A new clinical study from Newson Health has found that body mass index (BMI) may have a greater impact on unscheduled bleeding in menopausal women using hormone therapy than previously thought - challenging assumptions about the role of hormone dosage alone.

The research, which looked at a group of over 200 menopausal women using both standard and off-label doses of transdermal estradiol  and different progesterone doses (common form of body identical HRT), found that it was a person’s BMI rather than their dose of estradiol that was linked to increased womb lining thickness, a potential indicator of bleeding risk.  

The findings are particularly important given that up to 40% of menopausal women taking HRT experience unscheduled bleeding, which can be worrying and often leads to unnecessary tests and procedures.

Current guidelines often focus on adjusting hormone doses to manage bleeding, but this new evidence suggests that a woman’s body weight and how she absorbs hormones may play an even bigger role and should be taken into consideration when tailoring care and treatment plans.

Of the 235 women who were part of the study, 74% of participants had a normal womb lining thickness on ultrasound scans, compared to 20% had a thickened lining (not needing any treatment), while the remaining 6% had unclear results needing further investigations but also did not need further treatment.

However, women who were overweight were more likely to have a thicker womb lining. It is known that fat cells produce an inflammatory type of estrogen (estrone) and also other chemicals (cytokines) that can increase inflammation and affect the womb lining.

The research found there was no link between hormone doses and womb lining thickness – women taking lower doses of estradiol sometimes had thicker linings of their womb than those taking higher doses. Also, there was no difference in womb thickness with different doses of progesterone.

This is important as research in the past has not investigated higher doses of estradiol or different doses of progesterone in this way. Many older studies have used synthetic hormones, which are very different and associated with risks compared to body identical hormones which are safe.

Whilst HRT is a highly effective treatment for menopausal symptoms such as brain fog, joint pain and low mood as well as reducing the risk of future health issues including osteoporosis and cardiovascular disease, misinformation and fears around doses, side effects like unexpected bleeding often deter women from starting or continuing treatment.

Lead researcher Dr Louise Newson comments: ‘This research is pivotal – it reinforces the need for individualised care when it comes to hormone therapy, especially in women with higher BMIs, who may have unique treatment needs. More research needs to be done in this area, this is a small sample size but the results cannot be ignored.

Of course, if you are experiencing unscheduled bleeding while on hormone therapy, it’s important to consult your GP or healthcare provider.’

Mr Osama Naji, consultant gynaecologist at Guy’s and St Thomas’ NHS Foundation Trust who contributed to this study, states: ‘I am very delighted to see this important study providing reassuring evidence that the use of body identical menopausal hormone replacement therapy does not lead to concerning changes in endometrial thickness or increase the risk of significant consequences. It supports the safety of body identical hormone therapy in carefully selected women and adds to the growing body of data that can help patients feel more confident when considering such treatments.’

The study is published in Archives of Gynecology and Obstetrics and can be accessed here.

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