The gonadotropin-releasing hormone (GnRH) neurons exhibit pulse and surge modes of activity to control fertility. They also exhibit an unusual bipolar morphology comprised of a classical soma-proximal dendritic zone and an elongated secretory process that can operate as both a dendrite and an axon, termed a ‘dendron’. We show using expansion microscopy that the highest density of synaptic inputs to a GnRH neuron exists at its distal dendron. In vivo, selective chemogenetic inhibition of the GnRH neuron distal dendron abolishes the luteinizing hormone (LH) surge and markedly dampens LH pulses. In contrast, inhibitory chemogenetic and optogenetic strategies targeting the GnRH neuron soma-proximal dendritic zone abolish the LH surge but have no effect upon LH pulsatility. These observations indicate that electrical activity at the soma-proximal dendrites of the GnRH neuron is only essential for the LH surge while the distal dendron represents an autonomous zone where synaptic integration drives pulsatile GnRH secretion.

The use of progestin (P) during ovarian stimulation is effective in blocking the luteinizing hormone (LH) surge in women with normal ovarian reserve, however, its effects have not been determined in poor responders. This study aimed to explore the follicular dynamics in P-primed minimal stimulation in poor responders. A total of 204 infertile women with diminished ovarian reserve were allocated into the medroxyprogesterone acetate (MPA) group or the natural-cycle control group in an alternating order. MPA (10 mg) was administered daily beginning from the early follicular phase and a low dose of hMG was added in the late follicular phase if the serum FSH level was lower than 8.0mIU/ml. When a dominant follicle reached maturity, triptorelin 100 μg and hCG 1000 IU were used for trigger, and oocytes were retrieved 34-36 h later.All viable embryos were cryopreserved for subsequent frozen embryo transfer. Natural cycle IVF was used as controls. Compared with the natural cycle group, the MPA group exhibited a larger pre-ovulatory follicle (18.7 ± 1.8 mm vs 17.2 ± 2.2 mm), a longer follicular phase (13.6 ± 3.6 days vs 12.3 ± 3.2 days), and higher peak oestradiol values (403.88 ± 167.16 vs 265.26 ± 122.16 pg/ml), while maintaining lower LH values (P < 0.05). The incidences of spontaneous LH surge and premature ovulation decreased significantly (1.0% vs 50%; 2% vs. 10.8%, respectively; P < 0.05). A greater number of oocytes and viable embryos were harvested from the MPA group than from the natural cycle group (P < 0.05). Moreover,the clinical pregnancy rate was slightly higher in the MPA group than in the natural cycle controls, but the difference was not significant (11.8% vs 5.9%, P > 0.05). This study supported the hypothesis that P-primed minimal stimulation achieved ovulation control of the dominant follicle and did not adversely affect the quality of oocytes in poor responders. Therefore, P-priming is a promising approach to overcome premature ovulation in minimal stimulation for poor responders. ChiCTR-OCH-14004176 . Registered on January 8, 2014.

Is transferring embryos that achieve blastulation on Day 7 effective and safe? Embryos that achieve blastulation on Day 7 resulted in clinically relevant rates of clinical pregnancy (32.5%) and live birth (25.2%), and newborns have a similar risk of low birth weight, congenital malformations or early neonatal death compared with those derived from Days 5 and 6 blastocysts. Potential advantages of blastocyst transfer over cleavage embryo transfer have led to a shift toward the former in IVF practice. However, published data about the fertility outcomes of transferring embryos with a delayed blastulation on Day 7 are scarce and controversial. Moreover, there are few data available on the neonatal outcomes of Day 7 blastocysts. As a result, the clinical value of Day 7 blastocysts is uncertain. This was a retrospective cohort study that included 2908 women undergoing frozen–thawed embryo transfer cycles of IVF/ICSI from January 2006 to May 2015, and reported on the 1518 live born infants from those cycles. We used propensity score matching to compare the fertility outcomes of women undergoing Day-5, Day-6 and Day-7 vitrified embryo transfers in three matched comparisons (Day 5 vs Day 6, Day 5 vs Day 7 and Day 6 vs Day 7). We also compared neonatal outcomes among babies derived from Day-5, Day-6 and Day-7 vitrified embryo transfers. We studied 922 Day-5, 1752 Day-6 and 234 Day-7 vitrified embryo transfers. Day-7 vitrified embryo transfers had significantly lower implantation, clinical pregnancy and live birth rates than both Day-5 (23.9 vs 49.9%, 31.7 vs 58.1% and 25.1 vs 46.5%, all P < 0.001, respectively) and Day-6 (24.7 vs 42.3%, 33.0 vs 53.2% and 25.6 vs 41.4%, all P < 0.001, respectively) vitrified embryo transfers. Assessment of babies showed no statistically significant difference in the rates of low birth weight, congenital malformations and early neonatal death among the 585, 869 and 64 babies born from Day-5, Day-6 and Day-7 vitrified embryo transfer groups, respectively. This was a single center retrospective study, and most of the neonatal data were extracted from parental questionnaires. Besides, the number of Day-7 vitrified embryo transfer cycles and babies born from these cycles was still limited, thus reducing the power of our study in assessing neonatal outcomes. In addition, only the morphologically poorer Day 3 embryos were extendedly cultured, and poorer blastocysts were qualified for vitrification on Day 7 than on Day 5 or 6, both of which might bias clinical pregnancy rates. Transfer of embryos that reach the blastocyst stage on Day 7 results in lower but still acceptable live birth rate, and seems to be safe for the offspring. Extension of the culture time in embryos that do not reach blastocyst stage by Day 6 should be assessed in randomized clinical trials. This work was supported by the National Nature Science Foundation of China (Grant nos. 81771533, 81571397, 81571486, 31770989 and 81501319), the Nature Science Foundation of Shanghai (Grant nos. 15ZR1424900 and 1441196300), and the Foundation of Health and Family Planning Commission of Shanghai (Grant no. 201540237). B.W.M is supported by the National Health and Medical Research Council (NHMRC) Practitioner Fellowship (GNT1082548), B.W.M reports consultancy for ObsEva, Merck and Guerbet. Not applicable.

