Preterm Labor and Eating Fish Abstract & Commentary

By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.

Dr. Hobbins reports no financial relationship to this field of study.

Synopsis: A sub-analysis of data from a randomized trial assessing the possible benefit of omega-3 supplementation to prevent preterm labor shows a protective effect of consuming fish 1 to 3 times per week in patients who have had previous preterm births.

Source: Klebanoff MA, et al. Fish consumption, erythrocyte fatty acids, and preterm birth. Obstet Gynecol 2011;117:1071-1077.

Dealing with a question about certain dietary items in pregnancy sometimes is daunting because often there is no consensus regarding a proper answer. Here is a study that may help to answer a recurrent question involving fish.

The concept has been circulating that consumption of omega-3 fatty acids can result in a reduction of preterm birth (PTB), so the NICHD Perinatal Network undertook a randomized trial to see if omega-3 supplementation really did improve outcome in patients who have had at least one prior PTB.2 Interestingly, although the results suggested no obvious benefit from the supplement, data collected during the trial allowed the investigators to look at the relationship of fish consumption, in general, to PTB.1

Patients were enrolled at 16 to 21 weeks of gestation, and all had had at least one PTB. All of these patients were on weekly injections of 17 P. At the initial interview, the investigators asked about their consumption of red meat, fish, canned tuna, and shellfish, and the data were analyzed according to how many servings per week they ate. (For example, < 1 serving/month, 1-3 servings/week, > 3 servings/week, etc). The investigators also analyzed levels of various erythrocyte fatty acids at the time of entry. The primary outcome was the incidence of preterm birth, defined as < 37 weeks.

The randomized study included 852 patients and the findings were fascinating. The 253 (29.7%) whose fish consumption was < 1 serving per month had a PTB rate of 48.6%. The 524 who ate fish 1-3 times per week and the 75 with > 3 times per week consumption, together, had a PTB rate of 35.9%. This represented a statistically significant difference. However, the association was nonlinear, resulting in a "u" shaped curve in which there was an increase in PTB after consumption exceeded 3 servings per week. For example, the odds ratio (OR) of PTB in those with 1-3 week consumption was 0.60 (compared to those with low fish consumption), but the OR rose to 1.25 with consumption 7 times per week, and 1.93 with 8 servings a week.

Erythrocyte omega-3 levels were higher with greater fish consumption, and the lowest PTB rate was in the group whose omega-3 levels were in the second quartile. As reported in the original paper,2 the addition of omega-3 supplementation had no effect on the rate of PTB, and the newest paper from the group1 showed that this non-effect was irrespective of the erythrocyte omega-3 levels or the amount of fish consumed.


This study implies that eating fish 1 to 3 times a week can diminish PTB in those who are at greatest risk. The suggestion that some fish is good, but more (> 6 times per week) could be detrimental, is puzzling. However, this trend also was noted in a study from Finland,3 where the population is known for its fish consumption. So, maybe there is something to the idea that mercury and/or polychlorinated biphenyls (PCBs) sometimes found in pelagic fish (such as tuna) can be associated with adverse pregnancy outcome when consumed in large amounts. The authors also point out that fish are a great source of protein, and that an old study (1980) showed high protein supplementation actually increased PTB in a randomized study undertaken in Harlem.4

Why would eating fish work to decrease PTB, while omega-3 supplementation did not accomplish the same result? Perhaps since the supplements were not started until the late second trimester in the study; they need to be on board in the first trimester. Another thought is that the protective factor in fish is something other than omega-3 fatty acids.

Too much protein, too little protein, too much fish, too little fish — what is the pregnant patient to do? I suppose one could roll out the old platitude "everything in moderation," and with fish, that means 1 to 3 servings per week (at least in those with a history of previous PTB).


  1. Klebanoff MA, et al. Fish consumption, erythrocyte fatty acids, and preterm birth. Obstet Gynecol 2011;117:1071-1077.
  2. Harper M, et al. Omega-3 fatty acid supplements to prevent recurrent preterm birth: A randomized controlled trial. Obstet Gynecol 2010;115:234-242.
  3. Olsen SF, et al. Duration of pregnancy in relation to seafood intake during the early and mid-pregnancy: Prospective cohort. Eur J Epidemol2006;164:1203-1209.
  4. Rush D, et al. A randomized controlled trial of prenatal nutritional supplements in New York City. Pediatrics 1980;65:683-697.