Smoking and orofacial clefts: a United Kingdom-based case-control study

Secondhand smoke and adverse fetal outcomes in nonsmoking pregnant women: a meta-analysis

OBJECTIVE

To determine the risk of adverse fetal outcomes of secondhand smoke exposure in nonsmoking pregnant women.

METHODS

This was a systematic review and meta-analysis in accordance with Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines. We searched Medline and Embase (to March 2009) and reference lists for eligible studies; no language restrictions were imposed. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated by using random-effect models. Our search was for epidemiologic studies of maternal exposure to secondhand smoke during pregnancy in nonsmoking pregnant women. The main outcome measures were spontaneous abortion, perinatal and neonatal death, stillbirth, and congenital malformations.

RESULTS

We identified 19 studies that assessed the effects of secondhand smoke exposure in nonsmoking pregnant women. We found no evidence of a statistically significant effect of secondhand smoke exposure on the risk of spontaneous abortion (OR: 1.17 [95% CI: 0.88-1.54]; 6 studies). However, secondhand smoke exposure significantly increased the risk of stillbirth (OR: 1.23 [95% CI: 1.09-1.38]; 4 studies) and congenital malformation (OR: 1.13 [95% CI: 1.01-1.26]; 7 studies), although none of the associations with specific congenital abnormalities were individually significant. Secondhand smoke exposure had no significant effect on perinatal or neonatal death.

CONCLUSIONS

Pregnant women who are exposed to secondhand smoke are estimated to be 23% more likely to experience stillbirth and 13% more likely give birth to a child with a congenital malformation. Because the timing and mechanism of this effect is not clear, it is important to prevent secondhand smoke exposure in women before and during pregnancy.

Maternal cigarette smoking and the associated risk of having a child with orofacial clefts in China: a case-control study

BACKGROUND

We investigated whether maternal and paternal cigarette smoking during early pregnancy could increase the risk of delivering an infant with an orofacial cleft.

METHODS

A case-control study was carried out in China. 304 infants born with an isolated nonsyndromic oral cleft and 453 non-malformed controls were recruited as participants and their exposure to smoke plus family history data were collected.

RESULTS

The relative odds ratios of maternal smoking to cause an orofacial cleft in infant increased for 3.30 (95% CI, 1.17-9.33) in CLO and 3.12 (95% CI, 1.24-7.84) in CLP from 1 to 10 cigarettes per day before pregnancy. The unadjusted odds ratio is 3.64 (95% CI, 1.01-13.19) and the adjusted OR is 7.00 (95% CI, 1.44-34.13) in CLO from 1 to 10 cigarettes during the first trimester. Paternal smoking in the periconceptional period was strongly associated with all subtypes of CLP. The association with medium ETS (2-6h) at home or at work was strongest for infants with all OFCs in the periconceptional period from 1 month before pregnancy through the end of the first trimester.

CONCLUSION

This study confirmed the modest association between maternal smoking and orofacial clefts.

Environmental tobacco smoke exposure and perinatal outcomes: a systematic review and meta-analyses

BACKGROUND

While active maternal tobacco smoking has well established adverse perinatal outcomes, the effects of passive maternal smoking, also called environmental tobacco exposure (ETS), are less well studied and less consistent.

OBJECTIVE

To determine to the effect of ETS on perinatal outcomes.

SEARCH STRATEGY

Medline, EMBASE and reference lists were searched.

SELECTION CRITERIA

Studies comparing ETS-exposed pregnant women with those unexposed which adequately addressed active maternal smoking.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed titles, abstracts, full studies, extracted data and assessed quality. Dichotomous data were pooled using odds ratios (OR) and continuous data with weighted mean differences (WMD) using a random effects model.

MAIN RESULTS

Seventy-six articles were included with a total of 48,439 ETS-exposed women and 90,918 unexposed women. ETS-exposed infants weighed less [WMD -60 g, 95% confidence interval (CI) -80 to -39 g], with a trend towards increased low birthweight (LBW, < 2,500 g; RR 1.16; 95% CI 0.99-1.36), although the duration of gestation and preterm delivery were similar (WMD 0.02 weeks, 95% CI -0.09 to 0.12 weeks and RR 1.07; 95% CI 0.93-1.22). ETS-exposed infants had longer infant lengths (1.75 cm; 95% CI 1.37-2.12 cm), increased risks of congenital anomalies (OR 1.17; 95% CI 1.03-1.34) and a trend towards smaller head circumferences (-0.11 cm; 95% CI -0.22 to 0.01 cm).

CONCLUSIONS

ETS-exposed women have increased risks of infants with lower birthweight, congenital anomalies, longer lengths, and trends towards smaller head circumferences and LBW.

