Soru

A $28$-year-old female seeks evaluation alongside her partner due to primary infertility. The couple has been engaging in regular, unprotected vaginal intercourse for $14$ months without achieving conception. Her menarche occurred at age $12$. Her menstrual cycles are highly regular, occurring every $28$ days with $5$ days of moderate bleeding. She utilizes a home basal body temperature tracking method, which consistently demonstrates a biphasic monthly pattern. Five years ago, she was treated for a sexually transmitted pelvic infection with a single dose of intramuscular ceftriaxone and a $14$-day course of oral doxycycline. She takes a daily prenatal vitamin. Her body mass index is $23 \text{ kg/m}^2$. Vital signs are within normal limits. Physical examination reveals normal female hair distribution, absent galactorrhea, and no cutaneous manifestations of hyperandrogenism. Pelvic examination is unremarkable, with no cervical motion tenderness or adnexal masses.

Recent laboratory studies reveal:
Thyroid-stimulating hormone: $1.8 \mu\text{U/mL}$
Prolactin: $12 \text{ ng/mL}$
Day $21$ serum progesterone: $14 \text{ ng/mL}$

Her partner's semen analysis shows a volume of $3.2 \text{ mL}$, a sperm concentration of $55 \times 10^6/\text{mL}$, $65\%$ progressive motility, and $8\%$ normal morphology.

Based on the provided clinical data, what is the most appropriate next diagnostic step for this couple?