Introduction

The process of fertilizing human gametes outside of the body has revolutionized how we approach infertility. This breakthrough allowed embryos to be developed in vitro and then implanted in the mother’s uterus, resulting in live births. To date, millions of births have occurred thanks to the development of in vitro fertilization (IVF) [1]. One critical step in the IVF process is ensuring that the implanted embryo is disease-free, which significantly increases the chances of a successful pregnancy. However, despite the significant advancements in the technique, the effectiveness of the implantation process remains a challenge, which can ultimately affect the success of pregnancy [2].

Preimplantation genetic testing (PGT) allows for identifying abnormal embryos so that only genetically normal embryos are transferred. PGT has become vital to Assistive Reproductive Technology (ART) procedures [3].

Since the 1990s, when Handyside, and his colleagues published a successful report of birth after PGT for detecting Y-chromosomes repetitive sequences for gender determination in families having X-linked diseases, the process has developed into a complete experimental protocol. It has led to the successful alternative method for prenatal diagnosis and prevention of termination of pregnancy [4]. The oocytes and embryos are tested in any PGT framework for the assurance of transferring only the disease-free embryos to the uterus. This results in the successful birth of unaffected children when comes to genetic diseases [5].

This process of PGT involves two main techniques, preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS), which are applied to the cells after removing them from early embryos before their implantation into the receptive uterus. Among them, PGD is the diagnosis of abnormal genetic features, such as abnormal rearrangements of chromosomes or specific mutations that may be present in the embryos, especially when any parent or both parents carry genetic rearrangements or mutations. PGS, on the other hand, screens embryos for the presence of chromosomal aneuploidy. This is particularly useful in cases with complications like recurrent pregnancy losses or advanced maternal age. As in vitro culturing techniques have been developing during the last 40 years, the process of embryo biopsy has been extended to different stages of the development of embryos. These include testing for the polar body (PB), the cleavage stage of 1–2 blastomeres, and the blastocyst-stage testing, where trophectoderm stage cells can be tested from the developing embryo. Genetic and chromosomal testing has also advanced to the analysis using small quantities of DNA. For this purpose, polymerase chain reaction (PCR), fluorescence in situ hybridization (FISH), and microarray analysis have been developed. This analysis has been extended to array comparative genomic hybridization (aCGH), next-generation sequencing (NGS), and detection of single nucleotide polymorphisms (SNP) [6].

In this review, we have summarized the current advances in preimplantation genetic testing of embryos and the discrepancies that still need to be addressed. We also shed some light on the future of the process and the importance of the techniques used for achieving a successful pregnancy.

Background and history

Even though the first known use of PGT was not until 1990, the technology has a long and fruitful history.

Scientists first considered IVF a potential infertility treatment in the late 1960s. This process required fertilizing an egg outside the body and inserting the developing embryo into the mother's uterus. Unfortunately, it became apparent that not all embryos were viable and that many would fail to implant or end in miscarriage as IVF procedures progressed.

As a result, PGT was developed to help clinicians choose out embryos with genetic flaws that might cause implantation failure, miscarriage, or even more severe genetic problems. In the 1990s, the first PGT method, fluorescent in situ hybridization (FISH), was created. In FISH, fluorescent probes are used to identify particular DNA sequences, allowing for the screening of embryos for genetic disorders like Down syndrome.

Several alternative PGT methods, such as polymerase chain reaction and comparative genomic hybridization (CGH), have been developed throughout time. Screening for genetic diseases, including cystic fibrosis, sickle cell anemia, and Huntington's disease, became possible because these approaches allowed for more thorough genetic testing.

Next-generation sequencing (NGS) is a novel method that has arisen in recent years that allows for the simultaneous screening of embryos for hundreds of genetic diseases. Because of this, PGT is now more widely available and reliable than ever before, allowing couples with a family history of genetic diseases to conceive healthy children [7].

PGT has been a game-changer for families dealing with infertility and genetic diseases. Still, it has also been a controversial issue owing to ethical concerns and discussions about the use of reproductive technology. Timeline and history of PGT is summarized in Table 1.

