Exposure to maternal tobacco smoking during pregnancy is a well-recognized cause of fetal growth restriction and preterm birth (14). Tobacco smoking during pregnancy can increase the risk of fetal growth restrictions up to two times, while nearly one-quarter of all infants with growth restriction can be attributed to tobacco smoking (15, 16). Regardless of the underlying theory for the effects of smoking cessation on infant health, all the previous studies have focused on cigarette as the mode of smoking. Nevertheless, our study attempted to provide a clearer picture on the effects of water pipe cessation on pregnancy outcomes. In spite of similar health consequences of various types of tobacco smoking, water pipe has been shown to have unique health effects, which could not be captured by studies on cigarette smoking (17). In our large population-based cohort study, we found that 5.5% of subjects were always smoker; while nearly 8% of the subjects quitted water pipe following pregnancy notification. Our study showed that continuation of water pipe smoking during pregnancy was associated with a substantial reduction in birth weight. We found that 42% of water pipe smokers (8% of all study subjects) quit water pipe smoking following pregnancy occurrence. Our study revealed that, the mean birth weight in infants of quitters and always smokers was 99 and 137 grams lighter than mean birth weight in infants of never smokers, respectively. The results we observed are biologically plausible. The effects of maternal tobacco smoking on fetal growth are complex and mainly grounded on two theoretical mechanisms. It may result from an interaction between genetic traits and direct toxic effects of nicotine, or may be due to the placental-smoking interaction. Positive effects of cessation of cigarette smoking on pregnancy outcomes have been reported in few studies (10, 18). The results of these investigations; however, have relied heavily on the selected theoretical mechanism. In other words, early cessation of tobacco smoking results in less effect in the former mechanism; whereas a critical window of exposure emerged in the first trimester in the latter one (18, 19). Setting aside different concepts, both aforementioned theories imply that the time of cessation might be an important predictor in the pathway of smoking cessation on pregnancy outcomes. Our findings supported the premise that smoking impedes growth and fetal weight gain and reinforced prior conclusions that quitting tobacco smoking will bring about major improvement in fetal growth and birth anthropometries. For instance, Vilalbi et.al reported lower birth weight among mothers who continued cigarette smoking during pregnancy in Spain. The authors concluded that the effects of smoking was most prominent for intra-uterine growth retardation (20).The results of a study on the data from the Generation R Study, a population‐based prospective cohort study in the Netherlands, has shown that although pre-conception active cigarette smoking was not associated with adverse pregnancy outcomes; continued active smoking in pregnancy increased the odds of low birthweight by 75%. The authors also reported that quitting smoking in early pregnancy was associated with a higher birthweight than continuing to smoke. (21).
Notwithstanding, the present study has provided a novel piece of information indicating that quitting water pipe smoking during pregnancy might substantially improve fetal growth in water pipe smoking mothers. The estimated effect of quitting water pipe on birth anthropometries remained even after adjusting on preterm birth and second-hand water-pipe smoking, implying the extent to which primary prevention on smoking cessation may be beneficial for all pregnant women. For instance, our data showed that regular prenatal checkups, defined as nine routine checkups throughout pregnancy from healthcare centers, were received by only 35% of all study subjects. In other words, more than two-thirds of pregnant women in our sample received their prenatal care from private physicians or did not receive it at all. Interestingly, the proportion of women not receiving prenatal care from any sources was significantly higher among always smokers; whereas, never smokers received the care more frequently from healthcare centers (data not shown). This observation has brought an important implication. Encouragement to initiate prenatal healthcare services as soon as possible may assist pregnant women in making the decision to quit water pipe in pregnancy. Such awareness programs should pay special attention to pregnant women from disadvantaged socio-economic households, since our previous work showed that lower socio-economic status was strongly related to less knowledge and attitude about the adverse effects of water pipe smoking (3). In case of cigarette smoking, it has been shown that to achieve the same risk of growth restrictions as non-smoking mothers, quitting must be adopted before conception (9, 10), although it is still efficient at earlier points during pregnancy (18). Having a similar logic for water pipe smoking, cessation programs should focus on benefits of quitting in preconception period or as early in pregnancy as possible.
Our study was amongst the first attempts to quantify birth anthropometric measures following various patterns of water pipe smoking during pregnancy. Our study used data from a population-based prospective cohort study, which has guaranteed a suitable external generalizability to a wider population of pregnant women in South of Iran. Large sample size of our study (n =1,120) provided satisfactory statistical power to strengthen the precision of our estimates. While previous studies mostly evaluated a single birth outcome such as birthweight, we studied all the three standard anthropometric measures, including weight, length, and head circumference. Nevertheless, our study has suffered from some limitations. In the absence of a ubiquitous valid tool to measure water pipe smoking during pregnancy, we used a self-report checklist to measure the exposure of interest. Therefore, variations in the estimated prevalence of water pipe smokers in our results with others are likely due to measurement biases, mainly reporting bias, stemmed from use of different self-report tools. Moreover, exclusion criteria of the BAPC project excluded pregnant women who had medically assisted conception. Hence, the observed effects of water pipe on birth anthropometries should be interpreted with caution for this subgroup of women.