Chronic hypertension in pregnancy

Environmental Exposures and Congenital Heart Disease

Congenital heart disease (CHD) is the most common congenital abnormality worldwide, affecting 8 to 12 infants per 1000 births globally and causing >40% of prenatal deaths. However, its causes remain mainly unknown, with only up to 15% of CHD cases having a determined genetic cause. Exploring the complex relationship between genetics and environmental exposures is key in understanding the multifactorial nature of the development of CHD. Multiple population-level association studies have been conducted on maternal environmental exposures and their association with CHD, including evaluating the effect of maternal disease, medication exposure, environmental pollution, and tobacco and alcohol use on the incidence of CHD. However, these studies have been done in a siloed manner, with few examining the interplay between multiple environmental exposures. Here, we broadly and qualitatively review the current literature on maternal and paternal prenatal exposures and their association with CHD. We propose using the framework of the emerging field of the exposome, the environmental complement to the genome, to review all internal and external prenatal environmental exposures and identify potentiating or alleviating synergy between exposures. Finally, we propose mechanistic pathways through which susceptibility to development of CHD may be induced via the totality of prenatal environmental exposures, including the interplay between placental and cardiac development and the internal vasculature and placental morphology in early stages of pregnancy.

Prevalence and associated factors of birth defects among newborns in sub-Saharan African countries: a systematic review and meta-analysis

Introduction

Birth defects are the most serious causes of infant mortality and disability in sub-Saharan African countries with variable magnitude. Hence, this study was aimed to determine the pooled prevalence of birth defects and its associated risk factors among newborn infants in sub-Saharan African countries.

Methods

A total of 43 eligible studies were identified through literature search from Medline (PubMed), EMBASE, HINARI, Google scholar, Science Direct, Cochrane Library and other sources. Extracted data were analyzed using STATA 15.0 statistical software. A random effect meta-analysis model was used.

Results

Twenty-five studies in 9 countries showed that the pooled prevalence of birth defects was 20.40 per 1,000 births (95% CI: 17.04, 23.77). In the sub-group analysis, the highest prevalence was observed in southern Africa region with a prevalence of 43 per 1000 (95% CI: 14.89, 71.10). The most prevalent types of birth defects were musculo-skeletal system defects with a pooled prevalence of 3.90 per 1000 (95% CI: 3.11, 4.70) while the least was Down syndrome 0.62 per 1000 (95% CI: 0.40, 0.84). Lack of folic acid supplementation (95% CI: 1.95, 7.88), presence of chronic disease (95% CI: 2.00, 6.07) and intake of drugs (95% CI: 3.88, 14.66) during pregnancy were significantly associated with the birth defects.

Conclusion

The prevalence of birth defects is relatively high with high degree of regional variabilities. The most common types of birth defects were musculoskeletal defects. Lack of folic acid supplementation, presence of chronic disease and intake of drugs during pregnancy were significantly associated with birth defects.

Severe hypertension, preeclampsia and small for gestational age in women with chronic hypertension diagnosed before and during pregnancy

OBJECTIVES

To compare rates of severe hypertension (SH), preeclampsia (PE) birth of small for gestational age (SGA) neonates between women with chronic hypertension (CH) diagnosed during the first trimester of pregnancy and those with pre-pregnancy CH.

STUDY DESIGN

Prospective cohort study of women with CH and singleton pregnancies referred to an Antenatal Hypertension Clinic at 8-14 weeks' gestation. At presentation the patients were subdivided into four groups based on blood pressure (BP) control. Group 1 included women without a preceding history of CH presenting with BP of ≥140/90 mmHg (n = 86). Groups 2-4 had pre-pregnancy CH; in group 2 the BP was <140/90 mmHg without antihypertensive medication (n = 200), in group 3 the BP was <140/90 mmHg with antihypertensive medication (n = 231) and in group 4 the BP was ≥140/90 mmHg despite antihypertensive medication (n = 173).