Table 1 Timeline and history of PGT
Full size table

Assisted fertilization

It was not until 1986 that zona drilling, before insemination, was used as a successful form of micromanipulation to aid fertilization in the mouse. The micromanipulator was used to spray acidified Tyrode's solution onto the zona, causing focal zona breakdown and facilitating spermatozoa access to the oolemma [31]. Following using a mechanical version of zona drilling in 1988, children were born to male-factor infertile couples [32]. This marked the first time a micromanipulator had been used to establish a human pregnancy successfully. In the same year, groups in Singapore and Rome (Italy) reported successful spermatozoa injections into the perivitelline space. There was no fast block to polyspermy on the membrane level. Therefore, fertilization rates were low even though both procedures enhanced the chances of treating more severe types of male-factor infertility. After successful monospermic fertilization; however, implantation rates were comparable to or higher than those seen with conventional insemination. ICSI is currently being utilized more frequently, and in some situations, it is completely replacing traditional insemination. While effective in terms of pregnancy and live birth rates, the logic of using ICSI without discrimination when it is unnecessary is still up for dispute.

Intracytoplasmic sperm injection

The process of a single spermatozoon into the cytoplasm of an oocyte is called Intracytoplasmic sperm injection (ICSI). This technique involves the use of a glass micropipette injection. This method was introduced in the late 1990s as a modification of the process of in vitro fertilization (IVF) [16]. Along with assistive reproductive technology (ART) and IVF, this technique has enabled men suffering from azoospermia or with low quality and quantity of sperm to become a father to a child [33].

Originally, the ICSI technique was developed for treating severe cases of male infertility, and since then, it has been recognized as a well-established method for treating male infertility. Although, over the years, the rate of diagnosis of couples having male-factor infertility has remained stable, the proportion of successful fertilization has steadily increased, indicating the success of the process [34]. To the best of our knowledge, a specific study for elucidating the success of this technique for successful fertilization in couples suffering from male-factor infertility has not been conducted, the fact remains that this technique has been widely used [35, 36]. It has been discussed that widespread use of this technique may lead to adverse health results in the offspring [37]. However, ICSI still exists as a promising tool for solving the problem of male infertility. Figure 1 below shows the process of ICSI.

Fig. 1
figure 1

Figure showing intracytoplasmic spermatozoon injection into the oocytes. Figure adapted from [38]

Full size image

In vitro fertilization (IVF)/in vitro diagnostic procedures

Several ethical as well as scientific challenges have been faced by research involving human reproduction. In the decades of 1960 and 1970, our understanding of oocyte fertilization and the human reproductive system paved the way for in vitro fertilization (IVF) development. The process ultimately resulted in the birth of the first test tube baby in 1978 [11]. In this technique, laparoscopy was used to retrieve pre-ovulatory oocyte from the mother’s ovary that underwent a normal menstrual cycle. It was fertilized in vitro, and then an eight-cell embryo was transferred to the mother’s uterus. Within 3 years of this development, 15th baby was born worldwide and the first in the US alone. Instead of relying on the natural production of a single oocyte, the human menopausal gonadotropin was injected to produce several oocytes through the ovary follicles. The process has been termed controlled ovarian stimulation (COS). In this process, laparoscopy retrieves pre-ovulatory oocytes, and then in vitro fertilization is performed. After about 3–5 days, the embryo is transferred into the mother’s uterus.

Over the years, this technique has developed at an increased pace. It accounts for millions of births globally every year. In US and Europe, every year, 1 to 3% of all births are attributed to IVF [39]. Research and development have extensively focused on the optimization of techniques for the success of IVF. A majority of infertile couples undergo IVF treatment. This results in the birth of a genetically related child to them. With research development, embryos are also tested for detecting any disorders. In such cases, single gene mutations are prevented, which can result in morbidity [40, 41]. In addition, using oocytes and donor sperm has become popular. Gestational carriers are also used for women who are unable to carry pregnancy.

