A 26-year-old woman, para 0, comes to the office for follow-up of irregular menstrual periods. She has a period every 15-90 days that lasts 2-14 days and ranges from spotting to quarter-sized clots. The patient and her husband have been trying to conceive, but it has been difficult to time intercourse given her erratic menstrual cycles. She has been exercising and losing weight and now has a BMI of 32 kg/m². Gynecologic examination shows normal external genitalia, a small mobile uterus, and normal adnexa. Endometrial sampling reveals coiled glands filled with carbohydrate-rich mucus, edematous stroma, and tortuous spiral arteries. At which time point on the graph below was the endometrial sampling most likely obtained?

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11ec160b_3cbd_41eb_9249_37da67122a70_MD0001_00 The uterine endometrium is a highly specialized mucosa that undergoes histologic transformation during the menstrual cycle in preparation for zygote implantation. The upper layer of the endometrium (the stratum functionale) consists of lamina propria studded with tubular glands, spiral arteries, and dilated capillaries. Histologic examination of these components with an endometrial biopsy allows for endometrial dating and evaluation for pathological processes. A normal menstrual cycle lasts for 21-35 days (28+/-7 days). The proliferative phase is the first half of the menstrual cycle (days 1-14), beginning with the first day of menses and ending with ovulation. During this time, estrogen stimulates proliferation of the stratum functionale. Normal proliferative endometrium consists of nonbranching, nonbudding, uniform glands evenly distributed throughout a uniform stroma (Choices A and E). In the midproliferative phase (Choice B), the glands are tubular, narrow, and lined with pseudostratified, elongated, mitotically active epithelial cells. The stratum functionale contains compact, nonedematous stroma. The uterine glands have increased in length and girth but still remain relatively straight. No secretions are present in the glandular lumens. The endometrium thickens, but the coiled spiral arteries remain limited to the deeper layers. At the end of the proliferative phase, ovulation occurs. Endometrial biopsy at ovulation shows a late proliferative endometrium with coiled glands and occasional cytoplasmic vacuoles in the glandular epithelium (Choice C). The secretory phase is the second half of the menstrual cycle (days 15-28), which follows ovulation. During this time, progesterone secreted by the corpus luteum in the ovary promotes the development of secretory endometrium. The glands increase in size and become more coiled, and the cells lining the glands acquire large cytoplasmic vacuoles. Glycogen-rich mucus is released into the glandular lumens. The stroma becomes increasingly edematous, and the prominent spiral arteries extend to the endometrial surface. The endometrial biopsy taken in this patient is consistent with the mid-secretory phase. Educational objective: The secretory phase of the menstrual cycle occurs between ovulation and menses, from days 15-28 of the normal menstrual cycle. Progesterone released by the corpus luteum causes the uterine glands to coil and secrete glycogen-rich mucus in preparation for embryo implantation. The endometrial stroma becomes edematous and completely traversed by tortuous spiral arteries that extend from the deeper layers to the uterine lumen. __________ References: Endometrial biopsy in DUB. (http://www.ncbi.nlm.nih.gov/pubmed/8979202)

A 26-Year-Old Woman, Para 0, Comes to the Office for Follow-Up