MAIN OUTCOME MEASURES

PE, SH (BP ≥ 160/110 mmHg), SGA (birthweight < 10th percentile).

RESULTS

In group 1, the rate of SH (15.1%), was similar to that in group 2 (10.5%) and group 3 (23.8%) but significantly lower than in group 4 (52.6%). In group 1, the rate of PE (12.8%) and SGA <10th centile (18.6%) were similar to those in group 2 (16.5% and 21.0%) and significantly lower than in group 3 (26.0 and 30.7%) and group 4 (26.6% and 31.8).

CONCLUSION

In women diagnosed with CH in the first trimester of pregnancy, the rates of SH, PE and SGA are similar to those with pre-pregnancy CH who present with BP below 140/90 without the need for antihypertensive medication.

Chronic hypertension: first-trimester blood pressure control and likelihood of severe hypertension, preeclampsia, and small for gestational age

BACKGROUND

There is extensive evidence that prepregnancy chronic hypertension is associated with a high risk of development of severe hypertension and preeclampsia and birth of small-for-gestational-age neonates. However, previous studies have not reported whether antihypertensive use, blood pressure control, or normalization of blood pressure during early pregnancy influences the rates of these pregnancy complications.

OBJECTIVE

The purpose of this study was to stratify women with prepregnancy chronic hypertension according to the use of antihypertensive medications and level of blood pressure control at the first hospital visit during the first trimester of pregnancy and to examine the rates of severe hypertension, preeclampsia, and birth of small-for-gestational-age neonates according to such stratification.

STUDY DESIGN

We conducted a prospective study of 586 women with prepregnancy chronic hypertension, in the absence of renal or liver disease, that was booked at a dedicated clinic for the management of hypertension in pregnancy. The patients had singleton pregnancies and were subdivided according to findings in their first visit: group 1 (n=199), blood pressure <140/90 mm Hg without antihypertensive medication; group 2 (n=220), blood pressure <140/90 mm Hg with antihypertensive medication; and group 3 (n=167), systolic blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm Hg, despite antihypertensive medication. In the subsequent management of these pregnancies, our policy was to maintain the blood pressure at 130-140/80-90 mm Hg with the use of antihypertensive medication; antihypertensive drugs were stopped if the blood pressure was persistently <130/80 mm Hg. The outcome measures were severe hypertension (systolic blood pressure ≥160 mm Hg and/or diastolic blood pressure ≥110 mm Hg), preterm and term preeclampsia (in addition to hypertension at least 1 of renal involvement, liver impairment, neurologic complications, or thrombocytopenia), and birth of small-for-gestational-age neonates (birthweight <5th percentile for gestational age). The incidence of these complications was compared in the 3 strata.

RESULTS

The median gestational age at presentation was 10.0 weeks (interquartile range, 9.1-11.0 weeks). In groups 2 and 3, compared with group 1, there was a significantly higher body mass index, incidence of black racial origin, and history of preeclampsia in a previous pregnancy. There was a significant increase from group 1 to group 3 in the incidence of severe hypertension (10.6%, 22.2%, and 52.1%), preterm preeclampsia with onset at <37 weeks of gestation (7.0%, 15.9%, and 20.4%), and small for gestational age (13.1%, 17.7%, and 21.1%), but not term preeclampsia with onset at ≥37 weeks of gestation (9.5%, 9.1%, and 6.6%).

CONCLUSIONS

In women with prepregnancy chronic hypertension, the rates of development of severe hypertension, preterm preeclampsia, and small for gestational age are related to the use of antihypertensive medications and the level of blood pressure control at the first hospital visit during the first trimester of pregnancy.

Risk of Miscarriage in Women Receiving Antidepressants in Early Pregnancy, Correcting for Induced Abortions

BACKGROUND

Earlier studies on the association between antidepressant use and miscarriage have obtained conflicting results after accounting for the role of depression, and none have taken into account the high risk of induced abortions in women using antidepressants.