As an effective inhibitor of premature ovulation, progestin was introduced to a novel ovarian stimulation regimen for infertility treatment. However, the local action of progestin on the ovary and its effect on clinical outcomes have not been described. The influence of progesterone administration on clinical oocyte outcomes and the mechanisms involved in the coordination of progesterone and follicle stimulating hormone (FSH) on follicle growth and oocyte yields were investigated. Clinical outcomes of patients undergoing ovarian stimulation for in vitro fertilization were analyzed. The murine ovarian stimulation model and follicle culture system were used to evaluate the effects of progesterone on oocyte yield, follicle development, granular cell proliferation, and hormone secretion. Phospho-specific protein microarrays were used to explore involved signaling pathways. Progesterone decreased clinical oocyte yields, and yields were rescued with an increased dose of human menopausal gonadotropin. Administration of progesterone inhibited murine granular cell proliferation and reduced the growth rate of follicles; both of which were rescued by FSH. The phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT) and mitogen-activated protein kinase (MAPK) were identified as pivotal signaling pathways to integrate progesterone into the FSH signaling network in granular cells. Progesterone inhibited granular cell proliferation and antral follicle growth during ovarian stimulation, and subsequently influenced oocyte outcomes in the clinical setting. Progesterone coordinated with FSH to regulate follicle growth through PI3K/AKT and MAPK signaling pathways. These findings advance our knowledge regarding the ovarian response to gonadotropins during progestin-primed ovarian stimulation and create an opportunity to manipulate individual oocyte yields.

Increased risk of monozygotic twinning (MZT) has been shown to be associated with assisted reproduction techniques, particularly blastocyst culture. Interestingly, inner cell mass (ICM) splitting in human ‘8’-shaped hatching blastocysts that resulted in MZT was reported. However, the underlying cause of MZT is not known. In this study, we investigated in a mouse model whether in vitro culture leads to ICM splitting and its association with hatching types. Blastocyst hatching was observed in: (i) in vivo developed blastocysts and (ii–iii) in vitro cultured blastocysts following in vivo or in vitro fertilization. We found that ‘8’-shaped hatching occurred with significantly higher frequency in the two groups of in vitro cultured blastocysts than in the group of in vivo developed blastocysts (24.4% and 20.4% versus 0.8%, respectively; n = 805, P < 0.01). Moreover, Oct4 immunofluorescence staining was performed to identify the ICM in the hatching and hatched blastocysts. Scattered and split distribution of ICM cells was observed around the small zona opening of ‘8’-shaped hatching blastocysts. This occurred at a high frequency in the in vitro cultured groups. Furthermore, we found more double OCT4-positive masses, suggestive of increased ICM splitting in ‘8’-shaped hatching and hatched blastocysts than in ‘U’-shaped hatching and hatched blastocysts (12.5% versus 1.9%, respectively; n = 838, P < 0.01). Therefore, our results demonstrate that extended in vitro culture can cause high frequencies of ‘8’-shaped hatching, and ‘8’-shaped hatching that may disturb ICM herniation leading to increased risk of ICM splitting in mouse blastocysts. These results may provide insights into the increased risk of human MZT after in vitro fertilization and blastocyst transfer.