Asma A. Al- Jawadi *†
Zina W. A. Al-Mola**†
Raghad A. Al- Jomard***†
*Professor of Public Health & Preventive Medicine. Department of Community Medicine, College of Medicine ,University of Mosul, Mosul, Iraq (Address of correspondence).
Email: asmaa_aljawadi@yahoo.com
** Community Medicine Specialists, Ninevah Directorate of Health , Mosul, Iraq.
Email: bannder@yahoo.com
***Assistant researcher, Environmental Health Education & Resources Unit, College of Medicine, Mosul, Iraq.
Email: Raghad0@yahoo.com
† Equal contribution

INTRODUCTION

As far as the exposure to environmental elements is concerned, attention has been directed to study the exposure to lead, and since its health effects may begin during exposure in uterus, the study of maternal exposure is of significance^[1].

The Center for Disease Control and Prevention (CDC) has grouped blood lead values into three ranges: (1) low (1 - 10 µg/ dl); (2) moderate (11 - 20 µg / dl); (3) high (20 - 38 µg/ dl)^[2]. Needleman and Landrigan in 2004 stated that, there is no demonstrated safe concentration of lead in blood, a large part of adverse health effects occur at the lowest doses^[3].

During pregnancy stores of lead deposited in bones over life may be mobilized and transferred to the more bioavialable compartment of the maternal circulation with potential toxic effects on the fetus and mother^[4]. This possibility of bone resorption during pregnancy is alarming in view of a study linking even lower levels of lead exposure may be associated with deficits in neurobehavioral function in infants. Early 3rd trimester of pregnancy may constitute a critical period for subsequent intellectual child development during which lead exposure can produce lasting and possibly permanent effects^[5]. Neurodevelopment involvement from prenatal and early childhood exposures have been observed at a relatively low level of lead and it may be the most sensitive end point for its toxicity^[6].

The period of fetal growth is often the stage of development at which an organism is most sensitive to toxic agents. However, fetal exposure cannot be directly measured during pregnancy in human research studies. Maternal measurements are the only exposure indices ethically available^[7].

The effects of lead on fetal growth, intrauterine development, and postnatal status have long been of concern in occupational and environmental medicine. Lead in a large amount has been shown to be fetotoxic in humans, prenatal lead exposure likely increases the risk of preterm delivery and inconsistently associated with reduced Apgar score at delivery, birth weight, head circumference, and recumbent length^[8].

Maternal BLLs (MBLLs) were also associated with increase of systolic and diastolic blood pressure as well as increased risk of 3rd trimester hypertension^[9].
The main concern of the present study is to monitor the association of MBLLs with pregnancy outcomes among the study sample.

Prior to data collection an official permission was obtained from Nineveh Health Office and Maternity Hospitals Administrations that were to be involved in this work. A written consent was taken from participants prior to the interview and blood sample collection.

The present study was conducted in Mosul city, the center of Nineveh Governorate. Data collection was carried out in the main maternity hospitals in Mosul; selected on the basis of having the largest number of monthly births, and their accessibility for the whole population living in this city.

In this study a cross-sectional design was adopted among women who attended the delivery units in the chosen hospitals. A sample of 370 maternal-fetal pairs was considered which forms almost 10% of the average monthly attendance distributed over the chosen hospitals. Out of this numbers 350 pairs were reached. The inclusion criteria for the study participants were:
(1) She is 15-49 years old.
(2) Mosul city resident for more than 3 years.
(3) Has a full term single viable pregnancy.
(4) Has no gestational diabetes or seizure.
(5) Has no psychiatric illness.
(6) Delivered by normal vaginal delivery.

Data were obtained directly from mothers who signed a letter of consent before collection of blood samples. Collected information included mother's age, parity, and blood pressure (BP) which was measured before delivery. A woman was considered hypertensive if one measurement of diastolic BP was 110 mmHg or more, or diastolic BP more than 90 mmHg on two occasions four hours apart.

