Exposure to caffeine in adults is mainly through the consumption of coffee.1 The half life of caffeine is 2.5 to 4.5 hours in non-pregnant women but longer during pregnancy, especially in late pregnancy. Caffeine is rapidly absorbed from the digestive system and passes freely across the placenta.2 In addition, fetuses do not metabolise caffeine well.3 Caffeine increases the levels of circulating catecholamines,4 which may cause uteroplacental vasoconstriction and fetal hypoxia, all of which possibly reduce fetal growth. Caffeine also increases cellular cyclic adenosine monophosphate, which may influence cell development.5
Pregnant women with a high caffeine intake (>300 mg a day) have been shown to give birth to babies with a birth weight 100-200 g lower than those of women with a low caffeine intake,678 although not all studies found this association.910 A high daily caffeine intake has also been associated with an increased risk of giving birth to small for gestational age or low birth weight (