- Smoking during pregnancy | March of Dimes
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- 10 Risks of Smoking During Pregnancy
Several factors can lead to premature birth, for example, underlying infection or some anatomical considerations. Besides, smoking during pregnancy is also an important factor that may cause preterm birth. Since nicotine exposure leads to several complications of pregnancy and birth, the risk for preterm birth is higher among women who smoke during pregnancy. There are several elements contributing to the alteration of steroid hormone production and changes of the responses to oxytocin such as hypoxia resulting from carbon monoxide and vasoconstriction resulting from nicotine [ 6 ].
Unlike other unavoidable factors for preterm birth, tobacco smoking is an environmental exposure which can be easily eliminated, and even short behavioral interventions can be effective. Transport of the fertilized egg through the fallopian tube is controlled by ciliary beating and smooth muscle contractility [ 8 ]. Ectopic pregnancy tubal pregnancy , or eccyesis, is a complication of pregnancy in which the embryo attached outside the uterus [ 9 ].
Ectopic pregnancy in the fallopian tubes are more common among smoking women as nicotine or other substances of cigarettes may lead to the turnover of altered epithelial cell in the fallopian tube and result in the dysfunction of fallopian tube. Several risk factors of damaging or killing cilia can result from smoking, thus increasing the time for the embryo to reach the uterus.
The embryo, which cannot reach the uterus in time, will implant itself inside the fallopian tube, causing the ectopic pregnancy [ 10 ].
Besides ectopic pregnancy, cigarette smoking during pregnancy also leads to other human reproduction disorders such as spontaneous abortion and infertility [ 11 ]. PROM, also known as rupture of membranes occurring in pregnancy, refers to breakage of the amniotic sac.
Smoking during pregnancy | March of Dimes
There is amniotic fluid surrounding and protecting the fetus in the uterus contained in the sac including two membranes, the chorion and the amnion. When rupture occurs, the fluid leaks out of the uterus through the vagina. Fetal membranes will be likely to be broken because they become weak and fragile. This change is usually a normal process that happens along with the body preparing for labor or delivery. However, this will become a problem when premature birth occurs. Cigarette smoking during pregnancy leads to the abnormal weakness of fetal membranes by the factors of cell death and poor assembly of collagen, and even breakdown of collagen [ 13 ].
Similar with overweight, smoking during pregnancy is shown as an inverse risk factor for hypertensive disorders of pregnancy such as pregnancy-induced hypertension and preeclampsia. Studies demonstrate that, compared with women of normal weight, pregnancy-induced hypertension and gestational hypertension are more common among overweight women, especially in overweight women who smoke.
The risk for hypertensive disorders increases 2—3 times among overweight and obese women [ 14 , 15 ], which reflects an independent effects of obesity or smoking habits on the hypertensive disorders. On the contrary, there is an inverse association that smoking in women of normal weight has potential effect of decreasing the risk of pregnancy-induced hypertensive disorders.
However, there is no clinical proof of the potentially positive effect of nicotine exposure on hypertensive disorders. It is hypothesized that the combustion of tobacco products circulating angiogenic proteins, which could be released through carbon monoxide [ 6 , 17 ].
Several studies have demonstrated that fetuses with prenatal nicotine exposure have lower birth weight than their peers [ 18 , 19 ], and the findings are consistent with intrauterine growth restriction [ 20 , 21 ]. Imaging examination shows that this growth restriction affects brain, kidney, lung, and other lean and fatty tissues. Overall fetal volume and placental volume are also decreased, which may result in embryo damage and miscarriages, thus increasing the infant mortality [ 22 , 23 ]. This effect is found to be dose-dependent.
There is a decreased birth weight by an average of 2. The mechanism of fetal growth restriction is under debate. Several initial studies demonstrated that fetal hypoxia is induced by the carbon monoxide or other combustion products [ 6 , 25 ]. However, it is observed that using electronic cigarettes also results in fetal growth restriction, making this view seems less likely [ 22 ].
Numerous researchers agree that smoking during pregnancy significantly increases the resistance of placental blood flow, which is associated with fetal growth restriction [ 26 , 27 ]. It may be seen that fetal growth restriction results from nicotine, which leads to the vasoconstriction. While there is another theory proposing that decreased supply of amino acids contributes to fetal growth restriction.
Nicotine exposure blocks the cholinergic receptor and impairs amino acid transport [ 28 ], while the hypoxia resulting from carbon monoxide also limits the transport of amino acids. SIDS is one of the main reasons for death among healthy infants [ 29 ]. It is defined as the sudden death of 1-year-old neonates. SIDS seems to occur when a neonate has an underlying biological vulnerability, such as premature infants or low-birth-weight infants, or has problems in the part of the brain [ 31 ].
