The patient was a 36-year-old G0P0 woman who presented to our fertility center seeking fertility treatment. The body mass index of the patient was 16.4 kg/m2 (body weight, 38.2 kg). The patient had no prior surgical history, known allergies, or medications, including prenatal vitamins. The patient denied any history of sexually transmitted infections and had normal hysterosalpingogram and saline sonohysterograms. The levels of anti-Müllerian hormone was 8.56 ng/mL, and on day 3 of the menstrual cycle estradiol (E2), follicle-stimulating hormone, and luteinizing hormone were 55.0 pg/mL, 6.6 mU/mL, and 10.9 mU/mL, respectively. The partner of the patient was diagnosed with male factor infertility. Therefore, the patient was scheduled for in vitro fertilization (IVF). The first IVF cycle used a fixed gonadotropin-releasing hormone (GnRH) antagonist stimulation protocol. Clomiphene citrate (50 mg/day for 5 days) and recombinant human follicle-stimulating hormone (Gonal-F®, Merck Serono, Tokyo, Japan) at 150 IU every alternative day and on day three of the menstrual cycle, respectively were used for stimulation. On days 10 and 11 of the menstrual cycle, human menopausal gonadotropin (225 IU, Ferring Pharma, Tokyo, Japan) with a GnRH antagonist, cetrorelix acetate (0.25 mg, Cetrotide; Merck Serono, Tokyo, Japan), was administered. Final follicular maturation was induced with a nasal spray of GnRH agonist (600 µg, Buserecure, Fuji Pharma, Tokyo, Japan). On the day of the trigger, the concentrations of E2, progesterone, and luteinizing hormone were 4,328 pg/mL, 0.9 ng/mL, and 11.8 mIU/mL, respectively. Oocyte retrieval was performed 35 h after the trigger under general anesthesia. A total of 14 cumulus-oocyte complexes were retrieved, and 14 oocytes reached the MII stage. Because of the high E2 concentration on the day of trigger, the dopamine agonist cabergoline (0.5 mg) was also administered daily after oocyte retrieval to prevent ovarian hyperstimulation syndrome. Conventional IVF and intracytoplasmic sperm injection were performed according to semen parameters. Blastocysts were evaluated according to Gardner’s classification . Three blastocysts (4BB, 4BC, and 6BC) were obtained and cryopreserved by vitrification using a Cryotop carrier system (Kitazato Biopharma Co., Tokyo, Japan) according to the manufacturer’s instructions. Afterward, vitrified-warmed ET was scheduled, and endometrial preparation was performed using a hormone replacement cycle (HRC). In the HRC, transdermal estradiol (0.72 mg, ESTRANA TAPE, Hisamitsu Pharmaceutical, Tokyo, Japan) was administered from cycle day 3. Progesterone treatment with vaginal progestin tablets (300 mg/day, LUTINUS Vaginal Tablet, Ferring Pharmaceuticals Co., Ltd., Tokyo, Japan) and oral dydrogesterone tablets (30 mg/day, Duphaston, Mylan EPD, Tokyo, Japan) was administered at an endometrial thickness of 8 mm. Vitrified-warmed ET was performed five days after the start of progesterone treatment. Progesterone treatment was continued for 10 weeks after confirming positive serum β-human chorionic gonadotropin (β-hCG).
After the first frozen single ET (FET) of 4BB blastocyst following the HRC protocol described above (Fig. 1A), intrauterine fetal death was diagnosed at 19 weeks of gestation, and the patient eventually had a stillbirth. The baby and the placenta showed no obvious congenital abnormalities. The patient refused further examinations for stillbirth, such as placental pathological examination and genetic analysis. Thereafter, the patient experienced two spontaneous abortions at 9 and 4 weeks of gestation after each FET of 6BC (Fig. 1B) or 4BC (Fig. 1C) blastocysts following the HRC protocol described above. Therefore, she underwent a standard RM workup, including an investigation of the coagulation factors such as protein C, protein S, antithrombin III, LA, and aCL- IgG and aCL-IgM to rule out possible potential prothrombotic causes. Hysteroscopy was performed on the patient, and karyotypes of the patient and her partner were analyzed. The results showed that only aCL-IgG was positive and elevated to 22.0 U/mL, whereas other parameters were unremarkable. Hysteroscopy did not reveal any remarkable findings, and karyotypes were normal. According to the classification criteria for definite APS , aCL-IgGs were re-examined 12 weeks later to determine whether they were continuously positive, which revealed negative results suggesting an occasional aPL-positivity. Therefore, it was inferred that the unexplained RM in the patient could be due to occasional aPL-positivity but not APS. We discussed the next strategy with the patient to avoid miscarriage and succeed in pregnancy. Accordingly, ET using a single embryo and simultaneous treatment with LDA, LMWH, or combined therapy of LMWH and LDA was planned based on the results obtained in previous studies .
Using the same protocol for HRC, as described above, the vitrified-warmed blastocyst graded 4AB (Fig. 1D) was transferred, and only LDA (enteric-coated aspirin tablet, 100 mg once daily) (Bayaspirin; Bayer Pharmaceutical Co., Ltd., Tokyo, Japan) was administered starting on the day of ET and continued until a successful clinical pregnancy was determined using ultrasound. Although the serum hCG concentration was elevated to 9.9 IU/L two weeks after the ET, a clinical pregnancy with the gestational sac in the uterus was not confirmed afterward. On the next ET cycle, the vitrified-warmed blastocyst graded 4AB was transferred (Fig. 1E), and the combined intervention of LMWH (10,000 IU every 12 h; Mochida Pharmaceutical Co., Ltd., Tokyo, Japan) and LDA (enteric-coated aspirin tablet, 100 mg once daily) was performed on the day of ET using the same protocol of HRC and luteal support and continued for 14 and 28 weeks of gestation, respectively (Fig. 2). Sixteen days post-ET, serum HCG concentration was elevated to 2562.0 IU/L, confirming a pregnancy. A transvaginal ultrasound was performed 3–4 weeks later to confirm a clinical pregnancy with a viable fetal heartbeat. A repeat ultrasound scan performed at 12 weeks of gestation ensured the viability of the fetus. The patient successfully completed the course of pregnancy, went into spontaneous labor at 40 weeks of gestation, and gave birth to a viable female neonate (3010 g) at 40 weeks and 3 days of gestation. The neonate had an Apgar score of 8/9 out of 10. The postpartum course was stable, and the patient was discharged five days after delivery (Fig. 2).