The current descriptive cross-sectional research measured the DHA level in mothers' breast milk with preterm delivery and its effect on common neonatal complications in premature babies. Regarding the impact of maternal diet on the level of free fatty acids such as DHA in breast milk, the measurement of this valuable nutrient in breast milk is important. Changing the maternal or neonatal diet or supplementation resulted in an increasing level of DHA in breast milk. Eventually, this resulted in neonatal circulating with an improvement in the neonatal outcome, especially neurodevelopmental and visual acuity. Despite the infrequent seafood intake in Iranian families and regardless of maternal diet, our research revealed that the mean level of DHA in the breast milk of mothers was in the acceptable range: 0.32% of total fatty acids with the minimum and maximum levels of 0.09% and 0.73%, respectively, in comparison with a worldwide global average level of 0.296 ± 1.27% (
17). In research by Fu et al., the mean level of DHA in breast milk was 0.37% of total fatty acids. In this study, Asian mothers had the highest level of DHA, and mothers in low-income countries had a higher level of DHA in breast milk than those in other countries (
18).
The level of DHA in breast milk did not reveal statistically significant relationships with birth weight, gestational age, postnatal age, delivery mode, age of mother, socioeconomic level of the family, and common neonatal complications such as BPD, IVH, and NEC. Oxidative stress following normal vaginal delivery changes the level of LCPUFA and DHA in the breast milk of mothers. As the findings of many studies show, the mode of delivery affects the level of breast milk DHA. However, the current study showed no significant difference between NVD and C/S in the level of breast milk DHA (P value = 0.32) (
19).
In research by Lapillonne et al., the level of breast milk DHA was decreased during the first month of delivery, and they suggested the fortification of breast milk by DHA supplementation for compensating for this deficiency (
20). In our research, the sampling time was different in patients and the mean age of neonates at the time of sampling was nine days (2 - 44 days). Although in our research, there was no significant relationship between the time of sampling and DHA level, similar to the Lapillonne et al.’s study, Martin et al.’s study showed that as the baby grows, the amount of DHA decreases, and the low levels of DHA were associated with the increased rate of BPD. In contrast to research by Smith and Rouse, DHA supplementation raised the rate of BPD in preterm infants (
10,
20-
22).
The current study showed that newborns with more growth in head circumference, height, and body weight had higher levels of DHA in the breast milk of their mothers, although there was no statistically significant relationship between growth indices and DHA levels. Research by Much revealed that LCPUFA of breast milk improved fat mass growth of infants in the first year of life, and the increased protein and amino acid ratio of breast milk caused better growth indicators (
23).
Despite the wide range of maternal diets, the same level of DHA in the breast milk of mothers with different socioeconomic levels was detected. The intake of food rich in DHA did not correlate with the level of DHA in breast milk. Some research revealed the positive effect of breast milk DHA on decreasing BPD incidence in preterm babies (
24-
26).
The finding of our research revealed the higher growth rate of weight, height, and head circumference in neonates fed by a higher level of DHA in breast milk, although not significantly. In research by Smuts et al. in a clinical trial, supplementation of the maternal diet with DHA during pregnancy made no significant change in the birth weight of neonates (
26). The results of Oken et al. and Halldorsson et al. in the United States confirmed the mentioned results. They indicated that supplementation with DHA did not correlate with babies' weight gain and growth index (
27,
28).
Contrary to research by Ramakrishnan et al. and Olafsdottir et al., supplementation with DHA improved the fetal weight gain in pregnancy (
29,
30). In research by Olsen, the weight gain of neonates with the intake of fish oil was higher than that of the control group (
31).
In a study by Davoodabadi Farahani and Seyyed Zadeh Aghdam in Arak, Iran, intending to detect the effect of DHA and eicosapentaenoic acid (EPA) in pregnancy on birth weight and duration of pregnancy, there was a statistically significant difference between mothers receiving DHA supplementation and the control group. They found 284 g reduced birth weight in neonates of mothers but no effect on the duration of pregnancy in the group with DHA supplementation (
32). They concluded that this negative effect was due to the difference between monitoring the growth index and the guideline of supplementation with DHA.
