New guidelines developed to support the safe use of GLP-1 medicines before, during and after pregnancy are limited by gaps in the evidence, the researchers who developed them have said.

An international team, led by the University of Plymouth said a lack of evidence in many areas meant they had to provide some of the advice based expert knowledge and experience.

Women are disproportionately affected by obesity which can have detrimental effects on their reproductive health, including contributing to difficulty conceiving, the guidelines published in Obesity Reviews note.

Obesity is also associated with adverse perinatal outcomes but to date there have not been any comprehensive, evidence-based guidelines on whether weight loss drugs are a safe way of managing weight before and after pregnancy.

The guidelines development team identified more than 30 studies to draw on but they were mostly small and observational.

In all, more than half of the clinical questions the researchers wanted to address could not be answered.

They found no studies on the long-term impact on mother and baby of using the medications

And there was a lack of evidence on the effects of stopping GLP-1 therapy before getting pregnant on rebound weight gain, glycaemia and fertility, they said.

Weight loss drugs may help women with obesity or infertility reach BMI thresholds required for fertility treatment on the NHS and improve fertility-related outcomes, but more research is also needed here, they added.

Based on what is known so far, the guidelines reiterate current advice that weight loss drugs should not be deliberately continued throughout pregnancy.

They also recommend appropriate counselling on reliable contraception when using weight loss drugs, with non-oral contraception needed in the case of tirzepatide.

Last year, the Medicines and Healthcare products Regulatory Agency warned that with many women purchasing the drugs online, they may not be aware of the risks.

It issued guidance warning women taking weight-loss injections to ensure they are also using effective contraception.

Use during breastfeeding should be decided on an individual, case-by-case basis, with monitoring for mother and baby, the guidance states.

For women who had gestational diabetes, use postpartum appears to be effective for weight reduction and glycaemic control but the best time to start the drugs is also not known, the researchers said.

Lead author Dr Kate Maslin, associate professor in women’s health and nutrition from the University of Plymouth, said the guidance was the first step in bridging the gap in information for women and doctors on the issue.

‘One key recommendation was that incretin-based medication therapy should not be deliberately continued throughout pregnancy.

‘However, for those who may have used the injections without realising they were pregnant, the current data show no increased risk for congenital anomalies following exposure in early pregnancy – which we hope will be reassuring.’

Dr Maslin is leading a study to learn more about women’s use of the weight loss injections in relation to their fertility, including understanding where they found their information, and how it affected their decision making around use of the medication.

‘Weight loss medications are readily available through private providers, although less so through the NHS. We need to do more to ensure health professionals have the best available information to hand, and women and families are supported to make informed choices.

‘The main takeaway from this current study is that much more research needs to be done to understand how weight loss injections affect all aspects of reproductive health.’

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Guidelines on weight-loss drugs before and after pregnancy show stark gaps in evidence