CONCEPTUAL FRAMEWORKS
9.3 HOLDING A DEFAULT VIEW
This observational cohort study carried out among pregnant women at the Lagos University Teaching Hospital examined how a substantially low value of maternal serum cholesterol levels in early pregnancy which represents a relatively normal peri-conceptional cholesterol level that failed to rise as expected in the second trimester, would affect later events, such as week of delivery and fetal growth.
The data analysis in the study was performed with the strict exclusion of known potential confounders that may substantially influence risk of preterm delivery and low birth weight (impaired fetal growth).
There was a weak but statistically significant relationship between low total cholesterol and the lower socioeconomic class when compared to women with mid-range total cholesterol. These indicate that,
micronutrient deficiencies may be more common among the low-total cholesterol risk group studied here and could account for the
observed adverse outcomes. Many such nutritional deficiencies have been studied as predictors of preterm delivery or low birth weight120,
121.
The incidence of preterm delivery in this highly selected study cohort (8.7%) was only slightly higher than that quoted in the study by Edison et al (6.6%)110 but it is still within the range quoted by Kierse at 5-10%10 and from a study done in a regional tertiary hospital in Nigeria by Ezechukwu et al (5-25%) 67. This was probably due to the similarities in the study groups used in all these studies especially with regard to the patients’ age range.
Test of the association of Low maternal serum cholesterol with preterm delivery showed statistically significant elevation of risk in analysis that compared mothers with low-total cholesterol with mothers with mid-total cholesterol (11.8% versus 2.2%, 4.83 folds
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increase risk). This finding supported the study done by Edison et al which reported a prevalence of preterm delivery among mothers with low total cholesterol as 12.7%, compared with 5.0% among control subjects with mid–total cholesterol, thus representing a 2.93 folds increase risk110. This association was observed only among white mothers. However, this present study showed that the association also exists among the black Nigerian mothers. The possible explanation may lie in the control study population which included both women with mid-range and high total cholesterol levels in the Edison’s study while only women with mid-range total cholesterol were used in this present study thus increasing the likelihood of having more women in the low total cholesterol group compared to the control group.
Preterm delivery is known to be initiated by multiple
mechanismshttp://www.ncbi.nlm.nih.gov/pubmed/1817777820, 26 but data on hyperlipidemia in women who deliver preterm is limited. Various reports have suggested a possibly increased risk for prematurity with very high maternal cholesterol122. Finding by Catov and co-workers123 showed that an elevation in maternal non-fasting plasma triglyceride or cholesterol level early in gestation was associated with a greater than 2-fold increased risk of preterm delivery. This was corroborated by the finding from this present cohort study which reported an elevated risk of 3.33 folds for preterm birth among mothers with high maternal cholesterol (greater than 239mg/dL).
Low birth weight (LBW), which is the single most powerful predictor of mortality in the first few months of life51, was reported to occur in 14.4% of the term born infants in this study. This is only slightly higher than the year 2000 estimate of 10.0% among new born infants at term in developing countries60 but slightly lower than the reported incidence in the developing countries including Nigeria throughout the 1990’s which remained at 16%54, 61.
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The working hypothesis for this study that the risk for low birth weights would be increased among infants who are born to mothers with low maternal serum cholesterol was also confirmed statistically;
the statistical trend estimated a two-fold increase in risk in mothers with low total maternal cholesterol compared to control mothers with midrange cholesterol. This was consistent with the reported risk from the study by Edison et al112, however, there was a shift toward lower birth weights still within the reference range among term infants who were born to mothers with low maternal serum cholesterol in their study, which was in variance to the data from this present study
where the average birth weight among these women with low maternal serum cholesterol was actually below 2500g (2348.0-g).
The present cohort study also showed a positive correlation of high maternal total cholesterol with reduced birth weights which is
consistent with the finding by Fakhar-un-Nisa et al114 in a prospective analytical study involving 100 Pakistani pregnant women
(non-diabetic and non-hypertensive) at 24-36 weeks of pregnancy which reported a positive correlation between maternal cholesterol levels and neonatal low birth weight. The average birth weight difference was higher among the low total cholesterol group (225.5-g) than among the high total cholesterol group (124.5-g) when compared to the control mid-range cholesterol group. This suggests the possible critical role of micronutrient deficiencies being commoner among the low-total
cholesterol risk group studied which could greatly account for this observed difference.
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