Traditional invasive biopsy techniques

Biopsies of polar bodies, blastomeres, or trophectoderm cells have proven useful in PGT, allowing hundreds of families to have healthy pregnancies [42]. At ovulation, mature oocytes extrude the first polar body (PB), and the second PB develops following fertilization. The PBs are waste products of meiosis, serving as storage sites for the chromosomes lost by the oocyte during its transformation into a haploid state. The removal of both PBs for PGT is sometimes seen as less intrusive than procedures involving the biopsy of cells at later embryonic stages because they appear to play no function in subsequent development and are not a fundamental part of the embryo [43]. However, PB analysis has apparent drawbacks, the most notable being its inability to shed light on the paternal role in the embryo's genetic makeup. Even though many of the resultant embryos would eventually arrest in culture, the process is still labor intensive because of the necessity to biopsy and analyze all of the mature oocytes generated. It has been found that even this seemingly non-invasive procedure, PB biopsy, might have a deleterious effect on embryo viability, as it has been linked to increased incidences of embryo fragmentation and developmental arrest [44].

Preimplantation genetic screening using embryo biopsy

In the early days of PGT, the most common biopsy method entailed removing one to two blastomeres from an embryo at the cleavage stage. This was commonly done on day 3 when the embryo normally consists of 6 to 10 cells. But this tactic does have a few drawbacks to consider. Firstly, chromosomal mosaicism, which is prevalent during all stages of preimplantation development, reaches its peak frequency at the cleavage stage. This has the potential to cause errors throughout the PGT-A process. [45]. Second, allelic dropout (ADO), the inability of one of the two alleles present in a heterozygous cell to amplify following PCR, greatly increases the likelihood of genotyping errors at particular sites during PGT-M cycles when analyzing a single cell. An ADO occurs in 5–10% of single-cell amplifications on average [46]. Due to this issue, more sophisticated, redundant diagnostic methods that combine mutation detection with the examination of numerous useful related polymorphisms have had to be developed.

Human embryos at this early stage are anticipated to exhibit a high degree of developmental plasticity and tolerate the loss of cells since the cleavage stage cells are often considered totipotent. Yet, recent research indicates that mice's four-cell stage exhibits some degree of cell fate specification [47]. In the case of human embryos, if specification processes begin at an equally early level, removing cells meant to contribute to the fetus during cleavage stage biopsies could be detrimental to the developing fetus. According to this theory, multiple investigations have found that blastomere biopsy can affect embryo viability and change preimplantation morphology [48,49,50]. Single blastomere biopsy has been shown to reduce implantation rates by 39% relative to controls in a randomized controlled experiment (RCT) [51].

Very little long-term data on the health of people born from embryos that had a biopsy at the cleavage stage is available, but what is available is promising [52, 53]. Nonetheless, it is worth mentioning that mice conceived via blastomere biopsy have shown increased susceptibility to neurological diseases, larger-than-average bodies, and epigenetic alterations [54, 55].

Blastocyst biopsy, typically done on day 5 after fertilization, was a significant advance [56]. Blastocysts have a greater tolerance for micromanipulation and are more robust than early-stage embryos. Although less of the embryo is lost during a trophectoderm biopsy than during a cleavage stage biopsy, more genetic material can be retrieved. Because of the larger amount of DNA available, the chances of amplification failure and ADO are decreased, and chromosomal mosaicism can be detected in some cases within the framework of PGT-A [57,58,59,60]. The great majority of embryo biopsies performed today for PGT are performed using the blastocyst biopsy approach, which gained popularity when it was reported to be safer for the embryo than the removal of blastomeres [61,62,63].

Yet, in the haste to perform blastocyst biopsies, it is probable that some hazards linked with this approach have been neglected. Embryo viability may be jeopardized by improper execution of biopsy processes, which continue to be technically hard, invasive operations. Taking more cells from the trophectoderm during a biopsy has been linked to a lower birth rate than taking a smaller number of cells [64]. The theory goes that less invasive methods of collecting DNA for PGT should pose less danger to developing embryos. Furthermore, such techniques may make it possible to analyze embryos of poor morphological grade that are typically rejected without ever getting genetic investigation since they are deemed unfit for biopsy. Figure 2 below shows the process of biopsy from the embryo.

