Category Archives: Human Reproduction

BACKGROUND

Prenatal screening and diagnosis of chromosomal abnormalities especially Down's syndrome in IVF pregnancies are complicated by higher maternal age, a high multiple pregnancy rate, a high risk of a vanishing twin and an increased risk of chromosomal abnormalities, particularly in pregnancies after ICSI. The aim of the present systematic review was to evaluate the findings of first trimester screening for chromosomal abnormalities in IVF/ICSI singleton and twin pregnancies.

METHODS

A systematic MESH-term search in MEDLINE using PubMed and the Cochrane Library was performed until May 2011, with no earlier date limit.

RESULTS

The electronic search retrieved 562 citations, 96 of which were evaluated in detail and 57 were then excluded for not meeting the selection criteria. A total of 61 articles were finally selected for review. Our analysis of the data shows that, for IVF/ICSI singletons, combined first trimester prenatal screening based on maternal age, nuchal translucency scan and biomarkers is appropriate. However, biomarkers seem to be altered, causing a higher false-positive rate, in IVF/ICSI singleton gestations. Correction factors have been developed and should be used when screening for Down's syndrome in singleton pregnancies. With regard to IVF/ICSI twin pregnancies, biomarker values seem to be dependent on chorionicity as well as gestational age. Whether the use of a correction factor for mode of conception in the risk calculations for Down's syndrome in twin pregnancies is valid has not been fully elucidated. In vanishing twin pregnancies with a second gestational sac with a dead fetus, first trimester screening should be based solely on the maternal age and the nuchal translucency scan as biomarkers are significantly altered in these cases.

CONCLUSIONS

First trimester prenatal screening after IVF/ICSI treatment requires specific precautions in both singleton and twin pregnancies.

Source:
http://humupd.oxfordjournals.org/rss/current.xml

BACKGROUND

Mitochondrial disorders are often fatal multisystem disorders, partially caused by heteroplasmic mitochondrial DNA (mtDNA) point mutations. Prenatal diagnosis is generally not possible for these maternally inherited mutations because of extensive variation in mutation load among embryos and the inability to accurately predict the clinical expression. The aim of this study is to investigate if PGD could be a better alternative, by investigating the existence of a minimal mutation level below which the chance of an embryo being affected is acceptably low, irrespective of the mtDNA mutation.

METHODS

We performed a systematic review of muscle mutation levels, evaluating 159 different heteroplasmic mtDNA point mutations derived from 327 unrelated patients or pedigrees, and reviewed three overrepresented mtDNA mutations (m.3243A>G, m.8344A>G and m.8993T>C/G) separately.

RESULTS

Mutation levels were included for familial mtDNA point mutations only, covering all affected (n = 195) and unaffected maternal relatives (n = 19) from 137 pedigrees. Mean muscle mutation levels were comparable between probands and affected maternal relatives, and between affected individuals with tRNA- versus protein-coding mutations. Using an estimated a priori prevalence of being affected in pedigrees of 0.477, we calculated that a 95% or higher chance of being unaffected was associated with a muscle mutation level of 18% or less. At a mutation level of 18%, the predicted probability of being affected is 0.00744. The chance of being unaffected was lower only for the m.3243A>G mutation (P < 0.001). Most carriers of mtDNA mutations will have oocytes with mutation levels below this threshold.

CONCLUSIONS

Our data show, for the first time, that carriers of heteroplasmic mtDNA mutations will have a fair chance of having healthy offspring, by applying PGD. Nevertheless, our conclusions are partly based on estimations and, as indicated, do not provide absolute certainty. Carriers of mtDNA should be informed about these constraints.

Source:
http://humupd.oxfordjournals.org/rss/current.xml

Unexplained recurrent miscarriage (RM) can be a challenging and frustrating condition for both patients and clinicians. For the former, there is no diagnosis available for consolation, while for the latter there is little evidence-based treatment to offer. However, the majority of these patients have an excellent prognosis without the need for any treatment. Epidemiological associations suggest that the reason for this is that the majority of women with unexplained RM are in fact healthy individuals, with no underlying pathology, who have suffered three miscarriages purely by chance. Nevertheless, a certain proportion of women with unexplained RM will continue to miscarry, and preliminary studies suggest the presence of pathology in some women of this group. As a result, two types of unexplained RM can be described: Type I unexplained RM, which occurs by chance in women who have no underlying pathology and has a good prognosis; and Type II unexplained RM, which occurs due to an underlying pathology that is currently not yet identified by routine clinical investigations and has a poorer prognosis. Distinguishing between Types I and II unexplained RM can be achieved by considering several factors: the age of the woman, the definition used for RM (i.e. whether biochemical pregnancy losses are considered as miscarriages), the number of previous miscarriages suffered and the karyotype of the products of conception, where available. A better understanding of the two types of unexplained RM could lead to more targeted referrals, investigations and treatments, which would improve cost-effectiveness and overall clinical care.

