Ambassador and OB/GYN Marta Perez weighs in on what she thinks about a new study that suggests caffeine is harmful during pregnancy.
Recently, you may have a news headline about a new study suggesting that even small amounts of caffeine in pregnancy were harmful. This is a departure from current guidelines from reputable organizations, which state that 200mg-300mg of caffeine per day is safe in pregnancy.
So what does this new study mean for our pregnant patients?
It’s important to know *what* the new study is to understand what it *means.* It’s important to understand that not all studies are created equal. Research can be high or low quality depending on its methodology, sample size, and ability to control for confounders and bias. This new study in the British Medical Journal (link below) is a meta-analysis, a collection of older observational data and a few meta-analyses of observational data. Observational data is lower quality than prospectively collected randomized data because of higher confounders and bias. In the absence of better quality data, combining results of different observational size can increase sample size and statistical tools can be used to analyze the new grouped population. This study did not use statistical techniques to increase sample sizes, it just collected studies to report their findings.
This study included 42 studies, 32 of which had reported an association between (higher) caffeine use and a negative pregnancy outcome, while 10 found no relationship. Included studies used different amounts of caffeine consumption when they were performed, some at 150mg, some at 300mg, some at “cups of coffee” rather than using caffeine amount at all. Because of the varying amounts of use in different studies including under the current recommended guidelines, this study concludes that there is no safe level for use, but rather a dose-response relationship, with increasing caffeine use contributing to increasing risks. The negative pregnancy outcomes used were miscarriage, stillbirth, preterm birth, low birth weight or small for gestational age, childhood leukemia, and childhood overweight/obesity.
What is my opinion as an OB-GYN?
I think that this study has many limitations - it does not add new data, include the magnitude of increased risk for outcomes, most studies did include caffeine consumption cutoffs (instead of no use at all) but the cutoffs were all different amounts, and the inherent lesser quality of observational data. I do think studies like this that challenge our existing recommendations are valuable because they provide an opportunity to cast doubt on an existing recommendation which means the scientific community can justify the need for a large, randomized control trial that would be of much higher quality.
In my opinion, a big confounder here could be the “why” of caffeine consumption, things like nocturnal/shift work, emotional & physical stressors which lead to poor sleep quality and exhaustion; which may be the underlying cause of negative outcomes and not the caffeine use itself. A large, randomized prospective trial could control for some of these variables and give us a clearer picture of the true impact of caffeine on pregnancy outcomes.
Based on this study alone, I would not necessarily advocate for changes to existing recommendations that 200-300mg of caffeine in pregnancy is acceptable, but I will use more nuance in the discussion, recognizing new challenges to this guideline. It’s possible in the future we will have a study that is high quality that will give us more clarity in recommendations around caffeine use and pregnancy and I look forward to that!
Dr. Marta Perez is a board certified OB-GYN and has a passion for sharing reliable reproductive health information online via her Instagram (@dr.martaperez), where you can find her busting myths, sharing knowledge, and empowering lives. Also on her YouTube channel are videos specifically focused on birth and understanding the process and complications.