The cause is largely hormonal. Rising levels of estrogen and progesterone increase blood flow to the mucous membranes throughout the body, including those lining the nasal passages. As these tissues swell, they can lead to congestion, sneezing, and post-nasal drip—without any signs of infection.

The paper would likely find a spike in congestion symptoms between weeks 7 and 10, correlating with the peak of the corpus luteum’s hormone production before the placenta fully takes over.

The paper would open by defining . While often associated with the third trimester, clinical evidence suggests onset frequently occurs in the first trimester (weeks 6–12).

"More Than Just a Stuffy Nose: A Prospective Cohort Study on the Etiology, Impact, and Management of Early Pregnancy Rhinitis"

This section explores the biological mechanisms behind the "stuffy nose," proposing a dual-mechanism theory: