Placenta mediates the association between maternal second-hand smoke exposure during pregnancy and small for gestational age

doi:10.1016/j.placenta.2015.05.005

Placenta

Volume 36, Issue 8, August 2015, Pages 876-880

https://doi.org/10.1016/j.placenta.2015.05.005 Get rights and content

Highlights

•
Perinatal second-hand smoke (SHS) was significantly associated with placental weight and small for gestational age (SGA).
•
Placental weight decline was significantly associated with SGA.
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Placental weight mediated the association of perinatal SHS exposure with SGA.

Abstract

Introduction

The causal relationship between maternal second-hand smoke (SHS) exposure during pregnancy and small for gestational-age (SGA) has been affirmed, but the mechanism is still unclear. Previous studies have found that the placenta remarkably affects fetal intrauterine growth and that SHS exposure during pregnancy impairs placental growth and decreases placental weight. Therefore, the placenta may mediate the association between maternal SHS exposure during pregnancy and SGA. This study explores whether and to what extent the association between maternal SHS exposure during pregnancy and SGA is mediated by the placenta.

Methods

We investigated 562 pregnant women delivering SGA newborns (cases) and 1581 delivering appropriate-for-gestational-age newborns (controls) in this case–control study. Information on maternal SHS exposure during pregnancy, socio-demographic characteristics and obstetric conditions, including placental weight, were collected at the Maternity and Child Health Care Hospitals of Shenzhen and Foshan in Guangdong, China. Linear and hierarchical logistic regression models were fitted to examine the mediation effects of placental weight on the association between maternal SHS exposure during pregnancy and SGA.

Results

After controlling for ethnicity, maternal age, educational level, family income, pre-pregnancy body mass index (BMI), parity, gestational age and newborn gender, maternal SHS exposure during pregnancy was associated with a higher SGA risk (adjusted odds ratio (OR) = 1.26; 95% confidence interval (CI) = 1.03–1.55) and lower placental weight (standard deviation (SD) = −0.15, SE = 0.04). Regression models illustrated that placental weight partially mediated (49.6%; 95% CI = 35.9–63.3%) the association between SHS exposure during pregnancy and SGA.

Discussion

Our findings suggest that the placenta plays an intermediary role in how maternal prenatal SHS exposure affects fetal growth.

Introduction

Small-for-gestational-age (SGA) newborns, whose birth weight is lower than the 10th percentile of their normal counterparts of the same sex and gestational age, are commonly considered to be a result of restricted intrauterine growth [1]. The prevalence of SGA is 9.7% globally [2] and 6.4% in southern China [3]. Accumulated evidence has suggested that SGA not only elevates the risk of perinatal morbidity and mortality but also increases the risk of behavioural problems in adolescents [4] and metabolic diseases in adulthood [5]. Researchers have therefore focused on the risk factors for SGA and its potential mechanisms.

Previous studies have indicated that SGA is a result of a complex combination of maternal, placental and fetal factors. Maternal exposure to second-hand smoke (SHS) during pregnancy is a common and preventable maternal risk factor for SGA [6], [7]. A recent meta-analysis revealed that maternal exposure to SHS during pregnancy led to a 33–40-g decrease in birth weight and a 1.22–1.32-fold increase in low-birth-weight (LBW) risk [8]. Although the association between maternal SHS exposure during pregnancy and SGA has been well documented, its mechanism is still controversial and inconclusive.

The placenta is a vital organ responsible for transporting nutrients and oxygen from the mother to the fetus and discharging waste from the fetus to the mother. It plays an important role in perinatal outcomes [9], [10]. For instance, previous studies have indicated that placental weight is correlated with birth weight and fetal intrauterine growth [11], [12], [13], [14], [15]. Maternal smoking during pregnancy has been found to impair placental structure and function [16]. Ouyang et al. [17] suggested that placental weight partially mediated the association of maternal pre-pregnancy body mass index (BMI), weight gain and gestational diabetes with fetal growth. Few studies have reported whether the placenta also mediates the association between maternal SHS exposure during pregnancy and SGA. This study explores whether and to what extent the association between maternal SHS exposure during pregnancy and SGA is mediated by the placenta.

Section snippets

Study design and participants

A case–control study was conducted from September 2009 to March 2011 at the Foshan and Shenzhen Women and Children's Hospitals in Guangdong, southern China, Fig. 1 shows the flow chart of our study participants. The inclusion criteria were as follows: (a) self-reported non-smoking; (b) a singleton birth; (c) a newborn without malformation; (c) no pre-existing chronic renal disease, lung disease, diabetes, hypertension, hyperthyroidism or anaemia; (d) no history of induced or accidental

Socio-demographic and obstetric characteristics of the participants

Table 1 compares the socio-demographic and obstetric characteristics of the SGA cases and AGA controls. The placental weight in SGA (448.5 g) was restricted in comparison with the placental weight in AGA (497.1 g). Mothers who gave birth to SGA newborns were more frequently exposed to SHS during pregnancy (45.0% vs. 38.4%). Other than gestational age and newborn gender, the socio-demographic and obstetric characteristics of the SGA cases and AGA controls were similar.

Association of placental weight with maternal SHS exposure during pregnancy

After controlling for the

Discussion

In this case–control study, we found that placental weight was significantly associated with both maternal SHS exposure during pregnancy and SGA. Maternal SHS exposure during pregnancy significantly increased the risk of SGA. Placental weight mediated the association between maternal SHS exposure during pregnancy and SGA, with an effect of 49.6%. These findings suggest that the placenta may play a mediating role in how SHS exposure during pregnancy causes SGA.

There is abundant evidence that

Conflicts of interest

The authors have no conflicts of interest to declare.

Acknowledgement

This study was supported by the National Natural Science Foundation of China (Grant Numbers 30872164 & 81172758). The authors acknowledge the support of the Shenzhen Women and Children's Hospital and Foshan Women and Children's Hospital.

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Placenta mediates the association between maternal second-hand smoke exposure during pregnancy and small for gestational age

Highlights

Abstract

Introduction

Methods

Results

Discussion

Introduction

Section snippets

Study design and participants

Socio-demographic and obstetric characteristics of the participants

Association of placental weight with maternal SHS exposure during pregnancy

Discussion

Conflicts of interest

Acknowledgement

Eur J Obstet Gynecol Reprod Biol

Placenta

Eur J Obstet Gynecol Reprod Biol

Placenta

Pathol Res Pract

Early Hum Dev

Cytokine

Placenta

Placenta

Placenta

Application of a global reference for fetal-weight and birthweight percentiles in predicting infant mortality

BJOG – Int J Obstet Gynecol

A new birthweight reference in Guangzhou, southern China, and its comparison with the global reference

Arch Dis Child

Fetal growth and childhood behavioral problems: results from the ALSPAC cohort

Am J Epidemiol

Fetal and placental size and risk of hypertension in adult life

BMJ

Patterns of tobacco exposure before and during pregnancy

Acta Obstet Gynecol Scand

The economic burden of smoking and secondhand smoke exposure in rural South-West China

J Asthma: Off J Assoc Care Asthma

Environmental tobacco smoke and fetal health: systematic review and meta-analysis

Arch Dis Child Fetal Neonatal Ed