Human cleft lip and palate fibroblasts and normal nicotine-treated fibroblasts show altered in vitro expressions of genes related to molecular signaling pathways and extracellular matrix metabolism

Nonsyndromic cleft lip with or without cleft palate (CLP) is a frequent craniofacial malformation caused by both genetic and environmental factors. Maternal smoking during pregnancy is a known risk factor, due to the teratogenic role of nicotine. To assess and compare the impact of CLP and nicotine, we studied the quantitative expression of genes involved in signaling pathways and extracellular matrix (ECM) metabolism in human normal nicotine-treated (NicN) and CLP fibroblasts compared to normal control (CTRL) cells. Palatal fibroblast cultures from seven CLP children and seven age-matched CTRL subjects were established and subconfluent cells incubated for 24 h without (CTRL and CLP fibroblasts) or with (NicN fibroblasts) 0.6 mM nicotine. Gene expressions were analyzed by real-time quantitative PCR. For the first time, a regulated cholinergic signaling in our human fibroblasts in vitro was demonstrated. Members of TGF-beta, retinoic acid (RA), and GABA-ergic signaling systems were also differently regulated. Among the ECM genes, fibronectin, syndecan, integrin alpha2, and MMP13 genes were concordantly modulated, while integrin beta5, and decorin genes were discordantly modulated. Interestingly, nicotine treatment regulated gene expressions of CD44 and CLPTM1, two candidate genes for CLP. Our findings show a positive association between nicotine treatment and CLP phenotype. Results suggest that nicotine deranges normal palate development, which might contribute to the development of a CLP malformative phenotype, through the impairment of some important signaling systems and ECM composition.

Cleft lip and palate

Clefts of the lip and palate are generally divided into two groups, isolated cleft palate and cleft lip with or without cleft palate, representing a heterogeneous group of disorders affecting the lips and oral cavity. These defects arise in about 1.7 per 1000 liveborn babies, with ethnic and geographic variation. Effects on speech, hearing, appearance, and psychology can lead to longlasting adverse outcomes for health and social integration. Typically, children with these disorders need multidisciplinary care from birth to adulthood and have higher morbidity and mortality throughout life than do unaffected individuals. This Seminar describes embryological developmental processes, epidemiology, known environmental and genetic risk factors, and their interaction. Although access to care has increased in recent years, especially in developing countries, quality of care still varies substantially. Prevention is the ultimate objective for clefts of the lip and palate, and a prerequisite of this aim is to elucidate causes of the disorders. Technological advances and international collaborations have yielded some successes.

Analysis of interactions between genetic variants of BMP4 and environmental factors with nonsyndromic cleft lip with or without cleft palate susceptibility

A hospital-based case-control study was conducted to identify interactions between the 538(T-->C) polymorphic site of bone morphogenetic protein 4 gene (BMP4T538C) and exposures in pregnancy with nonsyndromic cleft lip, with or without cleft palate (nsCL/P). Associations between offspring polymorphism of BMP4T538C, paternal smoking, paternal high-risk drinking, maternal passive smoking, and maternal multivitamin supplement with nsCL/P were analyzed by logistic regression analysis. BMP4T538C polymorphism, maternal passive smoking exposures and maternal multivitamin use were associated with the risk of nsCL/P but paternal smoking and paternal high-risk drinking were not. Gene-environment interactions were analyzed using the multifactor dimensionality reduction (MDR) method. The two-factor model including maternal passive smoking and BMP4T538C, was the best for predicting nsCL/P risk with a maximum cross-validation consistency (10/10) and a maximum average testing accuracy(0.605; P<0.0001). The findings suggested that: BMP4T538C could be used as a genetic susceptibility marker for nsCL/P; maternal passive smoking exposure is a risk factor for nsCL/P; maternal multivitamin supplements are a protective factor; the synergistic effect of BMP4T538C and maternal passive smoking could provide a new tool for identifying individuals at high risk of nsCL/P, and provides additional evidence that nsCL/P is determined by genetic and environmental factors.

From the American Academy of Pediatrics: Technical report--Secondhand and prenatal tobacco smoke exposure

Secondhand tobacco smoke (SHS) exposure of children and their families causes significant morbidity and mortality. In their personal and professional roles, pediatricians have many opportunities to advocate for elimination of SHS exposure of children, to counsel tobacco users to quit, and to counsel children never to start. This report discusses the harms of tobacco use and SHS exposure, the extent and costs of tobacco use and SHS exposure, and the evidence that supports counseling and other clinical interventions in the cycle of tobacco use. Recommendations for future research, policy, and clinical practice change are discussed. To improve understanding and provide support for these activities, the harms of SHS exposure are discussed, effective ways to eliminate or reduce SHS exposure are presented, and policies that support a smoke-free environment are outlined.