Studies show that SIDS rates are higher in infants with fetal growth restriction resulting from prenatal nicotine exposure [ 32 ]. The study of Zhang and Wang [ 33 ] also suggested that maternal smoking could increase the risk of SIDS, and it was dose-dependent. Mitchell and Milerad [ 34 ] discovered that the exposure of the fetus to tobacco is associated with SIDS. They also suggested that if maternal smoking is avoided, about one-third of SIDS deaths might have been hold back. Similar to fetal restriction, studies proved that prenatal smoking could affect growth patterns over the long term, with height deficits documented in childhood through to adulthood [ 35 ].
A recent study has proposed that despite birthing with lower weights, children of mothers who smoke during pregnancy tend to be overweight [ 37 , 38 ], and such an effect will last for a lifetime [ 39 , 40 ]. It is noted that alterations in ghrelin concentrations are likely to be involved [ 41 ].
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Thus, the offspring of smoking mothers takes more risk of suffering from type 2 diabetes [ 42 , 43 ]. Alternatively, endocrine imbalances could occur at critical developmental periods. Studies point out negative effects of prenatal smoking on reproductive system. The menarche may be earlier in females exposed to nicotine prenatally [ 25 ].
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In males, analysis of semen samples points out that prenatal nicotine exposure results in poor semen quality and decreased sperm count [ 44 , 45 ]. This indicates that such long-term health consequences are not confined to one generation, but also continued to impair the health of a future generation. Maternal smoking can also influence fetal lung development and lung function.
The embryonic immune function will have over reaction to certain substances, thus producing antibodies, which are easy to cause allergic diseases after the baby was born. Pulmonary function testing demonstrates that the impaired lung function of children is associated with the exposure to nicotine prenatally [ 46 , 47 ]. Compared with their peers, the incidents of respiratory tract infections and compromised lung function e. These changes will impair the gas-exchange ability of the pulmonary parenchyma, leading to a directly increased amount of work for respiration [ 50 ].
As is shown that nicotine increases placental vascular resistance [ 52 , 53 ], children with maternal nicotine exposures tend to have a greater risk of hypertension throughout the whole life [ 54 , 55 ]. Further studies show that women who smoke during pregnancy put their fetus at a higher risk of birth defects, especially congenital heart defects than their peers [ 56 , 57 ]. They chose newborns with congenital heart septal defects and randomly selected newborns without any defects. They found that smoking during pregnancy can increase the risk of congenital heart septal defects in infants.
However, the effect of smoking during pregnancy on the progeny of hypertension is not clear. Since there are many toxic chemicals in tobacco, smoking during pregnancy can restrict the head growth, change the structure and function of the brain, and have lifelong bad effects on the fetal brains. In addition to the direct impact of the chemical composition, evidence suggests that smokers are more susceptible to depression and refuse to take health promoting actions. To be specific, smokers will not receive prenatal care timely and recognize their pregnancies later [ 60 ]. Along with the adverse effects of nicotine on the fetal brain, children of smokers are more likely to have learning disorders or behavioral problems.
They found that maternal cigarette smoking can lead to smaller brain volumes, smaller cortical gray and white matter volumes of children, and these children will also have thinner superior frontal, superior parietal, lateral occipital, and precentral cortices, and show more behavioral and emotional problems. In conclusion, smoking during pregnancy can cause bad effects on the growth of the fetal head and influence the normal brain function [ 61 ]. However, the mechanisms of how these bad effects happen on the fetus need more research.
We all know that maternal active smoking is harmful to pregnant women and the fetus; however, more and more studies have showed that passive smoking is also a hidden threat [ 62 ]. In recent years, many anti-smoking activities have been carried out in public places to prevent nonsmoking women and children who suffer from passive smoking.
However, bad effects of passive smoking on pregnant women have not been widely publicized because they are less clear, and many people are still not aware of them.
10 Risks of Smoking During Pregnancy
So more studies should be carried out to ensure bad outcomes of pregnant women associated with passive smoking. Several studies have demonstrated that smoking during pregnancy takes effects through epigenetic mechanisms, just like other environmental factors. They deemed that maternal cigarette smoking was associated with incorrect DNA methylation patterns, which were important for the health of the embryo, and it could also lead to the aberrant expression of miRNA.
Therefore, many biological processes would be disturbed. Rent with DeepDyve.
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