METHODS

We identified 41,964 pregnant women delivering between 1998 and 2002 using Quebec's health administration databases. We compared women prescribed antidepressants in the first trimester and with a recorded diagnosis of depression before pregnancy to (1) women with neither antidepressant use nor a depression diagnosis before or during pregnancy; (2) women with a depression diagnosis before pregnancy, but no antidepressants prescribed in the first trimester; and (3) women prescribed hypothyroid medication in the first trimester, but not antidepressants. We used log binomial regression to assess the adjusted relative risk of miscarriage, corrected for induced abortion risk.

RESULTS

The miscarriage risk uncorrected for induced abortions was 16%, 10%, and 9% for depressed women exposed to antidepressants; unexposed depressed women; and unexposed, nondepressed women, respectively. These decreased to 11%, 8%, and 7% after correction for induced abortions. In multivariable analysis, the corrected risk of miscarriage relative to unexposed, nondepressed women was 1.3 (1.1-1.5) for antidepressant-exposed women and 1.1 (1.0-1.2) for unexposed depressed women. The miscarriage relative risk for antidepressant users compared with unexposed depressed women was thus 1.2 (1.0-1.4).

CONCLUSIONS

Antidepressant use in the first trimester is associated with an increased risk of miscarriage when compared with either nondepressed or depressed unexposed women, even after accounting for induced abortions.

Obstetric and offspring risks of women's morbid conditions linked to prior anticancer treatments

BACKGROUND

Literature shows the effects of type of cancer and/or anticancer treatment on live birth percentages and/or pregnancy and neonatal complications in female cancer survivors. However, studies analyzing the obstetric and offspring risks of the morbid conditions associated with previous anti-cancer treatments are missing. The present review aims to uncover these risks.

METHODS

A literature search based on publications up to March 2016 identified by PubMed and references cited in relevant articles.

RESULTS

The morbid conditions associated with prior anticancer treatments including chemotherapy, radiotherapy, surgery, and/or hematopoietic stem-cell transplant may induce not only obstetric and neonatal complications but also long-term effects on offspring. Whereas some risks are predominantly evidenced in untreated women others are observed in both treated and untreated women. These risks may be superimposed on those induced by the current women's trend in Western societies to postpone maternity.

CONCLUSIONS

Medical professionals should be aware and inform female cancer survivors wishing to have a child not only of the short- and long-term risks to themselves and their prospective offspring of previous anticancer treatments, fertility-preservation technologies, and pregnancy itself, but also of those risks linked to the morbid conditions induced by prior anticancer treatments. Once female cancer survivors wishing to have a child have been properly informed about the risks of reproduction, they will be best placed to make decisions of whether or not to have a biological or donor-conceived child. In addition, when medical professionals be aware of these risks, they will be also best placed to provide appropriate treatments before/during pregnancy in order to prevent or alleviate the impact of these morbid conditions on maternal and offspring health.

Maternal Hypertension During Pregnancy and the Risk of Congenital Heart Defects in Offspring: A Systematic Review and Meta-analysis

Maternal hypertension is common during pregnancy, and multiple studies have reported on an association between maternal hypertension and congenital heart defects (CHDs) in offspring; however, there is variability in the quality of these studies. A systematic review and meta-analysis was conducted on the associations between untreated and treated maternal hypertension and the risk of CHDs, evaluating CHDs overall as well as specific CHD subtypes. A systematic search of peer-reviewed articles published before August 2013 identified 16 studies evaluating the associations between untreated and treated maternal hypertension and CHDs. Summary relative risk (RR) estimates were calculated using fixed-effects models and random-effects models. Significant associations were observed between maternal hypertension and overall CHDs, for both treated [RR 2.0; 95 % confidence interval (CI) 1.5, 2.7] and untreated (RR 1.4; 95 % CI 1.2, 1.7) hypertension, as well as for overall hypertension regardless of treatment status (RR 1.8; 95 % CI 1.5, 2.2). The magnitude of effect was similar for the majority of CHD subtypes evaluated. The effects were also similar among women with hypertension who used one of multiple specific hypertension medications. There was no evidence of publication bias, and our results were robust to several factors considered in sensitivity analyses (e.g., source of exposure data, adjustment for potential confounders, and study design). Maternal hypertension was associated with CHDs. By understanding the specific mechanisms involved, appropriate strategies may be developed to reduce this risk, in order to prevent CHDs.