Fig. 2
figure 2

The process of trophectoderm cells biopsy from the blastocyst. Figure adapted from Ashley & Emily, 2017 [65]

Full size image

Follow-up of babies after assistive reproductive techniques

Epigenetic and imprinting issues, as well as neurologic sequelae (poor learning ability and language barrier), have been linked to ART children compared to conceived children, according to some investigations [66,67,68,69,70], and particular anomalies, such as epilepsy or convulsions, unidentified infections, and parasite diseases, asthma, genitourinary diseases are also related to ART [71, 72]. They may be at significant risk of developing metabolic syndrome (obesity, type 2 diabetes, and hypertension) as adults due to the increased prevalence of LBW or VLBW, preterm, and IUGR [66]. IVF-conceived children aged 8 to 18 had greater blood pressure than normally conceived children, according to Ceelen et al. [73]. In contrast to naturally generated placentas, ART-derived placentas have distinct ultrastructure and gene expression profiles, which may impact the offspring’s health [74]. The mechanisms underpinning the negative health risks of offspring conceived by ART are yet unknown. It is also uncertain if the potentially elevated health risk is brought on by ART or some other factor related to infertility [75].

Most recent research has focused on the likelihood that children conceived through ART get hospitalized for respiratory tract infections. As a result, less serious infections that are managed in primary care or that do not require the assistance of medical professionals are rarely included in the studies. It is uncertain whether the likelihood of respiratory infections in ART-born children varies depending on the medically assisted conception method [76, 77]. Few studies have tried to determine if any observed increased risks are due to factors connected to the underlying parental subfertility [77,78,79,80]. Children conceived by ART experience more illnesses and are more likely to spend early childhood hospital stays due to respiratory tract infections [81]. Another study found that ART conception was linked to higher risks for all types of hepatic tumors, leukemias, and pediatric cancers regardless of comparison to natural conception or subfertility without ART. Preterm birth and low birth weight did not act as mediating factors in these correlations. Although there have been reports of an elevated risk of childhood cancers, the frequency of occurrence is still relatively low. [82].

Aneuploidy, mosaicism, and other structural rearrangements

A single embryo transfer is the goal of the modern fertility clinic to have a healthy baby (SET). In the past, it was normal practice in the ART industry to transfer two or more embryos simultaneously, which could lead to multiple pregnancies and their accompanying clinical issues [83, 84]. When a patient undergoes in vitro fertilization (IVF), multiple embryos may develop and be ready for transfer. The difficulty then becomes determining how to rank the embryos in the cohort from best to worst. Since the beginning of IVF, embryos have been graded based on how healthy they appear to be [85]. Embryonic morphological evaluation standards are greatly enhanced, yet there are still some limitations [86]; the fact that morphology alone has been proven to be a poor predictor of implantation, the procedure is nonetheless performed subjectively [87]. As it was realized that many early human embryos have chromosomal abnormalities, chromosomal profiling to eliminate embryos with copy number and structural defects became a promising option. By taking a small cellular sample from each embryo and studying it with molecular techniques, doctors could determine the XX/XY status of patients carrying hereditary X-linked diseases for the first time [4]. This established the feasibility of autosomal profiling for clinical use and paved the way for the creation of PGT for aneuploidy (-A) and structural rearrangements (-SR). The use of PGT-A/-SR has skyrocketed over the past 2 decades, and it is now standard procedure in many countries alongside ART cycles [88]. There are some outspoken detractors of the technology, not all of the clinical data from PGT-A has been encouraging. When the technology's limitations are taken into account; however, there are compelling arguments for PGT-A's appropriate application.

Currently, PGT-A is dramatically changing how it classifies embryos based on their chromosomal patterns. Normal and abnormal can no longer be used as categorical opposites anymore. The evidence presented here supports a more nuanced classification, including mosaic and segmental aberrant embryos in addition to those that are euploid, aneuploid (whole chromosomes, such as monosomy or trisomy), and aneuploid. Characteristics can also be used to categorize patients into mosaic and segmental aberrant groups. This sorting aims to arrive at a better ranking system for picking the embryo most likely to have a healthy outcome in the long run [89]. At this juncture in its evolution, PGT-A technology will be shaped by two seemingly conflicting forces: simplicity and complexity.

