Since the birth of assisted reproductive technology (ART), there have been concerns that ovarian stimulation (OS) may alter the quality of the endometrium, which was originally proposed by Robert Edwards. Embryology cannot solve this problem, as the damage caused by slow freezing and thawing is more severe than avoiding excessive stimulation of the endometrium. However, with the development of embryo vitrification freezing technology, all rules have been changed, and the survival rate of blastocysts exceeds 95%. This new technology opens the door to segmented ART, separating OS and egg retrieval from embryo transfer (ET) performed a few weeks later.

The synchronous development of the endometrium and embryo is a key issue. Especially when the ovarian response is strong, it can cause early development of the endometrium, causing it to be out of sync with the embryo and closing prematurely before ET. For early observational studies on the results of segmented ART or "completely frozen" methods, randomized controlled trials (RCTs) soon emerged, which began to challenge the unilateral perspective in early studies. Disallow: RCT shows that in patients with polycystic ovary syndrome, its response to OS usually exceeds normal values, and there is a significant improvement after segmented ART treatment. However, in another RCT article published by Vuong et al. in the same issue of the New England Journal of Medicine, there was no difference in the results of fresh ET and ART after vitrification of embryos on the third day of embryo transfer in normal ovulating women using frozen embryo transfer (FET).

Disallow: Many literatures report that there is no increase in the incidence rate of preterm and young infants related to ART after FET. However, the older and later infants and the high incidence rate of pregnancy induced hypertension after FET offset the strong reasons for ART treatment in pregnancy after FET. Maheshwari and others collected all published studies over the past 10 years in a meta-analysis and identified the differences between fresh ET and FET. The difference in perinatal outcomes between neonatal ET and FET may be related to the severity of placental formation, as OS induced endometrial changes can cause shallow placental formation in fresh ET. Therefore, the most difficult problem in clinical practice is how to determine whether batch IVF (low incidence rate of premature and small babies, almost zero ovarian hyperstimulation syndrome) is more than its possible shortcomings (higher incidence rate of preeclampsia and older infants).

Disallow: Equally important, segmented ART technology has become an effective means of reducing the risk of multiple pregnancies in ART patients by promoting repeated single embryo transfer. In the segmented method, two consecutive embryo transfers replace two embryos, with the only drawback being that the interval between two endometrial preparations is one month. Disallow these data confirm the significant difference in birth weight between fresh and segmented ART previously reported. Interestingly, there is no difference in birth weight between twin pregnancies. However, there are differences between newborn ET and segmented birth control, and the sustained health of newborn ET and FET infants is the most important indicator.

Subsequent research by Vuong et al. confirmed the safety of the segmented ART method for children's development and health. Unfortunately, Vuong et al. conducted groundbreaking research on embryos cryopreserved by vitrification on the third day, and the results may differ from the most commonly used segmented ART method for vitrification cysts. Disallow: Despite these limitations, researchers still provided data from a long-term follow-up study in which children were born in a randomized controlled experiment. Data was collected from 86% of FET and 80% of ET children through ASQ-3. The average age is 37 months, and there may be abnormal scoring when scoring. The purpose of the ASQ-3 questionnaire is to investigate the process of children's development, including five aspects: communication, gross motor, fine motor, problem solving, and personal social behavior. This is a quick way to identify children who do not meet health and developmental standards.