To develop an activity questionnaire for objective and rapid assessment of maternal habitual physical activity with the aim of describing its relationship with birth size.

Prospective observational study.

Six villages near Pune, Maharashtra, India.

Seven hundred and ninety-seven rural Indian mothers were studied after excluding abortions and termination of pregnancies, foetal anomalies, etc.

Principal components analysis (PCA) was used to identify a few leading questions from an elaborate questionnaire involving 36 questions related to 14 typical maternal activities.

On the basis of high loading (>0.8), PCA identified three activities, i.e. farming, fetching water and washing clothes. Questions and sub-questions related to these activities only were considered for defining an activity score for rapid assessment. Validation of this new activity score, with the score based on the elaborate questionnaire, showed 70% sensitivity as well as specificity. New activity scores showed strong inverse relationships similar to those observed using the elaborate questionnaire, at early as well as late gestation, with neonatal head circumference (P=0.001 and 0.055) and mid-arm circumference (P=0.02 and 0.03).

Simple questionnaires, based on leading activities identified by PCA, can be as informative as longer and detailed questionnaires. This method has potential for adaptation, especially in rural communities in developing countries.