The current study did not show any difference in gestational age based on the DHA level of breast milk. In research by De Dooy et al., the levels of breast milk unsaturated fatty acids were increased with increasing gestational age (
24).
Two clinical trials revealed the correlation between the omega-3 intake of mothers and the duration of pregnancy so that the duration of pregnancy was prolonged with DHA supplementation in the maternal diet. Olsen et al. detected the longer duration of pregnancy as 2.5% in mothers with fish oil supplementation (
26,
31). A systematic review by Kar et al. in 2016 revealed a 58% decrease in preterm deliveries of less than 34 weeks and a statistically significant relationship between gestational age and supplementation with DHA in pregnancy (
33). In the research by Olsen et al. and Davoodabadi Farahani and Seyyed Zadeh Aghdam, there was no significant relationship between the duration of pregnancy and DHA, EPA, and fish oil supplementation in pregnancy (
31,
32).
The inability of preterm neonates to process fatty acids and produce DHA, the low transplacental transfer rate of this fatty acid from the mother, and low intake of this material after birth due to feeding problems are the concerning issues in this regard (
34). The administration of intralipids solutions during NICU admission may be an inadequate source of DHA to meet the baby's needs (
21,
35). Regarding the mentioned factors, the enrichment of breast milk with DHA seems logical.
Regarding the contribution of inflammatory reactions as an underlying risk factor for neonatal complications such as NEC, BPD, and ROP, DHA with anti-inflammatory properties can decrease the incidence of these complications of prematurity. A longitudinal study by Martin et al. showed the decreased level of DHA in the first months of life concurrent with the progression and severity of chronic lung disease (
21). In research by Martin et al., a 1% decrease in DHA from a total of long-chain fatty acids increased the probability of chronic lung disease by 2.5 times (
21). Many published studies confirmed the reverse correlation between DHA levels and incidence of BPD in preterm babies (
25,
36).
The findings of a clinical trial by Bernabe‐Garcia et al. in Mexico to evaluate the effect of oral DHA with a dose of 75 mg/kg on the severity of ROP showed the positive prophylactic effect of this material on the incidence and severity of ROP (
37). Our research evaluated just the effect of breast milk DHA on neonatal complications, with no pharmacological intervention. Similar to the research of Bernabe-Garcia et al., in research by Bernabe in 110 preterm neonates with a birth weight of 1000 - 1500 g, the incidence and severity of ROP were decreased with DHA supplementation (
38). In a clinical trial by Collins et al. in Australia, supplementation with DHA with a dose of 60 mg/kg/day in preterm neonates with gestational age lower than 29 weeks did not improve BPD progression (
22).
In a study by Fares et al. in Tunisia, supplementation with DHA decreased mortality related to sepsis, IVH, and respiratory distress syndrome (
39). However, our research did not show any positive effect of breast milk DHA on neonatal mortality. The single laboratory measurement of this nutrient of breast milk is the most significant limitation of our research, which limited the study results.
The limitations of our research were the low sample size of the study, financial constraints (due to the high cost of laboratory exams), and the measurement of breast milk DHA just in one sample of breast milk and at different times after delivery (2 - 44 days post-delivery). For more conclusive results, larger studies with more sample size and repeated measurements of breast milk DHA or supplementation of the maternal or neonatal diet with this valuable nutrient is recommended.
The current study's findings showed the acceptable levels of DHA in the breast milk of mothers with preterm delivery, although it did not reveal a significant correlation between maternal and neonatal factors and neonatal outcomes. The low sample size and evaluation of just one breast milk sample can justify no significant effects observed. Regarding the well-known beneficial effects of breast milk, research with a higher sample size and repeated measurements of DHA is recommended.