Involvement of T lymphocytes in the placentae with villitis of unknown etiology from pregnancies complicated with preeclampsia

OBJECTIVE

The aim of the study was to compare immunohistochemical expression of different T type lymphocytes in foci of villitis of placentae with villitis of unknown etiology (VUE) without and with preeclampsia (PE).

METHODS

Fifty-four placentae were collected from women who had VUE with (N = 27) and without (N = 27) PE. Immunohistochemistry for types of T lymphocytes was performed on formalin fixed and paraffin-embedded sections by use of the CD3, CD4, FOXP3, CD25, CD8 and CD68 antibodies. All data analyses were done by R Development Core Team.

RESULTS

There was higher immunohistochemical CD4 positive T lymphocyte count and CD4 positive/CD8 positive ratio in placentae with VUE complicated with PE compared to control group.

CONCLUSION

The higher immunohistochemical CD4 positive T lymphocyte count and CD4 positive/CD8 positive ratio in placentae with VUE complicated with PE could point to their role in ethiopathogenesis of PE.

Factors associated with major structural birth defects among newborns delivered at Muhimbili National Hospital and Municipal Hospitals in Dar Es Salaam, Tanzania 2011 - 2012

Introduction

Ninety-four percent of all birth defects and 95% of deaths due to the birth defects occur in low and middle income countries, Tanzania among them. In Tanzania there are currently limited birth defects prevention strategies in place due to limited information on factors associated with the occurrence of birth defects.

Methods

We conducted a case control study that included newborns born from October, 2011 through February, 2012 at 4 participating hospitals. A case was defined as any newborn of a Dar es salaam resident with a neural tube defect, orofacial clefts, limb reduction defects or musculo-skeletal defects (SBD) born during the study period. A control was defined as the next three newborns (delivered after the case) without birth defects. Univariate, bivariate and multivariate analysis were done using Epi Info version 3.5.1.

Results

A total of 400 newborns participated in the study, 100 cases and 300 controls. Factors associated with higher odds of a SBD included maternal fever (adjusted odds ratio (AOR) = 1.99; 95% confidence interval (CI): 1.14-3.52), maternal hypertension (AOR = 3.99; 95% CI: 1.67-9.54), and low birth weight (AOR = 3.48; 95% CI: 1.77-6.85). Antimalarial use during pregnancy was protective (AOR = 0.48; 95% CI: 0.28-0.84). Folic acid supplementation was protective only in bivariate analysis (OR = 0.56; 95% CI: 0.32-0.96).

Conclusion

Maternal fever, hypertension, and low birth weight are associated with higher odds of SBD. Antimalarial use during pregnancy was associated with lower odds of SBD. Early screening of pregnant mothers for hypertension and other causes of low birth weight may reduce SBD in Dar Es Salaam.

Maternal hypertension with nifedipine treatment associated with a higher risk for right-sided obstructive defects of the heart: a population-based case-control study

OBJECTIVE

To establish possible aetiological factors contributing to congenital heart defects (CHD) overall and separately for different types of CHD, as causes are unknown for the vast majority of patients.

DESIGN

To estimate a possible association with maternal diseases and related drug treatments as exposures in the mothers of cases with right-sided obstructive defects of the heart (RSODH).

SETTING

A large population-based Hungarian Case-Control Surveillance of Congenital Abnormalities data set.