Hemoglobin (Hb) level was obtained from the maternal case sheet. A woman was included among the anemic group if her Hb level was <11g/dl^[10].

Birth weight (BW) was measured immediately after birth. Neonates weighing less than 2.5 kg were regarded as a low birth weight (LBW) baby^[11]. Head circumference (HC) was measured using non-stretchable tape and recorded to the nearest cm. A normal baby should have a HC of 35 cm or more [12]. Apgar score more than 7 was regarded as normal^[12].

Blood lead levels analysis
Analysis of blood lead was performed at the Environmental Health Education and Recourses unit of Mosul College of Medicine.

Blood Lead Levels (BLLs) were estimated by using LEADCARE® Blood Lead Testing System and Lead Care Blood Lead Testing Kits by (ESA, Inc., USA). This system relied on electrochemistry and a unique sensor to detect lead in the whole blood. The contents of these kits are used specifically with LEADCARE® Analyzer and Blood Lead Testing System.

Three ml of venous maternal blood samples were collected in lead free EDTA tubes and the same volume of umbilical cord blood was also collected immediately after birth from each corresponding newborn baby in EDTA tubes as well.

Fresh whole blood samples were thoroughly mixed in their EDTA tubes and accurately measured. 50 µL samples were transferred and mixed with treatment reagent until they turned brown. An exactly measured 50 µL blood mixture was then transferred to the kidney shaped active area of the sensor using the 50 µL pipette that was supplied with the LEADCARE® System.

With the sensor properly placed into the sensor holder and its active area thoroughly covered with the mixture, it was then pushed the rest of the way into the sensor holder where the analyzer displayed the BLL in µg/dl, after exactly 180 seconds. The range of the test is 1.4 - 65 µg/dl. "Hi" in the display window indicates that BLLs are greater than 65 µg/dl.

Analyses of refrigerated blood mixtures in the treatment reagent tubes were made in weekly batches. Mixtures were allowed to reach room temperature prior to analysis.

LEADCARE® Blood Lead Controls were used to monitor the accuracy and precision of blood lead testing. They are prepared from bovine blood containing metabolized lead and they consist of a low level blood lead control; 6.4± 3.0 µg/dl (Level 1) and a high level blood lead control; 25.9± 4.0 µg/dl (Level 2).

Each control contains 2.0 ml lyophilized bovine whole blood that should be reconstituted with the provided 2.0 ml LEADCARE® water with isothizolones (< 0.002%) as preservative. Reconstituted controls were used as would be a patient blood sample and as an internal quality control program.

Statistical Methods
Data were analyzed with a SPSS package version 13. Blood lead concentrations were log transformed due to non-normal distributions. Unpaired T-test was used to determine the presence or absence of significant differences between the two means. Pearsons' correlation was performed to find the degree of correlation between MBLLs and umbilical BLLs (UBLLs).

Chi- squared (X2) test was used to test for the presence or absence of significant association between elevated MBLLs and pregnancy outcomes. Odds ratio (OR) and the corresponding 95% confidence interval (CI) were also computed. P-value of <0.05 was considered significant throughout the present study.

Overall , out of 370 maternal infants pairs were reached making a participation rate of 94.6%
Table 1 exhibits characteristics of maternal-infant pairs. The geometric mean (GM) of MBLLs at delivery was 3.26±1.91 µg/ dl with a range of 0.50-22.39 µg/ dl. The GM of lead concentration in the umbilical cord blood was 2.29±22.11 µg/ dl; the range was 0.30-22.29 µg/ dl. A highly significant difference was reported between the two GMs (p=0.000). On average, the UBLLs were lower than MBLLs by 0.97 µg/ dl. Using untransformed data: 57 pairs (16.3%) had an umbilical blood lead value higher than their mothers.