Bayesian methods for correcting misclassification: an example from birth defects epidemiology

BACKGROUND

Cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO) are common congenital malformations. Numerous epidemiologic studies have shown an increased risk for orofacial clefts among children whose mothers smoked during early pregnancy; however, there is concern that the results of these studies may have been biased because of exposure misclassification. The purpose of this study is to use previous research on the reliability of self-reported cigarette smoking to produce corrected point estimates (and associated credible intervals) of the effect of maternal smoking on children's risk of clefts.

METHODS

We accounted for misclassification using 4 Bayesian models that made different assumptions about the sensitivity and specificity of self-reported maternal smoking data. We used results from previous studies to specify the prior distributions for sensitivity and specificity of reporting and used Markov chain Monte Carlo algorithms to calculate the posterior distribution of the effect of maternal smoking on children's risk for CL/P and CPO.

RESULTS

After correcting for potential sources of misclassification in data from the National Birth Defects Prevention Study, we found an increased risk of CL/P among children born to mothers who smoked during early pregnancy (posterior odds ratio [OR] = 1.6, 95% credible interval = 1.1-2.2). The posterior effect of smoking on CPO provided less evidence of effect (posterior OR = 1.1, 95% credible interval = 0.7-1.7).

CONCLUSION

Our results lend some credibility to the hypothesis that periconceptional maternal smoking increases the risk of a child being born with CL/P. The results concerning CPO provide no overall evidence of effect, although the estimates were relatively imprecise. We suggest that future research should emphasize validity studies, especially those of differential reporting, rather than replicating existing analyses of the relationship between maternal smoking and clefts. We discuss how our approach is also applicable to evaluating misclassification in a wide range of exposure-outcome scenarios.

Folate and Clefts of the Lip and Palate—A U.K.-Based Case-Control Study: Part I: Dietary and Supplemental Folate

Objectives:

We sought to determine the associations between nonsyndromic cleft lip with or without cleft palate (CL−P) and cleft palate only (CP) and maternal intake of dietary folate and supplemental folic acid, in an area where the prevalence at birth of neural tube defects has been high and flour is not fortified with folic acid.

Methods:

Interviews regarding periconceptional dietary intake and supplement use were completed with the mothers of 112 CL−P cases, 78 CP cases, and 248 unaffected infants. The data were analyzed by logistic regression methods.

Results:

There was no overall association between CL−P and CP and either energy-adjusted total folate intake or supplemental folic acid use, irrespective of dosage.

Conclusion:

Overall, higher intakes of total folate do not appear to prevent oral clefts in this population.

Maternal smoking and oral clefts: the role of detoxification pathway genes

BACKGROUND

There is evidence for an effect of cigarette smoking on risk of oral clefts. There are also hypothetical pathways for a biologic effect involving toxic chemicals in cigarette smoke.

METHODS

We performed a combined case-control and family-triad study of babies born with oral clefts in Norway in the period 1996 to 2001, with 88% participation among cases (n = 573) and 76% participation among controls (n = 763). Mothers completed a questionnaire 4 months after birth of the baby. DNA was collected from parents and children, and assayed for genes related to detoxification of compounds of cigarette smoke (NAT1, NAT2, CYP1A1, GSTP1, GSTT1, and GSTM1).

RESULTS

For isolated cleft lip (with or without cleft palate) there was a dose-response effect of smoking in the first trimester. The odds ratio rose from 1.6 (95% confidence interval = 1.0-2.5) for passive smoking to 1.9 (0.9-4.0) for mothers who smoked more than 10 cigarettes per day. There was little evidence of an association with cleft palate. Genetic analyses used both case-control and family-triad data. In case-triads we found an association between a NAT2 haplotype and isolated cleft lip (relative risk of 1.6 with 1 copy of the allele and 2.5 with 2 copies), but with little evidence of interaction with smoking. Other genes did not show associations, and previously described interactions with smoking were not confirmed.

CONCLUSION

First-trimester smoking was clearly associated with risk of cleft lip. This effect was not modified by variants of genes related to detoxification of compounds of cigarette smoke.

Air pollutant effects on fetal and early postnatal development

Numerical research on the health effects of air pollution has been published in the last decade. Epidemiological studies have shown that children's exposure to air pollutants during fetal development and early postnatal life is associated with many types of health problems including abnormal development (low birth weight [LBW], very low birth weight [VLBW], preterm birth [PTB], intrauterine growth restriction [IUGR], congenital defects, and intrauterine and infant mortality), decreased lung growth, increased rates of respiratory tract infections, childhood asthma, behavioral problems, and neurocognitive decrements. This review focuses on the health effects of major outdoor air pollutants including particulates, carbon monoxide (CO), sulfur and nitrogen oxides (SO(2), NOx), ozone, and one common indoor air pollutant, environmental tobacco smoke (ETS). Animal data is presented that demonstrate perinatal windows of susceptibility to sidestream smoke, a surrogate for ETS, resulting in altered airway sensitivity and cell type frequency. A study of neonatal monkeys exposed to sidestream smoke during the perinatal period and/or early postnatal period that resulted in an altered balance of Th1-/Th2-cytokine secretion, skewing the immune response toward the allergy-associated Th2 cytokine phenotype, is also discussed.