On one hand, there is an effort to streamline the procedure by creating a non-invasive model, which would make the laboratory sample-collecting stage more streamlined and hence more accessible to fertility clinics (but importantly, at the potential expense of data quality). On the other hand, there is a need for more nuanced information, which can be attained by improving genome resolution, integrating multiple genetic analyses (such as copy number and B-allele frequencies, or chromosomal and single gene profiling), or, ultimately, sequencing the entire genome of a candidate embryo. While the future of PGT-A and its many variants remains unclear, one thing is certain: the ‘genetic revolution’ has already revolutionized embryo selection in IVF and will continue to do so for years to come [89].

PGT can detect aneuploidy, chromosomal structural rearrangements (PGT-SR), and monogenic diseases or single gene abnormalities (PGT-A) [90]. The process of PGT begins with a biopsy of a single cell or a small number of cells from an in vitro fertilized embryo, continues with testing of the biopsied samples for genetic abnormalities, and concludes with the selective transfer of embryos unaffected by the condition under study. Yet, it is difficult and time-consuming to do genetic testing on a single cell or a small number of cells. Multiplex PCR testing, in which closely connected informative short tandem repeat (STR) markers are co-amplified, with or without the pathogenic variant amplicon, quickly supplanted the single cell simplex PCR used in this early PGT-M technique. The detection of monogenic diseases has shifted toward a single-cell biopsy on day 3 followed by multiplex PCR [91]. Over the past decade, blastocyst-stage biopsy and genome-wide technologies have begun supplanting this previously accepted standard. Genome-wide techniques provide information on genotyping and chromosome copy number, for PGT-M and PGT-A to be analyzed together [92,93,94,95,96].

Due to the technological complexity of PGT and PGT-M, transport PGT was developed, which involves sending biopsied embryo samples from a satellite IVF laboratory to a genetics center for analysis. To its credit, transport PGT testing can be carried out by seasoned groups in genetic laboratories specializing in single-cell molecular diagnostics. Despite transportation and (international) collaboration difficulties, transport PGT as a service has grown significantly [97].

Several international organizations, including the PGD International Society (PGDIS), the American Society for Reproductive Medicine (ASRM), and the European Society of Human Reproduction and Embryology (ESHRE) PGT Consortium, have developed standards and recommendations for excellent practice in PGT. The latter organization has recently revised and expanded on four sets of recommendations, including those addressing how PGT services should be structured and how to conduct embryo biopsy and genetic testing [97,98,99,100].

A summary of clear indications for PGT is presented in Table 2 below:

Table 2 Preimplantation genetic testing (PGT) indications summary
Full size table

Techniques used for preimplantation genetic testing

When comparing the genetic material from a biopsy to a reference sample, the aCGH method can detect differences in the number of copies and rearrangements of each of the 24 chromosomes. WGA amplification is followed by fluorescent probe labeling and hybridization to a DNA microarray. Chromosomal loss or gain can be determined by observing each spot's color change following hybridization. To analyze aneuploidy and chromosomal rearrangements, a laser scanner and data processing software are employed to detect fluorescence [101].

An array setup including DNA hybridization, fluorescence microscopy, and solid surface DNA capture is used to conduct a single nucleotide polymorphism array (SNP). The ploidy status of the sample is determined by comparing the SNPs detected in the analysis to the corresponding SNPs from the mother and father [102].

Real-time quantitative polymerase chain reaction (RT-qPCR) may determine the copy number of each chromosome, allowing for the identification of the entire chromosome's asset. Three or four locus-specific amplicons are generated along each chromosome, and these amplicons are compared to a reference gene on the same chromosome to estimate the copy number. The only chromosomal abnormality it can detect is triploidy; chromosomal abnormalities and uniparental disomy are beyond its capabilities [103].

The most modern technique for PGT is Next Generation Sequencing (NGS). WGA, similar to aCGH, is the starting point of this procedure. When the genome has been amplified, a bar-coding method assigns unique sequence labels to each sample. Based on the sequencing platform used, this method can reduce the cost per sequenced embryo by as much as a factor of ten. Copy number variations and significant deletions or duplications are then identified by comparing each sequence to a reference human genome using specialized software [104,105,106].