Figure 1 portrays a significant positive correlation between MBLLs and UBLLs (r= 0.856, p= 0.001).
Table 2 clarifies the effect of MBLLs on the development of hypertension and anemia among women participants during the current pregnancy. Women with BLLs =10 µg/ dl are more at risk of developing hypertension than those with BLLs= 10 µg/ dl (OR= 6.84, p= 0.000). Although there is an evident risk of anemia development among women with high BLLs (OR=2.73) this risk does not reach a significant level

Table 3 shows that mothers with high BLLs (=10 µg/ dl) are more at risk of having a low BW baby, (OR= 43.54, p= 0.000). Also such mothers have babies with fairly significant small HC (OR= 3.16, P= 0.013). However, no effect was significantly shown on the Apgar score of such newborns.

x² test was used

x² test was used

Figure 1: Correlation between MBLLs and UBLLs

The survey of targeted populations at a special risk for either lead exposure or toxic health effects can provide improved, cost - effective means for eventual control of exposure. Prenatal lead exposure is of concern because it may have an effect on cognitive development and may increase delinquent and antisocial behaviors when the child gets older and it may also reduce neonatal weight gain. In addition to fetal risk, lead may be a risk to mothers by causing an increase in blood pressure^[13].

There is an ongoing debate over the appropriate cut-off point of blood lead concentration of concern in infants and young children. Consequently, it was lowered by CDC from 60 µg / dl in 1960 to 25 µg / dl and then to the currently used value of 10 µg / dl in 1991. Two factors brought about this reduction: improved investigational strategies and reduced background lead levels due to removal of lead from gasoline^[14].

Mosul is a densely populated city. It is the second largest city in Iraq. Like other cities in this country, it is facing several environmental health problems with an increased burden from environmental lead pollution. This pollution may come from various sources such as old cars, electrical generators (which are widely distributed in the city), and the presence of a large number of old houses which can be translated into increased BLLs in the general population .

As the present study is a part of an original work to examine lead levels in pregnant women and their infants in the city, data derived from such a study could be used as a baseline indicator for future programs. It is important to have a high confidence in data derived from this survey.

The GM of MBLLs concentration of maternal blood in this study was 3.26 ± 1.91 µg / dl with a range of (0.5 - 22.39 µg / dl), which is lower than reported in Al-Naemi et al. [15] study carried out in 2007 (5.26 ± 3.33 µg / dl) in the same venue. The mean BLL reported by Al-Naemi et al^[15] was for 306 non-pregnant mothers at childbearing age which were taken randomly from women coming to a primary health care center (PHCC) for their children's vaccination. This discrepancy could be explained by three hypotheses:

(1) The sample of the current study is hospital based so probably could not be considered as representative. The sample of Al-Naemi et al.^[15] included females of a childbearing age who attended Al-Hadbaa PHCC. This center has a wide catchment area mostly of moderate and low socioeconomic status. (2) Al-Naemi et al.^[15] in their work, used finger stick samples which may yield higher false measurements than venous blood samples used in the present study, probably due to outside lead contamination and lastly the data of the reported work were not log transformed.

The GM of lead concentration in the umbilical cord recorded by this study was 2.29 ± 2.11 µg/dl with a range of 0.30 - 22.91 µg/dl. This figure was higher than that reported by Kirel et al^[16] in Turkey who recorded a mean UBLL value of (1.65 ± 1.4 µg/ dl). This difference may be due to small sample size in the Kirel et al^[16] study (n= 120). Also it is worth noting that unleaded gasoline, which is widely used in this country may lead to a sub-statistical low level of exposure to lead.

In the present work, lead concentration in the umbilical cord is significantly correlated with, and lower than, the concentration of maternal venous blood (r= 0.856, P= 0.001). This finding is consistent with the findings of other studies^[16-18] which supports the conclusion that the placenta is not a very effective biological barrier and it does not hinder much of the lead transport. Lead freely crosses the placenta, consequently gestational lead is not only harmful to women but also to the developing fetus^[19].