PATIENTS

Newborn infants with four types of RSODH based on autopsy or surgical records.

INTERVENTIONS

Comparison of 200 live-born cases with RSODH including 72 (36.0%) with pulmonary valve stenosis, 13 (6.5%) with tricuspid atresia/stenosis, 7 (3.5%) with Ebstein's anomaly and 108 (54.0%) with pulmonary atresia, with 304 matched controls and 38 151 population controls without any defects.

MAIN OUTCOME MEASURES

Risk of any RSODH and risk of each type of RSODH.

RESULTS

High blood pressure, particularly chronic hypertension with nifedipine treatment, was associated with a risk for RSODH (OR 7.03, 95% CI 3.13 to 13.84). High doses of folic acid reduced the birth prevalence of pulmonary atresia (OR 0.29, 95% CI 0.16 to 0.53).

CONCLUSIONS

The multifactorial threshold model provides the best explanation for the origins of RSODH. Genetic predisposition may be triggered by maternal hypertension with nifedipine treatment, while the risk for pulmonary atresia is reduced by high doses of folic acid in early pregnancy.

Maternal medical and behavioral risk factors for congenital diaphragmatic hernia

PURPOSE

Maternal factors contributing to the etiology of congenital diaphragmatic hernia (CDH) remain unclear. We hypothesized that specific maternal medical conditions (pregestational diabetes, hypertension), and behaviors (alcohol, tobacco) would be associated with CDH.

METHODS

We conducted a population-based case-control study using Washington State birth certificates linked to hospital discharge records (1987-2009). We identified all infants with CDH (n=492). Controls were randomly selected among non-CDH infants. Maternal data were extracted from the birth record. Logistic regression was used to adjust for covariates.

RESULTS

Cases and controls were generally similar regarding demographics, although CDH infants were more likely to be male than controls (58.5% vs. 52.5%). Isolated and complex (multiple-anomaly) CDH had similar characteristics. Each of the exposures of interest was more common among case mothers than among control mothers. In univariate analysis, alcohol use, hypertension, and pregestational diabetes were each significantly associated with the outcome. After multivariate adjustment, only alcohol use (OR=3.65, p=0.01) and pregestational diabetes (OR=12.53, p=0.003) maintained significance. Results were similar for both isolated and complex CDH.

CONCLUSIONS

Maternal pregestational diabetes and alcohol use are significantly associated with occurrence of CDH in infants. These are important modifiable risk factors to consider with regard to efforts seeking to impact the incidence of CDH.

Management of chronic hypertension during pregnancy with furosemide, amlodipine or aspirin: a pilot clinical trial

OBJECTIVE

To determine the maternal and neonatal efficacy and safety with furosemide, amlodipine or aspirin in women with mild/moderate chronic hypertension during pregnancy.

METHODS

A pilot clinical trial was performed in a tertiary teaching hospital in Panama. Pregnant patients with mild/moderate chronic hypertension at ≤20 weeks of gestation were invited to take part in the study. Mild/moderate chronic hypertension was defined as a pregnancy with systolic blood pressure of 140-159 mmHg or diastolic blood pressure of 90-109 mmHg. Women in the furosemide group received 20 mg of furosemide oral each day, those in the amlodipine group received 5 mg of amlodipine oral each day and those in the aspirin group received 75 mg of orally-administered acetylsalicylic acid each day.

RESULTS

We enrolled 63 patients during the study period, 21 women were randomised to each group (aspirin, amlodipine and furosemide). We found no difference in maternal complications, pre-term births, mean birth weight or in the proportion of small for gestational age infants among treatment groups. Severe hypertension and aggregate pre-eclampsia were similar among treatment groups.

CONCLUSION

This pilot trial demonstrates that both furosemide and amlodipine might have the same effect during pregnancy. However, a large clinical trial is necessary to prove this.

