Three-year study examines trans women’s breast development from feminizing HRT (2024)

For trans women and transfeminine people who are considering or at the very beginning of feminizing hormone therapy, one of the most common points of concern – and uncertainty – is breast development. How soon will it start, how fast will it happen, how long will it take, and how large will they become? “What will my breasts look like?” can be a question that many trans women have pondered for years before we ever take the step of bringing them into being.

It’s also a question that, for a given individual, can’t be reliably predicted or answered definitively ahead of time – the only way to find out is to go through with it and discover this firsthand. As with cis women, the dimensions of breast development can vary substantially among trans women on HRT. And while we may not be able to offer a specific answer for an individual, we can obtain information on the typical scope and range of that development among trans women as a group, and how that may differ from the ranges of development exhibited by cis women.

A recent study takes a useful step toward clarifying the typical course of breast growth seen in trans women and transfeminine people on HRT. de Blok et al. (2020) followed 69 trans women at Amsterdam’s VU University Medical Center gender clinic from the time they started taking feminizing HRT to three years later, taking several measurements of breast development at regular intervals. All trans women in the study started hormone therapy as adults, at a median age of 26 (with the middle 50% starting at ages 21 through 38). Notably, a 3D scanner was used with placement of markers at various key points on the breasts and chest area to obtain more accurate measurements, including calculation of breast volume, and an increase of 150 cc was considered to be an increase of one cup size.

What were the outcomes at the end of three years of HRT? In overall breast volume, a substantial majority (71%) had developed less than an A cup, but some trans women did experience greater growth – sometimes much greater:

After 36 months, most trans women (71%) had a breast volume corresponding to a bra cup size smaller than an A-cup. Only 9% had an A-cup (130 to 150 cc), 16% a B-cup (150 to 300 cc), 3% a C-cup (300 to 450 cc) and 1% an E-cup (600 to 750 cc).

Areola diameter was also seen to increase from an average of 24.1 mm (about the size of an American quarter dollar) to 28.6 mm. However, with a standard deviation of 12.8 mm, there was a wide distribution of areola sizes: 68% of trans women in the study ultimately developed areolas between 15.8 mm (slightly less than an American dime) and 41.4 mm (slightly more than an American silver eagle). Although some trans women (and cis women) have at times reported that one of their breasts appears to be slightly larger than the other, the authors did not find any difference between left and right breast sizes in the study sample.

Notably, breast development and growth was observed to continue throughout the entire three-year period of the study, with the authors pointing out that these changes may go on to progress beyond the “2-3 years” estimated by the Endocrine Society and WPATH to be the timeframe in which breast growth is completed. This would be compatible with anecdotal reports by trans women of breast growth continuing at 5 years of HRT and beyond.

Ultimately, this study was not able to identify any specific factors that were associated with greater or lesser breast size: “No associations were found between increase in breast volume and age, BMI, tobacco use, treatment regimen, and serum hormone levels.” At the end of the three-year followup period, 58% of trans women reported that they were satisfied with the size of their breasts.

This study has some important limitations:

• All trans women in the sample started HRT in adulthood without any prior treatment – they did not take puberty blockers in adolescence, and they experienced a masculinizing puberty which produces a broader chest and upper body. As a result, their breasts are positioned further apart on a larger chest, contributing to the appearance of smaller breasts; this factor was noted by Johns Hopkins researchers as a reason to choose the largest possible implants for trans women seeking breast augmentation. A sample of trans women who began transitioning with puberty blockers at Tanner stage 2 or 3, largely avoiding these masculinizing effects on their frame and body shape, might have had different outcomes in breast size, shape, and positioning, as well as satisfaction with breast development and appearance.
• Trans women in this sample used cyproterone acetate (CPA) as an antiandrogen, which is not in use or available in the United States. Unlike other antiandrogens such as spironolactone or GnRH agonists, CPA is a synthetic progestin and has progestogenic effects. If progestogens such as CPA, medroxyprogesterone acetate, and bioidentical progesterone have an effect on breast size and development – an open question with little evidence either way at present – a sample of trans women not using progestogens could report different outcomes than those found in this study.

Altogether, this study can help trans women and transfeminine people considering or starting HRT to develop informed expectations on what extent of breast development is likely for them, as well as what is potentially possible. These findings also suggest that the extent of growth is not something that trans women should regard as being within their control, whether through adjustments in hormone regimens or changes in body weight. Moreover, the clear trend toward smaller breast sizes, and particularly their aesthetics in the context of larger and broader chests typical seen among trans women who begin transitioning in adulthood, highlight the importance of access to breast augmentation surgery and its place as a medically necessary rather than cosmetic procedure for the treatment of gender dysphoria in a significant proportion of trans women. When satisfaction with breast size is little better than a coin flip with one form of treatment, other forms of treatment become all the more crucial. ■