Prevention of orofacial clefts: does pregnancy planning have a role?

OBJECTIVE

To investigate the association between pregnancy planning and orofacial clefts in the United Kingdom.

DESIGN

Case-control study.

SETTING

Scotland and the Manchester and Merseyside regions of England.

PARTICIPANTS

One hundred and ninety-one children born with nonsyndromic orofacial cleft, 1997 to 2000, and 247 controls.

MAIN OUTCOME MEASURE

Cleft lip with and without cleft palate, and cleft palate.

RESULTS

There was an inverse association between planning for pregnancy and orofacial cleft in the offspring (odds ratio [OR] = 0.51, 95% confidence interval [CI] = 0.33-0.79). An unplanned pregnancy together with smoking in the first trimester of pregnancy resulted in almost treble the risk of a child with an orofacial cleft when compared with those who planned their pregnancy and did not smoke (OR = 2.92, CI = 1.50-5.65).

CONCLUSIONS

Planned pregnancies were associated with a lower risk of orofacial clefts. Isolation of the elements of pregnancy planning implicated in these results is difficult. Current preconception advice needs to reach a wider audience; however, for maximum impact, efforts are needed to reduce the numbers of unplanned pregnancies.

Maternal Smoking and Environmental Tobacco Smoke Exposure and the Risk of Orofacial Clefts

BACKGROUND

Smoking during pregnancy has been associated with orofacial clefts in numerous studies. However, most previous studies have not been able to assess the relation between maternal smoking and specific phenotypes (eg, bilateral clefts).

METHODS

We examined the association between periconceptional maternal smoking, environmental tobacco smoke (ETS) exposure, and cleft lip with or without cleft palate (CLP) (n = 933) and cleft palate only (CPO) (n = 528) compared with infants with no major birth defects (n = 3390). Infants were born between 1 October 1997 and 31 December 2001, and exposures were ascertained from maternal telephone interviews for the National Birth Defects Prevention Study. We excluded infants who had a first-degree relative with an orofacial cleft. Effect estimates were adjusted for folic acid use, study site, prepregnancy obesity, alcohol use, gravidity, and maternal age, education, and race/ethnicity.

RESULTS

Periconceptional smoking was associated with CLP (odds ratio = 1.3; 95% confidence interval = 1.0-1.6), and more strongly associated with bilateral CLP (1.7; 1.2-2.6), with a weaker association observed for CPO. Heavy maternal smoking (25+ cigarettes/day) was associated with CLP (1.8; 1.0-3.2), bilateral CLP (4.2; 1.7-10.3), and CPO with Pierre Robin sequence (2.5; 0.9-7.0). ETS exposure was not associated with CLP or CPO.

CONCLUSIONS

This study confirmed the modest association between smoking and orofacial clefts that has been consistently reported, and identified specific phenotypes most strongly affected.

Effect of N'-nitrosonornicotine (NNN) on murine palatal fusion in vitro

Maternal smoking has been linked to an increased risk for orofacial clefts. N'-nitrosonornicotine (NNN) is one of the tobacco-specific nitrosamines that has been shown to be linked to the deleterious effects of tobacco and could be linked to the formation of cleft palate birth defects. The effect of NNN on palatal fusion was examined using an in vitro organ culture model of palatal development. The organ cultures were exposed to NNN (0.01, 0.1, 1, 10 and 100 mM) and the effects on palatal development characterized at defined points. Palatal fusion was evaluated at embryonic day 13 (E13)+72 h by characterizing the remaining medial edge epithelium (MEE) and determining the extent of fusion compared to controls. The NNN-treated group (1 mM) had more MEE remaining in the palatal midline than the untreated group at E13+72 h (P<0.05). Changes in cell proliferation in the MEE resulting from NNN exposure were examined by BrdU incorporation in replicating DNA. Changes in the pattern of MEE cell death were examined by TUNEL. BrdU incorporation and TUNEL staining showed that the NNN (1 mM)-treated palates had more MEE cell proliferation and less apoptosis than the untreated-palates at E13+24 h (P<0.05). The mechanism altered by NNN was further evaluated by characterizations of extracellular signal-regulated kinase (ERK) 1/2, p38 and c-jun amino-terminal kinase (JNK). NNN at 1 mM induced ERK1/2 phosphorylation, but reduced p38 phosphorylation (P<0.05, P<0.01, respectively) in the MEE. The results suggest that NNN inhibited palatal fusion by effects on cell proliferation and MEE cell death.