved in the mechanism by which tobacco use increase the risk of preterm birth.     

The influence of maternal age on very preterm birth of twins: differential effects by parity

For singleton births, parity can modify the effect of maternal age on birth outcomes such as low birthweight and preterm birth; however, it is unknown whether this relationship exists for twin births. As the rate of twin births increases among older women, it is important to understand how parity may influence the relationship between maternal age and adverse birth outcomes. The NCHS Matched Multiple Birth Data Set, which contains all twin births in the USA from 1995 to 1998, was analysed. Parity was grouped into two levels (primiparous--no prior live births, and multiparous--at least one prior live birth), and maternal age was divided into the following groups: 20-24, 25-29, 30-34, 35-39, and 40 years or more. Very preterm birth was defined as births occurring before 33 weeks. Logistic regression was used to obtain odds ratios (OR) to estimate the risk of very preterm birth, and to determine the relationships between parity, maternal age, and very preterm birth. Among primiparae, women 40 years and older had a reduced risk of very preterm birth compared with women of 25-29 years (OR 0.74 [95% CI=0.66, 0.84]). Among multiparae, women 40 years and older had the same risk of very preterm birth compared with women of 25-29 years (OR 1.00 [95% CI=0.90, 1.12]). However, stratification by education revealed that the age gradient was limited to women with >12 years education among primiparae. The effect of maternal age on very preterm birth of twins differs according to parity. To some extent, that effect is further modified by education. Therefore, future analyses of maternal age and twin birth outcomes should account for measures of obstetric history and other factors, which may influence these results.     

Ectopic pregnancy and prior induced abortion.

We compared the prior pregnancy histories of 85 multigravid women with an ectopic pregnancy and 498 multigravid delivery comparison subjects. We found a relationship between the number of prior induced abortions and the risk of ectopic pregnancy: the crude relative risk of ectopic pregnancy was 1.6 for women with one prior induced abortion and 4.0 for women with two or more prior induced abortions; however, use of multivariate techniques to control confounding factors reduced the relative risks to 1.3 (95 per cent confidence interval, 0.6-2.7) and 2.6 (95 per cent confidence interval, 0.9-7.4), respectively. The analysis suggests that induced abortion may be one of several risk factors for ectopic pregnancy, particularly for women who have had abortions plus pelvic inflammatory disease or multiple abortions.     

Socio-economic factors associated with preterm delivery. Results of the European project in Spain

Objectives: The objectives of this paper were to analyse the effect of social, personal and medical risk factors on preterm birth (moderate versus very preterm) or on two preterm birth groups (spontaneous versus indicated).Methods: Results from the Spanish collaborating centre of the European multicentre case-control study EUROPOP (European Program of Occupational Risks and Pregnancy Outcome) are presented. All preterm births (529) between 22 and 36 completed weeks of amenorrhea and 788 births of 37 or more completed weeks of amenorrhea (control group) are included. Explicative variables are divided in social, personal and medical factors. A univariate and multivariate analysis by means of a logistic regression were carried out.Results: Very preterm birth risk was higher for women over 34 years, adjusted OR: 2.53 (1.42-4.52), with lower educational level, adjusted OR: 1.79 (1.07-2.98), for primigravid women or multigravid women with only first trimestre abortion, adjusted OR: 1.86 (1.13-3.04), and for multigravid women with previous preterm birth or second trimestre abortion, adjusted OR: 5.53 (2.97-10.35). A similar trend was observed for moderate preterm birth. Probability of spontaneous preterm birth was higher for mother over 34 years, adjusted OR: 1.51 (1.01-2.26), with lower income, adjusted OR: 1.75 (1.07-2.88) and for multigravid women with previous preterm birth or second trimestre abortion, adjusted OR: 2.96 (1.86-4.71). Results were similar for indicated preterm birth.Conclusion.: Social differences were found to be related to moderate and very preterm birth. No differences were observed between risk factors and kind of preterm birth: spontaneous or indicated.     

