Maternal and Fetal Hemodynamics of Chronic Pregnant Smokers: A Doppler Study

Research Article

Austin Gynecol Case Rep. 2016; 1(1): 1005.

Maternal and Fetal Hemodynamics of Chronic Pregnant Smokers: A Doppler Study

Machado APLJ¹, Santos MC², Hattori WT², Paes MMBM³ and Diniz ALD¹*

¹Department of Obstetrics and Gynecology, Federal University of Uberlândia, Brazil

²Department of Public Health, Federal University of Uberlândia, Brazil

³Sector of Ultrasound, Federal University of Uberlândia, Brazil

*Corresponding author: Angélica L Debs Diniz, Departament of Obstetrics and Gynecology, Federal University of Uberlândia, Av. Para 1720-38405-320, Uberlândia-MG, Brazil

Received: June 08, 2016; Accepted: July 27, 2016; Published: July 29, 2016


Objectives: To evaluate the influence of chronic smoking on maternal-fetal hemodynamics through Doppler study of maternal uterine (UtA), fetal umbilical (UmA) and fetal middle cerebral (MCA) arteries compared to pregnant nonsmokers. The effect of the degree of nicotine addiction on this hemodynamics was also analyzed.

Methods: Observational cross-sectional study conducted in 98 chronic pregnant smokers and 102 pregnant non-smokers. Doppler study was performed for measuring Pulsatility Index (PI) and Resistance Index (RI) of UtA, UmA and MCA. Fargeström and exhaled Carbon Monoxide (COex) tests were analysed.

A multivariate general linear model with re sampling was applied. The significance level of 95% and 95% confidence intervals were adopted.

Results: Comparison of Doppler indexes between the two groups showed that only UtA RI and UmA PI had significant effect (p<0.001 and p=0.032, respectively), with higher values in pregnant smokers than non-smokers, indicating vasoconstriction and increase impedance in the studied vessels. Smoking had a positive effect for PI (p=0.045) and RI (p=0.007) of MCA, with significantly decreased indexes in smokers with high and very high dependence compared to low and moderate dependence. COex analysis showed elevated Um PI in moderate vs light smokers (p=0.035) whereas MCA RI was higher in light vs heavy smokers (p=0.024).

Conclusions: Chronic smoking interfered negatively on maternal-fetal vascular hemodynamics, as demonstrated by increased impedance in the maternal uterine and fetal umbilical arteries. Moreover, the greatest exposure to tobacco caused vasodilation effect in the fetal MCA, demonstrating that higher nicotine dependence, the greater the maternal-fetal hemodynamic changes.

Keywords: Doppler; Pregnancy; Smoking; Ultrasonography


Smoking remains a public health problem worldwide [1,2]. The cigarette has 4,000 active substances, including nicotine, tar, nitrosamines, polyaromatic hydrocarbons, formaldehyde hydrogen, cyanide and carbon monoxide [3]. Recent data indicate that one-third of US pregnant women and a quarter of Brazilian pregnant women are smokers [4]. Besides causing perinatal risks, maternal smoking can also affect the postnatal mental, intellectual and behavioral development of children exposed to smoking in fetal life [5].

In pregnancy, smoking is responsible for 20% of fetuses with low birth weight, 8% of premature births and 5% of all perinatal deaths [3]. Mothers who smoked during pregnancy had higher (66%) perinatal complications compared to non-smokers [6]. Although the greatest benefits for the fetal development occur if smoking cessation is still done in early pregnancy [5], stopping at any point in pregnancy, or even in the postnatal, has a significant impact on family health.

The effects of maternal smoking on the placental blood flow and vascular resistance are still controversial [7,8] but it is believed that their consequences on the fetal growth are probably mediated, at least in part, by a decrease of blood flow in the vascular beds of the placenta [9]. The mechanisms of action and damage caused by the cigarette consumption during pregnancy are complex, since it is the result of inhalation of a number of vasoactive substances, which have a range of effects that can be complementary or antagonistic at various levels within the vascular tree [10].

Several studies in the literature have used the Doppler method for analyzing the flow patterns in the maternal and fetal arteries of pregnant smokers with some divergent results [7,8,10-13]. The present study becomes relevant by analyzing the pulsatility and resistance indexes of the uterine, fetal umbilical and fetal middle cerebral arteries in chronic pregnant smokers who had the degree of nicotine dependence evaluated by specific tests.

The objective of this study was to evaluate the influence of chronic smoking on maternal and fetal hemodynamics by using Doppler study of the uterine, fetal umbilical and fetal middle cerebral arteries compared to a group of pregnant non-smokers. Furthermore, it was examined whether the degree of nicotine dependence causes effect in this hemodynamic profile. Our hypothesis is that there is a main effect of smoking on maternal and fetal hemodynamics. Moreover, when only pregnant mothers are considered, we hypothesized that there will be main effects of the Fagerström and Coex tests, but no interaction effect of these measures in the evaluation of the maternal and fetal hemodynamics.


Study design

This is an observational and analytical cross-sectional study conducted at the Clinic Hospital, Federal University of Uberlândia (UFU), Uberlândia, MG, Brazil. A total of 200 pregnant women, 98 smokers and 102 non-smokers, were subjected to analysis of six Doppler parameters between October 2011 and October 2013. This study was approved by the Research Ethics Committee of the Institution (number 420/10) and all patients who agreed to participate of the study signed an informed consent.