Source:
http://humrep.oxfordjournals.org/rss/current.xml

BACKGROUND

During pregnancy, maternal uterine spiral arteries (SAs) are remodelled from minimal-flow, high-resistance vessels into larger diameter vessels with low resistance and high flow. Fetal extravillous trophoblasts (EVT) have important roles in this process. Decidual natural killer cells (dNK cells) are the major maternal immune component of the decidua and accumulate around SAs before trophoblast invasion. A role for dNK cells in vessel remodelling is beginning to be elucidated. This review examines the overlapping and dissimilar mechanisms used by EVT and dNK cells in this process and how this may mirror another example of tissue remodelling, namely cancer development.

METHODS

The published literature was searched using Pubmed focusing on EVT, dNK cells and SA remodelling. Additional papers discussing cancer development are also included.

RESULTS

Similarities exist between actions carried out by dNK cells and EVT. Both interact with vascular cells lining the SA, as well as with each other, to promote transformation of the SA. EVT differentiation has previously been likened to the epithelial–mesenchymal transition in cancer cells, and we discuss how dNK–EVT interactions at the maternal–fetal interface can also be compared with the roles of immune cells in cancer.

CONCLUSIONS

The combined role that dNK cells and EVT play in SA remodelling suggests that these interactions could be described as a partnership. The investigation of pregnancy as a multicellular system involving both fetal and maternal components, as well as comparisons to similar examples of tissue remodelling, will further identify the key mechanisms in SA remodelling that are required for a successful pregnancy.

Source:
http://humupd.oxfordjournals.org/rss/current.xml

BACKGROUND

Pre-eclampsia, small-for-gestational-age infants, preterm birth and recurrent miscarriage complicate a significant number of pregnancies. The vascular endothelial growth factor (VEGF) family of angiogenic growth factors is implicated in the pathophysiology of these complications. We aimed to elucidate the role of these angiogenic factors in placentation and to evaluate the predictive value of their protein concentrations and genetic variations in pregnancy complications.

METHODS

We performed a systematic search of PubMed, and retrieved original articles. The search included a combination of terms such as VEGF-A, placental growth factor (PlGF), kinase insert domain receptor, fms-like-tyrosine-kinase receptor 1, soluble fms-like-tyrosine-kinase receptor 1, pre-eclampsia, small-for-gestational-age infants, preterm birth, recurrent miscarriage, placenta, prediction and polymorphisms.

RESULTS

This review summarizes the current knowledge of the roles of the VEGF family in early placentation and of the abnormalities in maternal plasma and placental expression of angiogenic proteins in adverse pregnancy outcomes compared with normal pregnancy. PlGF and sFLT-1 in combination with other clinical and biochemical markers in late first or second trimester appear to predict early-onset pre-eclampsia with a high sensitivity and specificity. However, VEGF family proteins do not have sufficient power to accurately predict late-onset pre-eclampsia, small-for-gestational age pregnancies or preterm birth. Functional polymorphisms in these angiogenic genes are implicated in pregnancy complications, but their contribution appears to be minor.

CONCLUSIONS

Although the VEGF family has important roles in normal and complicated pregnancy, the current predictive value of the VEGF family as biomarkers appears to be limited to early-onset pre-eclampsia.

Source:
http://humupd.oxfordjournals.org/rss/current.xml

BACKGROUND

Spermatogenesis culminates in production of one of the most highly differentiated cells in biology, the spermatozoon. The gametes that emerge from the testes are, however, functionally immature and only acquire full functionality once they have completed a process of post-testicular maturation in the epididymis and female reproductive tract. Remarkably, this acquisition of sperm function occurs while these cells are transcriptionally and translationally silent and is therefore highly dependent on post-translational modifications to their existing protein complement. In this review, we consider the emerging roles of several prominent molecular chaperone families in orchestrating both the morphological differentiation of male germ cells during spermatogenesis and their functional transformation during sperm maturation.

METHODS

Journal databases were searched using key words, including chaperone, heat shock protein, testes, spermatogenesis, spermatozoa, epididymal maturation, capacitation and fertilization.

RESULTS

In the past two decades, molecular chaperones have been acknowledged to play key roles in controlling both the morphological transformation of germ cells during spermatogenesis and the post-testicular maturation of these cells as they transit the male and female reproductive tracts. Furthermore, there is mounting evidence that aberrant chaperone expression may be a major contributing factor to the defective sperm function seen in many cases of male infertility.

CONCLUSIONS

Molecular chaperones are critically involved in all phases of sperm development. Targeted disruption of these proteins has the ability to arrest spermatogenesis, compromise sperm maturation and inhibit fertilization. These proteins therefore hold considerable promise as targets for novel contraceptive strategies and as diagnostic biomarkers for male infertility.

Source:
http://humupd.oxfordjournals.org/rss/current.xml