Preterm birth and low birth weight may be reduced with combined vitamins and fish oil

Pregnant women are advised to take folic acid (vitamin B9) and vitamin D to support fetal growth and neurological development. However, fish oil has received less attention, despite its content of the omega-3 fatty acids EPA and DHA, which play a crucial role in the development of the brain, vision, and numerous metabolic functions.
New evidence now suggests that supplementation with fish oil alongside the recommended prenatal vitamins may reduce the risk of preterm birth and low birth weight. These findings come from a study published in Frontiers in Nutrition. In addition, fatty fish and fish oil supplements appear to offer other benefits for maternal mood and fetal health.

Pregnant women are advised to take 400 micrograms of folic acid (vitamin B9) daily, as it supports the development of the fetal nervous system and helps prevent malformations of the brain and spinal cord. In addition, a daily supplement of at least 10 micrograms of vitamin D is recommended, as it contributes to the development of the baby’s bones, immune system, and many other functions.
Although health authorities recommend these vitamin supplements, they do not yet routinely recommend fish oil despite the well-established role of the omega-3 fatty acids EPA and DHA in building all cell membranes and supporting the development of the baby’s nervous system, brain, and vision. There is also evidence that omega-3 fatty acids reduce the risk of preterm birth.
Even so, omega-3 deficiency is widespread, partly because many people, including pregnant women, consume too little fatty fish. It has remained unclear whether fish oil supplementation, when combined with the recommended vitamins, provides additional benefits during pregnancy and fetal development. The aim of this new study was therefore to investigate this question in greater detail.

Fish oil benefits pregnancy and fetal growth in multiple ways

The researchers analyzed data from a large population-based study known as the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b), which included 9,461 healthy pregnant women from across the United States. Participants were followed throughout pregnancy and delivery, and their intake of vitamins and other supplements was recorded through interviews and study visits.
The researchers then compared pregnancy outcomes, delivery, and birth weight between participants who took only the recommended vitamins and those who combined vitamin supplementation with fish oil.
After adjusting for various factors, the study found that the combination of vitamins and fish oil was associated with the following benefits compared to vitamins alone:

• A significantly lower rate of preterm birth
• A significantly lower rate of low birth weight

The researchers also note that combining vitamins with omega-3 fatty acids during pregnancy may have additional benefits due to various biological interactions. Omega-3 fatty acids EPA and DHA are involved in numerous physiological processes, including the regulation of inflammatory responses, circulation, and improved placental function—such as more efficient transport of EPA and DHA to the fetus.
The fetus’s need for these omega-3 fatty acids is particularly high during the later stages of pregnancy, when the brain and lungs undergo rapid growth and development. These mechanisms may help explain the positive effects of omega-3 fatty acids on pregnancy outcomes, normal fetal growth, and full-term delivery.
According to the researchers, this study adds to a growing body of evidence suggesting that pregnant women should consider taking fish oil supplements in addition to the recommended vitamins.

• Pregnant women should choose smaller fatty fish such as herring, anchovies, mackerel, and wild salmon, which are lower on the food chain. Larger fish like tuna are not recommended
• Fish oil supplements should be purified to remove environmental contaminants and should be of high quality

Fish oil during pregnancy may also help prevent other complications and conditions

On this website, we have previously covered studies showing that fatty fish and fish oil supplementation during pregnancy may also help reduce the risk of postpartum depression, miscarriage, childhood asthma, and other complications. You can read more about this here:

• The widespread lack of omega-3 among pregnant women has serious consequences

• Compounds in fish oil can prevent miscarriage and preterm delivery

• Fish oil from oily fish or supplements protects children against asthma

Reference:

William Yakan et al. Omega-3 supplementation in addition to prenatal vitamins during pregnancy is associated with lower rates of preterm birth and small for gestational age. Frontiers in Nutrition 2026