The endometrium is thinnest during which days of the menstrual cycle?

The endometrium is thinnest during which days of the menstrual cycle?

• A. 1-5
• B. 6-9
• C. 10-14
• D. 15-28

Answer: (B)

Endometrial thickness is smallest when shedding occurs at the start of the cycle. During days 1–5, the lining is thinnest (roughly a couple of millimeters). After menses, estrogen drives regrowth in the proliferative phase, so the lining becomes thicker through days 6–14 and then more so after ovulation under progesterone in the secretory phase. Therefore, the thinnest period is days 1–5, not days 6–9.

Endometrial thickness is smallest when shedding occurs at the start of the cycle. During days 1–5, the lining is thinnest (roughly a couple of millimeters). After menses, estrogen drives regrowth in the proliferative phase, so the lining becomes thicker through days 6–14 and then more so after ovulation under progesterone in the secretory phase. Therefore, the thinnest period is days 1–5, not days 6–9.