Several molecular approaches are now available, which has sparked a discussion regarding whether or not they are sensitive and reliable enough for PGT. Women who underwent NGS had a considerably higher implantation rate (71.6%) and continued pregnancy/live birth rate (62.0%) than women whose results were determined using aCGH (64.6% and 54.4%, respectively), as revealed in a study by Friedenthal et al. The NGS group had a lower rate of biochemical pregnancies (8.7%) than the aCGH group (15.1%), and both groups had a similar rate of spontaneous abortion (12.4%). These results led the authors to conclude that PGT utilizing NGS considerably improves clinical outcomes compared to aCGH. They also suggested that NGS would be more useful than aCGH in identifying mosaic embryos and partial aneuploidies or triploidy [27].

The clinical error rates in frozen-thawed embryo transfer (FTET) cycles of a single euploid embryo identified by NGS (1151 cases) and aCGH (846 cycles) were analyzed by Friedenthal et al. Clinical error rates were reduced in the NGS group compared to aCGH: 0.7% vs. 1.3% for each embryo, 1% vs. 2% for each pregnancy with gestational sac, 0.1% vs. 0.4% for continued pregnancy/live birth rates, and 13.3% vs. 23.3% for spontaneous abortions [107]. Consequently, despite the fact that NGS and aCGH are highly sensitive techniques for PGT, doctors must nevertheless consider the possibility of errors.

It has been suggested that informed consent and patients’ counseling in a comprehensive manner are very important when taking PGT-A. Although there are potential benefits of this procedure; however, the benefits need to be balanced against various limitations the procedure possesses. These include the risk of false positive results, a risk of damaging the embryo, along with embryo mosaicism [108]. It is imperative to consider that the birth of newborn after negative results of PGT-A can also lead to the birth of individual having genetic abnormalities [109]. Meng et al., 2023, analyzed 107 samples using Raman spectroscopy for the evaluation of composition of the discarded medium from 53 embryos that resulted in successful pregnancies and 54 which did not resulted in pregnancies. In this study, D3 cleavage stage culture medium from the embryos were studied using Raman spectra. A prediction about the developmental potential of embryos was made using machine learning tools and an accuracy of 71.5% was obtained. This study provided an evidence for using noninvasive tools for PGT-A and avoiding false positive and negative results [110]. It has been observed that 5% reduction in live births in PGT-A occurs because of damage to embryo caused by biopsy related procedures, and false positive results occurring due to various technical errors [111, 112].

Selection of embryo is routinely performed based on morphological assessment but as there is no such correlation between genetic abnormalities and morphological characteristics; therefore, this technique can also result in possibility of genetic abnormalities [113,114,115]. In the past decade, non-invasive approaches for PGT-A have been widely applied which include the use of cell free DNA from the spent embryo culture media (SECM) that provides an opportunity for extraction and sequencing of genetic material. The results of such studies have been found similar to the invasive PGT-A [116]. Several biological markers are being explored as a prospective candidate for developing the non-invasive PGT-A further. These include the use of extracellular vesicles which are released at all stages of embryo development in surrounding media, and embryos use these vesicles for communicating with the surrounding environment. [117,118,119]. Another important marker are miRNAs, which can be easily detected, recognized and used for analysis, and several studies have suggested their importance in developing non-invasive PGT-A [120,121,122,123]. Several approaches are currently being explored in a quest to develop standardized noninvasive testing procedures for PGT-A [124]. The use of computational biology, machine learning, and artificial intelligence is also being explored with promising results [125].

Embryo preservation

Many revolutionary technologies have been implemented and polished in the IVF laboratory over the years. Cryopreservation of oocytes and embryos, assisted fertilization for treating male-factor infertility, preimplantation genetic diagnosis of embryos, and creating new embryo selection methodologies and platforms, such as embryo morphokinetics using time-lapse microscopy, have all played crucial roles [1].

