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Background There is no clear cutoff value for thyroid‐stimulating hormone (TSH) level that defines subclinical hypothyroidism (SCH). Moreover, TSH levels can be affected by numerous factors. Although mild SCH has been implicated in miscarriage, the relationship between TSH levels and miscarriage remains unelucidated. Methods We reviewed nine known risk factors affecting TSH levels and 28 studies investigating the potential association between mild SCH and miscarriage, examining whether these factors were considered. Main findings Among 28 studies that examined whether mild SCH (TSH > 2.5 mIU/L) contributed to miscarriage, thyroid antibodies were measured in only 15. TSH measurement methods were described in 18 studies. Although the iodinated contrast medium used in hysterosalpingography (HSG) is stored in the body for a long time and is a risk factor for mild SCH, only one study described its potential impact on TSH levels. Nine studies, which concluded that mild SCH contributed to miscarriage, had thyroid status evaluated only after the onset of pregnancy, but not before. Conclusion TSH levels can be significantly affected by patient demographics and health history, country of origin, and fertility treatment. It is important to consider these factors while evaluating mild SCH. It remains unclear how mild SCH contributes to miscarriage.

The sex of the conceived child is a significant concern for parents. To verify whether there women have pregnancy bias toward boys or girls, we investigated whether the history of continuous same-sex pregnancy was associated with the subsequent child’s sex. We prospectively analyzed data from the Japan Environment and Children’s Study, a birth cohort study. We included all cases of singleton live births (n = 98 412). Women with pregnancy due to infertility treatment were excluded (n = 6255); Similarly, women with a history of miscarriage, artificial abortion, stillbirth, and multiple pregnancies, and those with missing data on the sex of the previous child were excluded. Altogether, 62 718 women were included. For the first live birth, a male-biased sex ratio of 1.055 was observed. Further, no significant difference was found in the sex ratio of the conceived child between women with one boy and those with one girl previously. However, when there were more than two children previously, the subsequently conceived child’s male/female sex ratio was significantly higher among boy-only mothers than among girl-only mothers. The results indicated that several pregnant women are biased toward conceiving either boys or girls.

Purpose We investigated the contribution of subchorionic hematoma (SCH) involvement in early pregnancy to the risk of pregnancy complications in women who underwent frozen‐thawed embryo transfer (FET). Methods A hypoechogenic area surrounding the gestational sac at early pregnancy on ultrasound was defined as SCH. Simultaneously, the presence of vaginal bleeding was evaluated. We included 1416 women with live births after FET between March 2015 and September 2018 in this study. The frequency of pregnancy complications was compared between the SCH (n = 340) and non‐SCH (n = 1076) groups. Results The adjusted odds ratio of abnormal placental adhesion and placenta previa for the SCH group relative to the non‐SCH group was 7.01 [2.96‐18.00] and 3.77 [1.24‐11.91], respectively. In contrast, hypertensive disorders of pregnancy, non‐reassuring fetal status, fetal growth restriction, chorioamnionitis, and premature rupture of the membrane showed no differences between both groups. Furthermore, the frequency of abnormal placental adhesion was higher in the SCH group with vaginal bleeding than in the SCH group without vaginal bleeding. Conclusions Subchorionic hematoma in early pregnancy may cause abnormal placental adhesion and placenta previa in pregnant women with FET. SCH presence should be carefully noted, particularly in cases with vaginal bleeding during early pregnancy after FET. Subchorionic hematoma in early pregnancy may cause abnormal placental adhesion and placenta previa in pregnant women with frozen embryo transfer. SCH presence should be carefully noted, particularly in cases with vaginal bleeding during early pregnancy after frozen embryo transfer.

Purpose To study the effects of mildly elevated thyroid‐stimulating hormone (TSH) levels and thyroid antibodies on pregnancy rates among infertile women and their potential contribution to prolonged infertility treatment. Methods This case‐control study included 1479 women who underwent infertility treatment between March 2015 and August 2017. Cumulative pregnancy and miscarriage rates after assisted reproductive technology (ART) or non‐ART treatments were compared between women with TSH <2.5 mIU/L and those with TSH 2.5‐3.5 mIU/L and between women with and without thyroid antibody positivity. Results The cumulative pregnancy rate of women with TSH 2.5‐3.5 mIU/L was similar to that of women with TSH <2.5 mIU/L in the non‐ART (hazard ratio [HR], 0.85; 95% confidence interval [CI], 0.56‐1.23) and ART (HR, 1.17; 95% CI, 0.93‐1.47) groups. Thyroglobulin antibody (TgAb) and thyroid peroxidase antibody (TPOAb) had no correlation with cumulative pregnancy rates. In the non‐ART and ART groups, HRs for TgAb were 0.87 (95% CI, 0.55‐1.32) and 1.09 (95% CI, 0.84‐1.39) and HRs for TPOAb were 0.88 (95% CI, 0.52‐1.39) and 1.29 (95% CI, 0.97‐1.68), respectively. Conclusions Cumulative pregnancy rates and miscarriage rates were similar between women with TSH <2.5 mIU/L and those with TSH 2.5‐3.5 mIU/L and were independent of thyroid antibody positivity.