Pregnancy and safety outcomes in women vaccinated with an AS03-adjuvanted split virion H1N1 (2009) pandemic influenza vaccine during pregnancy: a prospective cohort study

Infection with influenza virus during pregnancy poses a significant risk of complications for both mother and fetus. During the H1N1 2009 pandemic, pregnant women constituted one of the priority groups for vaccination in many countries, creating a need for close monitoring of the safety of the vaccine in pregnant women. We present findings from an analysis of a cohort of pregnant women (N = 267) from a prospective, observational, post-authorization safety study of the AS03-adjuvanted split virion H1N1 (2009) pandemic vaccine. There were 265 known pregnancy outcomes with 261 live births, four spontaneous abortions with no congenital anomalies, and no stillbirths. There were six live births with congenital anomalies, of which one was diagnosed before vaccination. A total of 247 women (94.6%), of whom four had twin pregnancies, delivered at term, and 14 women (5.4%), of whom two had twin pregnancies, delivered preterm (between Weeks 24 and 36 of gestation), with three of them (1.1%) occurring before 32 weeks (very preterm). Twenty-one neonates (8.1%) had a low birth weight (<2.5 kg), of whom nine (3.5%) were term neonates. The prevalence of all outcomes was in line with the expected rates. The adverse events reported were consistent with the events anticipated to be reported by this study population. No adverse events of special interest were reported.The results of this analysis suggest that exposure to the AS03 adjuvanted H1N1 (2009) vaccine during pregnancy does not increase the risk of adverse pregnancy outcomes including spontaneous abortion, congenital anomalies, preterm delivery, low birth weight neonates, or maternal complications. Although limited in size, the fully prospective nature of the safety follow-up of these women vaccinated during pregnancy is unique and offers an important degree of reassurance for the use of the AS03 adjuvanted H1N1 (2009) vaccine in this high risk group for H1N1 infection.     

Child-bearing after induced abortion: reassessment of risk.

We reviewed 1791 singleton pregnancies of women with a history of previous induced abortion and compared them with 14,857 pregnancies in mothers with no previous induced abortions. Therapeutic termination of pregnancy was associated with a statistically significant increase in the incidence of low birth weight infants and bleeding in the first trimester of pregnancy. When other variables were examined, no significant differences were found between the two groups, except for a significantly higher rate of stillbirths among women who had not had a prior induced abortion. There were no increases in major or minor congenital malformations.     

Risks of delivery during the 20th to the 36th week of gestation

Using routinely collected maternity discharge data from 250,000 women in Scotland, we examined the risks of late spontaneous abortion and preterm delivery during the period 20 up to 36 weeks of gestation. Gestational age is treated as a fetal survival time and the risks of delivery associated with a history of spontaneous abortion, induced abortion and perinatal death are examined in a survival model controlling for several demographic and socioeconomic variables. The main objective of the study is to identify factors which are associated with high relative hazard of delivery early in the period, but with decreasing relative hazard of delivery as pregnancy progresses. The factor most clearly associated with converging hazards is a history of two or more spontaneous abortions, and this may reflect the tendency to repeat pregnancy outcome.     

高海拔地区藏族育龄妇女自然流产的流行病学特点

目的 了解中国高海拔地区15～49岁藏族育龄妇女自然流产状况。方法 采用横断面调查设计和分层多阶段抽样法获得样本，采用问卷调查西藏地区15～49岁藏族育龄妇女的生育史。结果 共调查3741名15～49岁的藏族育龄妇女，共计10245次妊娠，报告的自然流产386次，自然流产发生率为3墙％，城市妇女显著高于农村妇女，农牧区之间差异无统计学意义，育龄妇女发生自然流产的风险在控制了可能的影响因素后随着海拔高度的增加而增高。居住在海拔4500m以上的育龄妇女发生自然流产的风险是居住在海拔3500m以下妇女的近2倍多。年龄和妊娠的次数显著与自然流产的发生有正相关关系，35岁以上的育龄妇女和多次妊娠的妇女发生自然流产的风险增大。结论 高海拔可能独立的影响藏族妇女自然流产的发生，在高海拔地区更应加强健康教育和育龄妇女孕产期保健与营养，减少妊娠次数，延长生育间隔，以减少自然流产的发生。此外，回顾性的生育史调查可能会因回忆偏性等因素而低估了自然流产的发生，但西藏地区育龄妇女的自然流产水平不一定比平原地区高很多。