TY - JOUR

T1 - Secular trends in seasonal variation in birth weight

AU - B. Jensen, Camilla

AU - Gamborg, Michael

AU - Raymond, Kyle

AU - McGrath, John

AU - Sørensen, Thorkild I.A.

AU - Heitmann, Berit L.

N1 - Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

PY - 2015/6

Y1 - 2015/6

N2 - BACKGROUND: Many environmental factors have been shown to influence birth weight (BW) and one of these are season of birth.AIM: The aim of the present study was to investigate the seasonal variation in BW in Denmark during 1936-1989, and to see if the variation could be explained by sunshine exposure during pregnancy.METHODS: The study population was selected from the Copenhagen School Health Records Register and included 276 339 children born between 1936 and 1989. Seasonal variation was modeled using a non-stationary sinusoidal model that allowed the underlying trend in BW and the amplitude and phase of the yearly cycles to change.RESULTS: There was a clear seasonal pattern in BW which, however, changed gradually across the study period. The highest BWs were seen during fall (September - October) from 1936 to 1963, but a new peak gradually grew from the early 1940s during early summer (May - June) and became the highest from 1964 to 1989. The amplitude of the fall peak started at 25.5 (95%CI 24.6; 25.9) grams and gradually disappeared. The amplitude of the early summer peak gradually arose from nothing to a peak of 18.6 (95%CI 17.7; 19.6) grams in the mid 1980s where it started to decrease again. Sunshine did not explain the seasonal variation in BW.CONCLUSION: There was a clear seasonal pattern in BW in Denmark 1936-1989, which however changed across the study period. Throughout the study period we observed a peak in BW during the fall, but gradually, starting in the early 1940s, an additional early summer peak emerged and became the highest from 1964 and onwards.

AB - BACKGROUND: Many environmental factors have been shown to influence birth weight (BW) and one of these are season of birth.AIM: The aim of the present study was to investigate the seasonal variation in BW in Denmark during 1936-1989, and to see if the variation could be explained by sunshine exposure during pregnancy.METHODS: The study population was selected from the Copenhagen School Health Records Register and included 276 339 children born between 1936 and 1989. Seasonal variation was modeled using a non-stationary sinusoidal model that allowed the underlying trend in BW and the amplitude and phase of the yearly cycles to change.RESULTS: There was a clear seasonal pattern in BW which, however, changed gradually across the study period. The highest BWs were seen during fall (September - October) from 1936 to 1963, but a new peak gradually grew from the early 1940s during early summer (May - June) and became the highest from 1964 to 1989. The amplitude of the fall peak started at 25.5 (95%CI 24.6; 25.9) grams and gradually disappeared. The amplitude of the early summer peak gradually arose from nothing to a peak of 18.6 (95%CI 17.7; 19.6) grams in the mid 1980s where it started to decrease again. Sunshine did not explain the seasonal variation in BW.CONCLUSION: There was a clear seasonal pattern in BW in Denmark 1936-1989, which however changed across the study period. Throughout the study period we observed a peak in BW during the fall, but gradually, starting in the early 1940s, an additional early summer peak emerged and became the highest from 1964 and onwards.

U2 - 10.1016/j.earlhumdev.2015.03.010

DO - 10.1016/j.earlhumdev.2015.03.010

M3 - Journal article

C2 - 25916263

VL - 91

SP - 361

EP - 365

JO - Early Human Development

JF - Early Human Development

SN - 0378-3782

IS - 6

ER -