Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels are critical in pregnancy for the development of the baby's central nervous system, retinal photoreceptors, and immune system. Consequently, maternal serum FA levels change in the course of pregnancy, depending on foetal requirements. In this context, it is necessary to monitor FA concentration values throughout pregnancy so that deficiency can be detected.
Reference nutrient ranges are the most useful tool to evaluate the adequacy of nutritional status and to identify women who are at risk of an adverse health outcome.
In the little literature that does exist, reference ranges for individualized FA in serum are normally reported in non-pregnant adults. In populations of healthy pregnant women, serum reference values have only been described in a Brazilian cohort of 225 pregnant women and in a Norwegian cohort of 247 pregnant women.
In the Mediterranean population, the composition of the diet is well-known for its low content of SFAs, and high content of MUFAs and n-3 PUFAs, mainly derived from olive oil and fish consumption. Consequently, reference values of circulating FA should be measured in different populations.
FAs can be measured in serum, erythrocyte, or adipose tissue. It is well-recognised that FA levels in serum reflect short-term intake, and are more representative of the current dietary habits of subjects. However, other authors have analysed FAs in the erythrocyte membrane for assessing FA status as it reflects the last 30–60 days of intake so comparisons among studies are difficult.
In previous studies, the analysis of an individual FA may be found expressed either quantitatively or qualitatively as a relative percentage of total FAs. But the authors of the current report note that without standardising the criteria for providing an appropriate reference range, there is a great risk of misinterpretation.
No previous study has reported reference intervals for serum n-6/n-3, AA/EPA, AA/(EPA + DHA) and LA/DHGLA ratios, or the EFA index in pregnant women.
Considering the lack of reference intervals for pregnant women, the aim of the current study was to provide the reference intervals for serum SFA, MUFA and PUFA (n-6 and n-3) in a large population of healthy pregnant women from a Mediterranean country in T1 and T3 of gestation, expressed both as concentrations and as percentages of the total concentration of FA in serum samples. No previous study has reported serum reference ranges in both types of concentration units in healthy pregnant women.
The study also aimed to describe the variation of FA levels in serum according to some maternal factors such as age, obesity, sedentary lifestyle, lower educational level, low diet quality, parity and non-Spanish ethnicity.
The authors note that the percentiles of reference ranges proposed will be a useful tool for assessing the degree of adequacy of FAs in pregnant women, in both individual monitoring of pregnancy, and population-based epidemiological studies.
A prospective study of pregnant women was conducted from T1 to T3 (12 ± 0.5 and 36 ± 0.4 gestational week, respectively). Participants were healthy pregnant women from the ECLIPSES study (n=479) - a randomised, triple-blind clinical trial of different doses of iron supplementation.
Medical, socioeconomic, educational level and lifestyle information were collected. Serum samples were collected at both T1 and T3 (n=476) and a total of 36 FAs were analysed.
Medical, socioeconomic, educational level, and lifestyle information was collected on all participants. The Spanish diet quality index (SQDI) was estimated from nine food groups (protein foods, dairy foods, cereals, fruits, vegetables, oil, legumes, tubers, sweets). A score was obtained ranging from 0 points (low quality diet) to 18 points (high quality diet).
Serum samples were collected in the first and third trimester in order to measure FA levels.
A total of 11 fatty acids were analysed in serum by gas chromatography mass spectrometry and were expressed as absolute (µmol/L) and relative (percentage of total FA) concentration units. Serum concentrations of SFAs, MUFAs, n-6 PUFAs, n-3 PUFAs, various FA ratios, and the EFA index were determined. The reference intervals (2.5/97.5 percentiles) in absolute values from T1 ranged from 1884.32 to 8802.81 µmol/L for SFAs, from 959.91 to 2979.46 µmol/L for MUFAs, from 2325.77 to 7735.74 µmol/L for n-6 PUFAs, and from 129.01 to 495.58 µmol/L for n-3 PUFAs.
Serum FA profile changed from T1 to T3: Σtotal SFA, Σtotal MUFA and Σtotal n-6 PUFA increased during pregnancy, whereas essential FAs such AA and EPA decrease and DHA remains unchanged
The women with obesity, sedentary lifestyle, lower educational level and those of non-Spanish ethnicity had higher levels of total SFA, total MUFA and AA, and lower levels of total n-3 PUFA and DHA. Factors such as obesity and sedentary lifestyle, could favour the presence of proinflammatory FAs such as AA.
The report states: "Overall, it is important to note that lifestyle, sociodemographic and genetic factors can affect normal FA reference intervals in pregnancy. Therefore, serum FA measure could be considered as an integration of dietary intake and individual biological response. Consequently, absolute percentiles of FAs for 95% of the population could assist the evaluation of FA status and the identification of women at risk of either under exposure (≤2.5% percentile) or over exposure (≥97.5% percentile) to an individual FA...
"Every region must provide their own reference ranges in accordance with the characteristics of their population. Further research is needed to identify the personal and environmental factors that contribute to a healthy diet during pregnancy."
Martín-Grau, C.; Deulofeu, R.; Serrat Orus, N.; Arija, V.
"Trimester-Specific Reference Ranges for Saturated, Monounsaturated and Polyunsaturated Fatty Acids in Serum of Pregnant Women: A Cohort Study from the ECLIPSES Group"