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; where 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 focused on cigarette as the mode of tobacco smoking. 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 unique health effects, which could not be fully captured by studies on cigarette smoking (17). In our large population-based cohort study, we found that 5.5% of the subjects were always smokers and 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 of the infant. We found that 42% of water pipe smokers (8% of all study subjects) quit water pipe smoking following pregnancy occurrence. Our study also showed that the mean birth weight of infants of quitters and always smokers was 99 and 137 grams lower than mean birth weight of infants of never smokers, respectively. The observed results were 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 a few studies (10, 18). The results of these investigations; however, relied heavily on the selected theoretical mechanism. In other words, early cessation of tobacco smoking would result in diluted 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. Consistently, Vilalbi et.al reported lower birth weight among infants of 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 population‐based prospective cohort study in the Netherlands (the Generation R Study) showed 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 compared to smoking continuation (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 smokers. 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. More specifically, our data showed that only 35 percent of the study subjects received regular prenatal checkups from healthcare centers, defined as nine routine checkups throughout pregnancy. In other words, more than two-thirds of pregnant women in our sample received 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 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. Such awareness programs should be well-targeted to pregnant women from the lowest socio-economic households. To elaborate more, our previous work showed that women with lower socio-economic status had lower knowledge regarding health effects of water pipe and higher unfavorable attitude towards water pipe smoking (3). In case of cigarette smoking, it is shown that to achieve the same risk of growth restriction 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 among 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 guaranteed suitable external generalizability to a wider population of pregnant women in the south of Iran. Large sample size (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.
In the absence of a ubiquitous valid tool, we used a self-report checklist to measure water pipe smoking during pregnancy. Therefore, observed differences in the estimated prevalence of water pipe smokers in our study with other estimates may be due to measurement biases, mainly reporting bias, stemmed from use of different self-report tools. Moreover, pregnant women who had medically assisted conception were excluded from the BAPC project. Hence, the estimated effects of water pipe on birth anthropometries should be interpreted with caution for this subgroup of women.