Nongenetic risk factors and congenital heart defects

Advances have been made in identifying genetic etiologies of congenital heart defects. Through this knowledge, preventive strategies have been designed and instituted, and prospective parents are counseled regarding their risk of having an affected child. Great strides have been made in genetic variant identification, and genetic susceptibility to environmental exposures has been hypothesized as an etiology for congenital heart defects. Unfortunately, similar advances in understanding have not been made regarding strategies to prevent nongenetic risk factors. Less information is available regarding the potential adverse effect of modifiable risk factors on the fetal heart. This review summarizes the available literature on these modifiable exposures that may alter the risk for congenital heart disease. Information regarding paternal characteristics and conditions, maternal therapeutic drug exposures, parental nontherapeutic drug exposures, and parental environmental exposures are presented. Factors are presented in terms of risk for congenital heart defects as a group. These factors also are broken down by specific defect type. Although additional investigations are needed in this area, many of the discussed risk factors present an opportunity for prevention of potential disease.

Quality of obstetric care in the sparsely populated sub-arctic area of Norway 2009-2011

Background

It is challenging to obtain high quality obstetric care in a sparsely populated area. In the subarctic region of Norway, significant distances, weather conditions and seasonable darkness have called for a decentralized care model. We aimed to explore the quality of this care.

Methods

A retrospective study employing data (2009–11) from the Medical Birth Registry of Norway was initiated. Northern Norwegian and Norwegian figures were compared. Midwife administered maternity units, departments at local and regional specialist hospitals were compared. National registry data on post-caesarean wound infection (2009–2010) was added. Quality of care was measured as rate of multiple pregnancies, caesarean section, post-caesarean wound infection, Apgar score <7, birth weight <2.5 kilos, perineal rupture, stillbirth, eclampsia, pregnancy induced diabetes and vacuum or forceps assisted delivery. There were 15,586 births in 15 delivery units.

Results

Multiple pregnancies were less common in northern Norway (1.3 vs. 1.7%) (P = 0.02). Less use of vacuum (6.6% vs. 8.3%) (P = 0.01) and forceps (0.9% vs 1.7%) (P < 0.01) assisted delivery was observed. There was no difference with regard to pregnancy induced diabetes, caesarean section, stillbirth, Apgar score < 7 and eclampsia. A significant difference in birth weight < 2.5 kilos (4.7% vs. 5.0%) (P < 0.04) and perineal rupture grade 3 and 4 (1.5% vs. 2.3%) (P < 0.02) were revealed. The post-caesarean wound infection rate was higher (10.5% vs. 7.4%) (P < 0.01).

Conclusion

Northern Norway had an obstetric care of good quality. Birth weight, multiple pregnancies and post-caesarean wound infection rates should be further elucidated.

Hypertension and antihypertensive drugs in pregnancy and perinatal outcomes

OBJECTIVE

Despite high rates of hypertension in pregnancy, the effects of hypertension have not been separated appropriately from the effects of the medications that are used. We evaluated the safety of exposure to antihypertensive medications during pregnancy, while accounting for disease effects.

STUDY DESIGN

A population-based retrospective cohort study was performed that compared all pregnancies of women with hypertension who were either exposed or unexposed to antihypertensive medications. A computerized database of the medications that were dispensed to pregnant women from 1998-2008 was linked with computerized databases that contained maternal and infant hospitalization records from the district hospital during the same period.

RESULTS

During the study period, 100,029 deliveries occurred; of those, 1964 pregnant women experienced chronic hypertension, and 620 neonates (0.6%) were exposed to at least 1 antihypertensive medication (methyldopa or atenolol) during pregnancy. A higher rate of intrauterine growth restriction (7.2% vs 2.1%, respectively; adjusted odds ratio [OR], 4.37; 95% confidence interval [CI], 3.00-6.36; P < .001), small for gestational age (3% vs 1.7%, respectively; adjusted OR, 2.23; 95% CI, 1.27-3.92; P = .005), and preterm deliveries (<37 weeks, 22.9% vs 8.0%, respectively; adjusted OR, 3.69; 95% CI, 2.90-4.69; P < .001) were noted among the pregnancies of women who were exposed to antihypertensive medications during the third trimester. Importantly, a similar association was detected when we compared women with chronic hypertension who were not treated during pregnancy (n = 1074) to women who had no chronic hypertension and who were unexposed to antihypertensive medications (n = 97,820).