The present work demonstrated that high MBLLs were significantly related to the risk of development of hypertension during pregnancy (OR= 6.84, P= 0.000). This result is similar to the result obtained by Rothenberg et al^[20] who reported an association between blood lead and blood pressure during pregnancy by a cohort study conducted among 1932 pregnant women in South Central Los Angeles.

The particular target tissue for an effect of lead on blood pressure has not yet been established, but several biologic mechanisms have been suggested. The two major modes of action identified are direct effect on end-arterial smooth muscles mediated through distributed calcium metabolism and effects on the rennin-angiotensin axis. In addition, lead may interact with vasoactive agents^[21].

The present study showed that 234 out of 350 pregnant women (66.86%) were anemic. Although iron has been shown to be important in lead absorption, in this study no association between hemoglobin level and concentration of lead in pregnant women was found. This finding is most likely due to the difficulty of measuring iron deficiency anemia in a population undergoing the physiological changes associated with pregnancy^[22].

Birth weight is a strong predictor of survival and of development outcomes in childhood including growth, morbidity, and cognitive performance^[5]. Kaul et al^[23] mentioned that there is an inverse relation between maternal lead burden and birth weight in the offspring of women with relatively low blood lead.

In the current study, it was observed that neonates born to women with BLLs = 10 µg/ dl had an increasing risk of having low birth weight (OR= 43.54, P= 0.000).

The public health significance of this finding is notable, because early growth problems have health and social consequences. It has been shown that the early impaired growth is associated with decreased intellectual and physical performance, such as work capacity, and school achievement^[24]. Lead may impair birth weight through an effect on prenatal bone growth itself in such a way that the attained weight at birth may be negatively affected^[25].

Schnaas et al^[5] mentioned that increased MBLL was associated with decreased birth weight, and lower birth weight was associated with poor postnatal intellectual development, which is the modeled effect of MBLL six to ten years later. Also an intelligence quotient (IQ) could be mediated through lead effect on birth weight, since the third trimester of pregnancy constitutes a critical period for fetal growth and subsequent intellectual child development, during which lead exposure can produce long lasting and possibly permanent effects. In addition there is no threshold for the adverse consequences of lead.
Rahman and Hakeem^[26] in Pakistan found no association of MBLLs with fetal growth neither in terms of birth weight nor in birth length. A small sample size (n= 73) which is not large enough to pick up these association and racial differences in the effect of lead, may explain this apparent lack of association.

A study by Hernandez-Avila et al^[27] evaluated the effect of MBLLs on head circumference of newborns and one month old infants. They concluded that high MBLLs were significantly related to the risk of a low head circumference score . The present work also demonstrated that mothers with high BLL (= 10 µg/ dl) are at risk of having a newborn with a low head circumference measurement (OR= 3.16, P= 0.013). However, Rahman and Hakeem did not confirm this resul^[26].

The present study revealed that only 5.3% of newborns have an Apgar score less than 7. Those were newborns to mothers with high BLLs (=10 µg/ dl). Despite that, no association was demonstrated between MBLLs and Apgar score. Sowers et al.^[28] conducted a study among 705 women aged 14-34 years showed that maternal blood lead concentration and its changes were not associated with reduced Apgar score.

The present study provides, for the first time in the country, data on maternal and UBLLs with a clear significant association between high MBLLs and low birth weight neonates with small head circumference .The following points should be carefully considered in Mosul city :

1. Efforts should be made to reduce BLLs of reproductive age women to minimize transfer of MBLL to fetus and nursing infant. So screening of women at childbearing age for elevated BLLs is needed.

2. General education on measures to reduce lead exposure may be useful for parents. This includes information on potential risk factors for lead exposure and specific prevention strategies that should be tailored for the family and for the community in which care is provided.

3. Future research is needed to evaluate the BLLs among women of child bearing age, since little is known about the cycling of blood lead through generations and the means to reduce the lead burden on women's bodies at child bearing age.

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