Patients were consecutively included in the study among those sent from the low risk prenatal in the Prenatal Clinic of UFU and municipal health units to perform obstetric ultrasonography. The inclusion criteria of study group were pregnant women with tobacco use for more than two years, with no known disease and using no medicines. The following criteria were met for inclusion in the study: single pregnancy, Gestational Age (GA) of 20 to 40 weeks, as defined by the embryonic and fetal cephalocaudal length in the 1st trimester of pregnancy, normal fetal anatomy during obstetric ultrasound examinations performed up to inclusion in the study; absence of placental abnormalities, such as placenta previa, circumvallate placenta with suspected acretism or any type of tumor; absence of changes in the umbilical cord, such as changed number of vessels, nodes, tumors or velamentous insertion into the placenta; absence of maternal diseases or conditions associated with changes in the fetal development, such as preeclampsia, diabetes or use of illegal drugs. The exclusion criteria was pregnant women who delivery in another Hospital or that stopped the prenatal at the Institution cited above. Five patients were excluded from the study.

To compare the variables between the groups, exposed and not exposed to tobacco, patients were divided into 5 subgroups according to the GA: 20 to 23 weeks + 6 days; 24 to 27 weeks + 6 days; 28 to 31 weeks + 6 days; 32 to 35 weeks + 6 days and>36 weeks.

Doppler ultrasound

All ultrasound examinations were performed by two experienced operators who used the Sonace 8000 equipment with convex transducer 2-6 MHz (Medison, South Korea). The fetal anatomy, the amount of amniotic fluid, and the characteristics and position of the placenta were evaluated in ultrasonography. In addition, the basic fetal biometry (biparietal diameter, head circumference, abdominal circumference and femur length) and the Doppler Velocimetry of the Uterine (UtA), Umbilical (UmA) and fetal Middle Cerebral (MCA) Arteries.

The evaluation was carried out with electronic convex Doppler transducer (3-5 MHz), 2-Hz PRF, 100-Hz filter and sample volume of 1.5 to 3 mm, depending on the analyzed vessel, with an angle less than 20 degrees. At least five waves of uniform flow velocities were obtained for the calculation of Resistance Index (RI) and Pulsatility Index (PI), which were made automatically by the instrument. The patients remained in semi-Fowler position during the examination.

Evaluations of the UmA and MCA were performed during fetal complete rest (including absence of breathing movements). The Doppler velocimetryof the UmA was made in manually. In the evaluation of the MCA, the sample volume was positioned in the proximal third of the vessel. For Doppler velocimetry of the UmA, the Doppler window was positioned up to two cm above the crossing of this vase with internal iliac arteries. The average of the RI and PI values obtained in both umbilical arteries were used for analysis [14].

Maternal and perinatal variables evaluated in this study were the maternal age at study entry and parity. The two groups were matched for gestational age. The birth weight of 75 newborns of smoking mothers was analyzed as well as the median gestational age at which the birth occurred.

Evaluation of the degree of nicotine dependence

Each patient programmed for ultrasound examination was submitted to the Fagerströmtest for Nicotine Dependence (FTND), which can be accepted as a useful measure of chronic ingestion of nicotine [15]. The FTND was presented by Fagerström, Heatherton and Kozlowski [16] and shows credibility in reports as a lowcost approach to obtain accurate information about the smoking behavior between men and women [17]. This instrument consists of a questionnaire with six questions with scores 0-2 and 0-3, and the degree of nicotine dependence evaluated on an increasing scale with the following values: 0-2, too low; 3-4, low; 5, moderate; 6-7, high; and 8-10, very high dependence. The FTND was translated and validated for the use in Brazil [18]. For teaching purposes, the patients were divided into two major subgroups: one with women with very low, low and moderate degree of dependence, and another with women presenting high and very high degree of dependence.

At this point, one sample of exhaled Carbon Monoxide (COex) was also collected using a portable breath carbon monoxide monitor (piCO+Smokerlyzer®, Bedfont Scientific Ltd, England).The exhaled CO is the most widely used biomarker for the diagnosis of smoking due to its reliability, simplicity and low cost [19]. The patients were instructed to take a deep breath, hold your breath for 20 sec and then exhale slowly through a nozzle. The estimated values of COex are as follows: up to 10 ppm, light smoker; 11-15 ppm, moderate smoker; over 16 ppm, heavy smoker.

Statistical analysis

The minimum sample size was calculated using the G* Power software [20,21], including the following parameters: effect size, f = 0.20; significance level, α = 0.05; test power, β = 0.95; six dependent variables; 10 subgroups. The 10 subgroups were composed of two categorical variables, that is, a combination of experimental conditions (control and experimental groups) and gestational ages, as described above. The calculation showed that the minimum sample size for this study would be 100 participants, which were divided by the 10 subgroups to identify the minimum sample size of each gestational age in each experimental condition. This procedure was adopted to prevent a confounding variable for gestational age.

A multivariate General Linear Model (GLM) with re sampling was applied to generate two different models. The first model was constructed to assess the main effect of experimental conditions. The second model, considering only the experimental group (smokers), tested the main effect of the categories of the Fagerström and Coex tests, in addition to the effect of interaction between these measures. In both models, the dependent variables were PI and RI of the UtA, UmA and MCA. For all analyzes, the significance level of 5%, bootstrap re sampling of 1000 samples and 95% confidence intervals were adopted.


Among the 98 pregnant smokers the birth weight of newborns could be assessed in 75 cases, with an average birth weight of 2931 ± 546 g and median birth age of 39 weeks, ranging between 32 and 41 weeks, with most births in fetuses to term. Table 1 shows the pairing of the number of pregnant women, study and control groups in different intervals of gestational age.