Purpose We investigated the clinical results of Japanese men with Y chromosome microdeletions. Methods This study retrospectively examined 2163 azoospermic or severe oligozoospermic patients. We investigated the frequency of azoospermia factor (AZF) deletions and sperm retrieval rate (SRR) by microTESE in patients with these deletions, then analyzed the ICSI outcomes. Results Azoospermia factor deletions were found in 201 patients. SRR was significantly higher than that of the control group (74.0% vs 20.4%, P < .001). Thirty‐three couples underwent ICSI using testicular spermatozoa retrieved by microTESE, and eight couples underwent ICSI using ejaculatory spermatozoa. The fertilization rate and clinical pregnancy rate per embryo transfer cycle were significantly higher in the ejaculatory group than that of the testicular group (66.4% vs 43.7%, P < .001, 53.3% vs 24.7%, P = .03, respectively). When compared with the control group, the fertilization rate was significantly lower in the testicular group with AZFc microdeletions (43.7% vs 53.6%, P < .001). Conclusions Our study highlights that although microTESE in azoospermic men with AZFc microdeletions led to a higher SRR, ICSI outcomes of these men were worse than that of men without AZF deletions, even if testicular spermatozoa were retrieved.

Purpose Our aim is to make an ideal embryo culture medium close to human oviduct fluid (HOF) components, and to evaluate the quality of this medium with embryo quality and clinical outcomes in assisted reproductive technology (ART) by a prospective randomized controlled trial (RCT). Methods Study I: HOF was collected laparoscopically from patients (n = 28) with normal pelvic findings. According to HOF analysis results, the new medium “HiGROW OVIT®” (OVIT) was designed. Study II: Embryos (2 pronuclei (2PN) = 9633) were assigned from 1435 patients. The blastulation rate (BR), good BR (gBR), utilized (transferred/cryo‐preserved) BR (uBR), pregnancy rate (PR), and miscarriage rate (MR) were compared between the OVIT and control groups by RCT. Results The novel medium ‘OVIT’ was produced according to 31 HOF components. The concentrations of essential amino acids (e‐AAs) were lower in OVIT than in current media, yet the opposite was true for ne‐AA concentrations. gBR and uBR were higher in the OVIT group than in the control group. In the older female group, gBT and uBR were significantly higher in the OVIT group. Conclusions The novel medium ‘OVIT’ was produced according to HOF data. The OVIT had significantly better embryo quality and clinical outcomes than the current media.

Purpose Cervical mucus plays an important role in host defense mechanisms and is involved in the ascendance of sperm. To determine the change of neutrophil mediators contained in cervical mucus, we measured total neutrophil elastase (NE) levels throughout the menstrual cycle. Methods Cervical NE concentrations in 31 healthy women having regular ovulatory cycles were measured during the follicular, ovulatory and luteal phases. Results The cervical NE levels during the follicular, ovulatory and luteal phases were 0.73 ± 0.57 (mean ± SD), 0.29 ± 0.33 and 1.32 ± 1.24 μg/ml, respectively. The NE concentrations during the ovulatory phase were significantly lower than the other phases. Conclusions The decrease in total cervical NE level during the ovulatory phase suggests that neutrophil activity in cervical mucus is depressed around ovulation. The decreased cervical NE levels and the depressed neutrophil activity in cervical mucus at ovulation may be suitable for sperm passage through the cervical canal.

To study whether subchorionic hematoma (SCH) location and size in early pregnancy affect placenta accreta spectrum (PAS) risk in hormone replacement cycles (HRC). Retrospective cohort study of 685 singleton live births following frozen-thawed embryo transfer in HRC (November 2018-September 2023) at a single fertility clinic. SCH location (cervical-side, mid-cavity, or fundal-side) and size (< 10% or > 50% of gestational sac), assessed by first-trimester ultrasound, were evaluated for association with PAS. The presence of SCH showed a trend toward increased PAS frequency (adjusted Risk Ratio (RR) 1.56, 95% Confidence Interval (CI) 0.87-2.80). Location-specific analysis revealed that cervical-side SCH conferred significantly elevated PAS risk compared to those without cervical-side SCH (adjusted RR 2.21, 95% CI 1.18-4.15), whereas mid-cavity SCH (adjusted RR 1.74, 95% CI 0.94-3.22) and fundal-side SCH (adjusted RR 0.59, 95% CI 0.20-1.76) showed no significant association. Regarding SCH size, larger hematomas (> 50% of gestational sac) were not associated with increased PAS risk compared to smaller hematomas (< 10%) (adjusted RR 0.59, 95% CI 0.16-2.13). Cervical-side SCH, but not mid-cavity or fundal-side hematomas, was associated with increased PAS risk in HRC pregnancies. These findings suggest that SCH location may serve as a key prognostic marker in HRC.