I found this info while searching for causes of voice changes. Apparently one of the causes of voice changes is hormonal levels (whether through menstruation or otherwise). Not sure if it applies to us, trans people who are on hrt !?

http://www.uiowa.edu/voice-academy/male-female-voices


A woman's hormonal ups and downs may affect her mood, weight, energy level — and yes — her voice.

Some women's voices fluctuate just as their monthly hormones predictably ebb and flow. Usually, these changes show up in the voice right before menstruation occurs, although some women note changes during ovulation. Voice changes — due to falling estrogen levels — usually occur on day 21 or so:

loss of (singing) high notes;
vocal instability or fatigue;
pitch uncertainty;
decreased vocal efficiency;
huskiness;
reduced vocal power or flexibility.
Hormone shifts cause changes inside the larynx. Tissues hold fluid and blood vessels dilate, increasing vocal fold bulk. Puffier vocal folds vibrate differently, making speaking and singing more effortful. Interestingly, due to these effects, European opera houses used to excuse singers from singing during premenstrual and early menstrual days.

Pregnancy: Imagine the wild hormonal ride your vocal system endures in pregnancy. When a woman is expecting, estrogen and progesterone levels surge, causing swelling of vocal fold tissue, which are heavier and more sluggish to vibrate.

Expectant and lactating mothers may notice:

breathiness
hoarseness
prolonged warm-up time
a muffled voice quality
vocal fatigue
increased vocal effort.

Premenstruative hormone levels are by some described as being "Estrogen dominant", with Progesterone falling more rapidly than estrogens. This is also what might cause mood swings and other PMS symptoms. Estrogen dominance also increases water retention, causing slight formation of puffiness. So you may notice water retention in the breasts (tension sensation) or in the face (especially the chin and jawline area may become more puffy). The same is true for trans women who only receive estrogen and no progesteron, although some patients and doctors perceive these symptoms as positive (breast pain is interpreted as growth and a more puffy skin at the jawline may hide masculine features by softening the features a bit). But in the long run these are not really the changes one wants.
I personally believe this also affects the vocal chords. estrogen domonance (or vice versa lack of progesterone) might cause the vocal chords to retain more water and thus become a bit more massive. A total lack of testosterone and/or progesterone may cause muscles to be weakened, which includes the muscles that close the vocal folds. Hence most women have a "posterior gap" in their vocal folds when making a sound. The muscles at the back of the throat just are not as strong as in men and thus do not close that gap completely. My SLT said that this is the case in most women (and I can imagine it depends on the hormone cycle). She also said that this probably also contributes actually to a more "feminine" voice by making the voice more breathy and softer - at the expense of loudness and clarity though.

Spiro by the way acts similarly as progesterone in that it lowers the water retention in the tissue and thus some people have reported an elevated voice when taking Spiro.

Quote from: anjaq on April 05, 2016, 04:15:16 AM
Premenstruative hormone levels are by some described as being "Estrogen dominant", with Progesterone falling more rapidly than estrogens. This is also what might cause mood swings and other PMS symptoms.

I get the impression based on the studies I read that falling estrogen levels are more responsible for PMS symptoms than falling progesterone levels because when we give progesterone to these women, rarely symptoms improve  (they might even get worse) whereas when estrogen is given, symptoms tend to improve more.