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Scientific Evidence Supporting the Use of
Omega-3 Fatty Acids to Prevent Preterm Labor
The most significant predictor of infant health is
gestational age at birth. Pregnancies of longer duration are always preferable
to preterm labor. Certain prostaglandins normally produced in the human body
(especially PGF2 and PGE2) are partially responsible for initiating labor at the
end of pregnancy. Often, when labor begins too early (at less than 37 weeks
gestation) the reason is not identified. Recent studies have shown, though,
that shifting the balance of prostaglandins in the body away from those that
contribute to labor has a significant effect on prolonging the duration of both
complicated and uncomplicated labors. While this increase in pregnancy duration
may be only a few days, an increase of even a few days or one week can result
in a dramatic improvement in infant outcome.
It has been recognized that infant birthweights in Northern
European countries are significantly higher than in other areas of the world,
including the United States. This increase in birthweight is largely
attributable to longer gestations. Because these populations consume a diet
that is very high in fatty marine fish, it was hypothesized by multiple
researchers more than two decades ago that the higher concentration of omega-3
fatty acids in the Northern European diet has a positive effect on prolonging
the duration of pregnancy.
Over the course of the past two decades, many studies on
both animals and humans, and both European and North American populations, have
shown that omega-3 fatty acids, whether from dietary sources or other
supplementation, cause a significant increase in the duration of pregnancy.
Reece et al. Showed in 1997 that the level of omega-6
metabolites (arachidonic acid and docosapentaneoic acid) was significantly
higher in the blood and placenta of mothers who delivered preterm1.
These metabolites are produced by competition of omega-3 FAs and omega-6 FAs for
the same enzymes. When omega-3 FA levels are lower than omega-6, more omega-6
FA metabolites are produced. Thus, higher levels of omega-6 metabolites in
these preterm mothers correlated to a lower relative amount of omega-3 FAs in
their blood stream.
Other studies have experimented with the results of
supplementing a woman’s diet with a source of omega-3 FAs, usually in the form
of fish oil capsules (because they are convenient to standardize dosing). Olsen
et al. showed in one study that the rate of preterm delivery was decreased to 21%
in women supplemented with fish oil who had had a previous preterm delivery2.
Similar women who received placebo capsules in this study had a preterm delivery
rate of 33%. This difference was significant. Olsen et al. later showed a
significant increase in the duration of pregnancy in women who were either
supplemented with fish oil capsules3 or who had higher dietary
omega-3 FA intake4. In these two separate study populations, fish
oil supplementation and increased dietary omega-3 FA intake groups had an
average of 4.0 days and 5.7 days longer pregnancies, respectively. These
results were both significantly different from controls.
A randomized trial of docosahexaenoic acid (DHA)
supplementation during the third trimester of pregnancy was Published in 2003 by
The American College of Obstetricians and Gynecologists. Smuts et al.
found the duration of gestation to increase significantly with increased DHA intake during
the last trimester of pregnancy5.
Subjects were enrolled
between the 24th and 28th week of pregnancy and consumed high-DHA eggs until
delivery. Gestational age was increased by 6 days in the higher DHA group. The increase in duration of
gestation noted here is similar to the increases that have been found in two
studies of women with already high background intakes of docosahexaenoic acid
and eicosapentaenoic acid assigned to consume an additional 2.7 g of n-3 long
chain polyunsaturated fatty acids per day. This suggests that relatively
modest amounts of approximately 100 mg of dietary DHA per day during pregnancy may be sufficient to extend
gestational age. Furthermore, it was discovered that birth weight,
length, and head circumference increased, although not significantly5.
However, these findings could indicate that intrauterine growth was enhanced,
and would be an interesting topic for future studies.
There has even been an animal study that showed an ability
of omega-3 FA infusion to stop labor in two sheep that were actively contracting6.
While further studies are obviously necessary, this result is exciting as it
even suggests that omega-3 FAs may have a future therapeutic role in stopping
preterm labor once it has already begun.
While there are some studies that have failed to show a
significant increase in pregnancy duration, birthweight or any other factor
after increased omega-3 FA intake, these studies do not show an adverse effect
of the treatment, and they may suffer from design flaws. One such study by
Onwude et al. failed to show any differences in pregnancy outcomes between
omega-3 supplemented and control groups. Authors of this study reported a very
low (<50%) compliance rate in both groups7. This is one possible
explanation for the lack of effect shown in some study results.
Overall, compelling evidence is mounting in support of a
protective role for omega-3 FA supplementation in pregnancy to prolong gestation
and decrease preterm labor rates. This result would translate into higher
infant birthweights. The logical result would likely be to decrease newborn
morbidity and mortality. Using omega-3 FA supplements or increasing dietary
omega-3 FA intake are both good strategies to increase pregnancy duration and
prevent preterm labor.
Bibliography
1.
Reece MS, McGregor JA, Allen KGD, Harris MA. Maternal and perinatal
long-chain fatty
acids: possible roles in preterm birth.
American Journal of Obstetrics and Gynecology
1997;176:907-914
2. Olsen
SF, Secher NJ, Tabor A, Weber T, Walker JJ, Gluud C.. Randomised clinical trials
of
fish oil supplementation in high risk pregnancies. British Journal of Obstetrics and
Gynecology
2000;107:382-395
3. Olsen
SF, Sorensen JD, Secher NJ, et al. Randomised controlled trial of effect of
fish oil
supplementation on pregnancy duration. The Lancet 1992;339:1003-1007
4.
Olsen SF, Hansen HS, Sommer S, et al. Gestational age in relation to
marine n-3 fatty acids in
maternal erythrocytes: a study of women in the Faroe Islands and Denmark. American
Journal of Obstetrics and Gynecology
1991;164:1203-1209
5.
Smuts CM, Huang M, Mundy D, Plasse T, Major S, and Carlson SE. A
Randomized Trial of Docosahexaenoic Acid
Supplementation During the Third Trimester of Pregnancy. American
Journal of Obstetrics and Gynecology 2003;101:469-79.
6. Baguma-Nibasheka
M, Brenna JT, Nathanielsz PW. Delay of preterm delivery in sheep by
omega-3 long-chain polyunsaturates. Biology of Reproduction 1999;60:698-701
7. Onwude
JL, Lilford RJ, Hjartardottir H, Staines A, Tuffnell D. A randomised double
blind placebo
controlled trial of fish oil in high risk pregnancy. British Journal of
Obstetrics and Gynaecology
1995;102:95-100
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