Seasonal Differences in Birth Weights and Lengths Depends on Exposure During Pregnancy in Rural India
Authors: Madan Emily M , Haas Jere D , Menon Purnima , Kumar Vishwajeet , Kumar Aarti , Singh Shambhavi , Dixit Swati 
Published: November 2023

Background

Birth weight and birth length are important indicators of morbidity, mortality and future growth and development during childhood and adulthood. The seasonality of these indicators has been documented in various developing countries, but there is a dearth of data from rural South Asia. Seasonal variations in anthropometry are generally attributed to seasonal deteriorations in maternal health and nutritional status that occur during pregnancy when food supplies are diminished, and both agricultural labor demands and risk for infectious disease are high. Peak fetal growth velocity in length and weight occur during the 2nd and 3rd trimester of pregnancy, respectively, and are thus periods when fetal growth may be particularly vulnerable to seasonal insults.

Objective

To describe seasonal variation in birth weights and lengths that result from exposure to one of three seasons during the 2nd and 3rd trimesters of pregnancy, respectively, for length and weight.

Methods

From August 2015–September 2016, all pregnant women in the 32nd week of gestation or later, residing in 9 rural villages in Uttar Pradesh (UP) were invited to participate in a study of infant growth. Pregnant women were identified from a pre‐existing registry that was based on a bi‐monthly village surveillance of missed menstrual cycle. The final working sample of singleton, full‐term newborn infants with valid anthropometry measured within 14 days of birth was 288 for weight and 254 for length. Seasons were defined as rainy (July–September), winter (October–February) and summer (March–June). Multi‐level models with village as a random effect were used to test the effect of exposure to season during the 3rd trimester for weight, and the 2nd trimester for length.

Results

The mean (SD) birth weight of the sample was 2.64 (0.44) kg, and the mean (SD) birth length was 48.0 (1.6) cm. Mean birth weights for infants born in the rainy, winter and summer season were 2.66 (0.44) kg, 2.59 (0.45) kg and 2.75 (0.38) kg, respectively. Mean birth lengths for infants born in the rainy, winter and summer season were 48.2 (1.4) cm, 47.8 (1.6) cm and 48.1 (1.8) cm, respectively. After controlling for gestational age and sex, infants exposed to the rainy season during the 3rd trimester of pregnancy had mean birth weights that were 163 grams lower than infants exposed to summer (p=0.022). Infants exposed to the rainy season during the 2nd trimester of pregnancy had birth lengths that were 0.6 cm (p=0.068) and 0.5cm (p=0.062) lower than in winter and in summer, respectively.

Conclusions

These preliminary findings suggest that observed seasonal differences in newborn size vary according to season of exposure during periods of expected maximum fetal growth velocity in weight and length. Further analyses will seek to understand the seasonality of maternal health, nutrition security and physical activity that may explain seasonal patterns in birth weights and lengths.

Support or Funding Information

Agriculture for Nutrition and Health (A4HN), Leveraging Agriculture for Nutrition in South Asia (LANSA)