Beyond body mass index: a synthesis of lifestyle factors that may influence in vitro fertilisation outcomes
There are several lifestyle factors that are thought to potentially impact in vitro fertilisation outcomes, including body mass index, smoking, alcohol consumption, caffeine, dietary patterns and physical activity. Eligibility criteria for in vitro fertilisation in England often require individuals to be non-smokers, drug free and have a body mass index <30kg/m2. Some researchers have questioned the scientific and ethical basis for the use of body mass index thresholds in fertility treatment, citing evidence that other factors may have a greater effect on the chance of success of in vitro fertilisation. This article aims to briefly synthesise the current evidence on how other factors such as smoking, alcohol, recreational drugs, smoking, caffeine, dietary patterns and physical activity may impact in vitro fertilisation outcomes.
Body mass index is used globally to determine access to fertility treatment, including in vitro fertilisation, with different countries imposing diverse limits (De Wert et al, 2014; Tremellen and Savulescu, 2016; Koning et al, 2017). Guidance in the UK imposes an in vitro fertilisation body mass index threshold of 30 kg/m2, with those with obesity advised to lose weight in order to restore ovulation, increase their response to ovulation induction agents and improve pregnancy outcomes (Emokpae and Brown, 2021; NHS, 2022a, b; 2023). A systematic review suggested that women with a body mass index >30 kg/m2 (classified as obese) have a clinical and statistically significant decreased probability of live birth following in vitro fertilisation, compared with women of healthy weight (body mass index: 18.5—24.9 kg/m2) (Sermondade et al, 2019). However, some researchers have questioned the scientific and ethical basis for the use of body mass index thresholds in fertility treatment (Koning et al, 2017; Tremellen et al, 2017), citing evidence that other factors may have a greater effect on the chance of success (Sneed et al, 2008; Koning et al, 2017).
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