CONCLUSION

Chronic hypertension with or without treatment during pregnancy is an independent and significant risk factor for adverse perinatal outcomes such as intrauterine growth restriction, small for gestational age, and preterm delivery.

Relationship between maternal asthma, its severity and control and abortion

STUDY QUESTION

Are women with asthma, and more specifically those with severe or uncontrolled asthma, at higher risk of spontaneous and induced abortions?

SUMMARY ANSWER

Pregnant women with asthma, notably when uncontrolled, are at higher risk of spontaneous abortion.

WHAT IS KNOWN ALREADY

Only one study has examined the association between asthma and spontaneous and induced abortions and revealed a modest increase in the risk of spontaneous abortions, particularly in women with more severe asthma and those with previous exacerbations, and a marginal decrease in the risk of induced abortions.

STUDY DESIGN, SIZE, DURATION

A cohort of pregnancies from asthmatic (n = 15,107) and non-asthmatic (n = 34,331) women was reconstructed by linking three administrative databases from Quebec (Canada), between 1992 and 2002. The cohort included 7870 spontaneous abortions, 14,596 induced abortions and 26,972 live births.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Pregnant women with and without asthma were analyzed. Asthma was defined by at least one asthma diagnosis and one dispensed prescription for an asthma medication in the 2 years prior to or during pregnancy. Asthma severity and control were assessed using validated indexes in the year before the 20th week of pregnancy or the termination of the pregnancy. Logistic polytomous regression models were used to estimate the relationship between asthma and asthma severity and control on the risk of abortion, while adjusting for potential confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

The prevalence of spontaneous and induced abortions was 15.9 and 29.5%, respectively. Maternal asthma was associated with an increased risk of a spontaneous abortion [odds ratio (OR) = 1.41; 95% confidence interval (CI): 1.33-1.49] and a decreased risk of induced abortions (OR = 0.92; 0.88-0.97). No association was observed between asthma severity and abortion, while uncontrolled asthma increased the risk of a spontaneous abortion by 26% (95% CI: 14-41%) and the risk of induced abortions by 11% (95% CI: 1-21%).

LIMITATIONS, REASONS FOR CAUTION

It is possible that the study results were confounded by imbalances between groups in variables that are not recorded in the databases, but that are known to be associated with spontaneous abortions, such as alcohol consumption, obesity or maternal smoking. However, we performed sensitivity analyses which revealed that these factors are unlikely to explain the observed increased risk for a spontaneous abortion. It is also possible that women with asthma are more likely to have abortions recorded in the databases, because subjects with a chronic disease tend to visit a physician more often than those without asthma. Therefore, our odds estimates for these outcomes may be overestimated when asthmatic women were compared with non-asthmatic women. A further limitation of the study is that it would have been more appropriate to measure the severity and control of asthma only during the pregnancy.

WIDER IMPLICATIONS OF THE FINDINGS

Our cohort is less representative of women in the upper socio-economic level. This is not a threat to internal validity, but it could limit the external validity if the impact of asthma on the risk of abortion differed according to the socio-economic status of the mother. Despite the absence of supporting data, this possibility cannot be completely excluded.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Canadian Institutes of Health Research and Genentech. L.B. received research grants from Astra-Zeneca, Pfizer, sanofi-aventis, Novartis and Merck for research projects and co-chairs the Astra-Zeneca Endowment Pharmaceutical Chair in Respiratory Health. F.Z.K and A.F. have no competing interests to declare.