Cryopreservation

In 1949, Chris Polge and his colleagues were the first to freeze mammalian spermatozoa successfully cryogenically. It was not until a few years later when Raymond Bunge and Jerome Sherman froze human spermatozoa in Iowa (USA). The freezing of cleavage stage mouse embryos by David Whittingham, Stanley Leibo, and Peter Mazur in 1971 revolutionized the science of embryology [126]. Beginning in the early 1980s, the human embryo was cryopreserved at every developmental stage, from the zygote to the formed blastocyst, with only modest modifications; however, survival rates remained below 80% for many years. This endeavor had a solid scientific basis; basic scientists working with rodents and agricultural animals had long before perfected the technology. Oocyte and embryo cryopreservation have come a long way in the last decade thanks to the development and widespread use of vitrification. Clinical benefits of delayed transfer in natural rather than stimulated cycles are more apparent now that approximately 100% survival rates are achieved using treatment regimens involving cryopreservation of all embryos and oocytes [1].

Conclusion and future perspectives

In conclusion, PGT has emerged as an invaluable resource for parents hoping to start a family with a reduced risk of genetic disorders. PGT identifies genetic abnormalities and chromosomal anomalies in embryos before they are placed in the uterus, which can aid in lowering the probability of passing such diseases to future generations.

There are a few different kinds of PGT, each with its own set of potential uses and restrictions: PGT-A, PGT-M, and PGT-SR. It is important to weigh the pros and downsides, which are mentioned below, of PGT thoroughly before deciding whether or not to have the treatment done.

Pros of preimplantation genetic testing (PGT)

  • Decreases the likelihood of passing on genetic problems to future generations by allowing the detection of embryos with genetic defects by PGT.

  • PGT permits the selection of viable embryos, which raises the probability of a healthy pregnancy and a live birth.

  • Aneuploidies, the most common cause of miscarriage, may be detected by PGT, allowing for selecting embryos with a normal set of chromosomes.

  • Enables the selection of embryos free of specific genetic abnormalities by detecting specific genetic mutations.

  • Using PGT for gender selection, parents can have children of both sexes, creating a more equitable household.

Cons of preimplantation genetic testing (PGT)

  • PGT is not always precise and can result in false positives or false negatives.

  • Unfortunately, not many couples trying to conceive through IVF can afford PGT because of its high cost.

  • Using PGT for non-medical purposes, such as sex selection or selecting particular features, presents ethical considerations.

  • Embryonic biopsies, performed as part of PGT, are invasive procedures that pose little danger to the developing embryo.

  • PGT can be emotionally stressful for couples since they may feel pressured to select the “right” embryo and may experience emotions of guilt or regret while deciding to reject embryos with genetic defects.

Future perspective

Future improvements in PGT technology and methodologies promise more reliable and time-saving ways to screen for and diagnose genetic disorders in embryos. As our knowledge of genetics and genomics expands, and more genetic data become available, PGT may also become more useful in detecting a broader spectrum of genetic illnesses.

Single-cell RNA sequencing (scRNA-seq) has been used recently to identify the factors that control early embryo development and oocyte maturation in humans. Nowadays, scRNA-seq has emerged as a different method for analyzing the transcriptome in early human embryos. Recent studies have shown that mRNA clearance or zygotic gene transcription failure influences the development of human preimplantation embryos. When preimplantation genetic diagnosis (PGD) is carried out in a clinical study, the analysis of transcriptions may be employed as a new criterion to forecast the embryo’s potential for development. The changes in gene expression found in human 8-cell embryos are closely related to their capacity for development. They may serve as targets for enhancing embryo development or indicators of the embryo's development. [30].

Maybe even more concerning are the ethical and societal concerns that arise when PGT is applied to characteristics that have nothing to do with health, such as appearance, intelligence, and personality. To ensure PGT is being used in a way that does not conflict with moral norms, we must continue having thoughtful talks and debates about it.

In conclusion, PGT has greatly improved our capacity to detect and lessen the likelihood of passing on genetic abnormalities to future generations. PGT will remain an important tool in the fight against genetic abnormalities and for the betterment of reproductive health so long as it is subjected to rigorous scientific and ethical scrutiny.