Higher First-Trimester Protein Intake Linked to Lower Risk of Small Birth Size: Study

More protein isn't always better-when it comes to pregnancy, the "sweet spot" may matter more than the extra scoop.

Getting the right amount of protein during early pregnancy—not necessarily the highest amount—may be linked to a lower chance of delivering a small-for-gestational-age (SGA) baby, according to a new secondary analysis published in Nutrients.

Researchers analyzed data from 7,067 first-time pregnant women enrolled in the U.S.-based Nulliparous Pregnancy Outcomes Study. Participants completed a food frequency questionnaire during the first trimester (6–13 weeks), allowing researchers to estimate daily protein intake.

Women were grouped into four protein intake categories: less than 0.6 g/kg/day, 0.6 to less than 0.8 g/kg/day, 0.8 to less than 1.1 g/kg/day, and 1.1 g/kg/day or higher. Researchers adjusted the findings for factors including age, body mass index (BMI), education, income, insurance status, chronic hypertension, and total calorie intake.

The results showed that women consuming 0.8 to less than 1.1 g/kg/day had 22% lower adjusted odds of giving birth to an SGA infant compared with those consuming 1.1 g/kg/day or more.

However, the researchers caution that the finding should be interpreted carefully. There was no clear dose-response relationship, the lower-protein groups did not differ significantly from the highest-intake group, and sensitivity analyses using absolute protein intake failed to reproduce the association. This means the study does not identify an ideal protein target or prove that changing protein intake prevents SGA.

The study also found no significant association between maternal protein intake and gestational diabetes, hypertensive disorders of pregnancy, or large-for-gestational-age births.

Researchers note that protein intake varied across socioeconomic and demographic groups, with lower intake more common among women with lower income and education levels. They say future studies should examine protein sources—such as plant versus animal protein—and track dietary changes throughout pregnancy to better understand how maternal nutrition influences fetal growth.

REFERENCE: Rosas-Rogers, S., Anguzu, R., Hernandez, A. M., et al. (2026). Association Between Maternal Protein Intake and the Risk of Adverse Pregnancy Outcomes. Nutrients. DOI: 10.3390/nu18152543