For pregnant women, just half a cup of coffee a day may reduce neonatal birth size and body weight, according to a prospective study involving more than 2,500 women.
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That’s only 50 mg of a caffeine day, which falls below the upper threshold of 200 mg set by the American College of Obstetricians and Gynecologists, lead author Jessica Gleason, PhD, MPH, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Md, and colleagues reported.
“Systematic reviews and meta-analyses have reported that maternal caffeine consumption, even in doses lower than 200 mg, is associated with a higher risk for low birth weight, small for gestational age (SGA), and fetal growth restriction, suggesting there may be no safe amount of caffeine during pregnancy,” the investigators wrote in JAMA Network Open.
Findings to date have been inconsistent, with a 2014 meta-analysis reporting contrary or null results in four out of nine studies.
Dr. Gleason and colleagues suggested that such discrepancies may be caused by uncontrolled confounding factors in some of the studies, such as smoking, as well as the inadequacy of self-reporting, which fails to incorporate variations in caffeine content between beverages, or differences in rates of metabolism between individuals.
“To our knowledge, no studies have examined the association between caffeine intake and neonatal anthropometric measures beyond weight, length, and head circumference, and few have analyzed plasma concentrations of caffeine and its metabolites or genetic variations in the rate of metabolism associated with neonatal size,” the investigators wrote.
Dr. Gleason and colleagues set out to address this knowledge gap with a prospective cohort study, including 2,055 nonsmoking women with low risk of birth defects who presented at 12 centers between 2009 and 2013. Mean participant age was 28.3 years and mean body mass index was 23.6. Races and ethnicities were represented almost evenly even across four groups: Hispanic (28.2%), White (27.4%), Black (25.2%), and Asian/Pacific Islander (19.2%). Rate of caffeine metabolism was defined by the single-nucleotide variant rs762551 (CYP1A2*1F), according to which, slightly more women had slow metabolism (52.7%) than fast metabolism (47.3%).
Women were enrolled at 8-13 weeks’ gestational age, at which time they underwent interviews and blood draws, allowing for measurement of caffeine and paraxanthine plasma levels, as well as self-reported caffeine consumption during the preceding week.
Over the course of six visits, fetal growth was observed via ultrasound. Medical records were used to determine birth weights and neonatal anthropometric measures, including fat and skin fold mass, body length, and circumferences of the thigh, arm, abdomen, and head.
Neonatal measurements were compared with plasma levels of caffeine and paraxanthine, both continuously and as quartiles (Q1, ≤ 28.3 ng/mL; Q2, 28.4-157.1 ng/mL; Q3, 157.2-658.8 ng/mL; Q4, > 658.8 ng/mL). Comparisons were also made with self-reported caffeine intake.
Women who reported drinking 1-50 mg of caffeine per day had neonates with smaller subscapular skin folds (beta = –0.14 mm; 95% confidence interval, –0.27 to -–0.01 mm), while those who reported more than 50 mg per day had newborns with lower birth weight (beta = –66 g; 95% CI, –121 to –10 g), and smaller circumferences of mid-upper thigh (beta = –0.32 cm; 95% CI, –0.55 to –0.09 cm), anterior thigh skin fold (beta = –0.24 mm; 95% CI, –0.47 to -.01 mm), and mid-upper arm (beta = –0.17 cm; 95% CI, –0.31 to –0.02 cm).
Caffeine plasma concentrations supported these findings.
Compared with women who had caffeine plasma concentrations in the lowest quartile, those in the highest quartile gave birth to neonates with shorter length (beta = –0.44 cm; P = .04 for trend) and lower body weight (beta = –84.3 g; P = .04 for trend), as well as smaller mid-upper arm circumference (beta = -0.25 cm; P = .02 for trend), mid-upper thigh circumference (beta = –0.29 cm; P = .07 for trend), and head circumference (beta = –0.28 cm; P < .001 for trend). A comparison of lower and upper paraxanthine quartiles revealed the similar trends, as did analyses of continuous measures.
“Our results suggest that caffeine consumption during pregnancy, even at levels much lower than the recommended 200 mg per day of caffeine may be associated with decreased fetal growth,” the investigators concluded.
Dr. Sarah Prager
Sarah W. Prager, MD, of the University of Washington, Seattle, suggested that the findings “do not demonstrate that caffeine has a clinically meaningful negative clinical impact on newborn size and weight.”
She noted that there was no difference in the rate of SGA between plasma caffeine quartiles, and that most patients were thin, which may not accurately represent the U.S. population.
“Based on these new data, my take home message to patients would be that increasing amounts of caffeine can have a small but real impact on the size of their baby at birth, though it is unlikely to result in a diagnosis of SGA,” she said. “Pregnant patients may want to limit caffeine intake even more than the ACOG recommendation of 200 mg per day.”
Dr. Robert Silver
According to Robert M. Silver, MD, of the University of Utah Health Sciences Center, Salt Lake City, “data from this study are of high quality, owing to the prospective cohort design, large numbers, assessment of biomarkers, and sophisticated analyses.”
Still, he urged a cautious interpretation from a clinical perspective.
“It is important to not overreact to these data,” he said. “The decrease in fetal growth associated with caffeine is small and may prove to be clinically meaningless. Accordingly, clinical recommendations regarding caffeine intake during pregnancy should not be modified solely based on this study.”
Dr. Silver suggested that the findings deserve additional investigation.
“These observations warrant further research about the effects of caffeine exposure during pregnancy,” he said. “Ideally, studies should assess the effect of caffeine exposure on fetal growth in various pregnancy epochs as well as on neonatal and childhood growth.”
The study was funded by the Intramural Research Program of the NICHD. Dr. Gerlanc is an employee of The Prospective Group, which was contracted to provide statistical support.