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Placenta is the first organ to form in a fertilised egg

Placenta is the first organ to form in a fertilised egg

Placenta development is initiated first in human pregnancies, even before the embryo starts to form, according to new research.

A team of scientists at the Francis Crick Institute, London, has found that one of the first steps after egg fertilisation in mammals is the initiation of placenta creation, the organ responsible for providing oxygen and nutrients to the growing baby.

‘This study highlights the critical importance of the placenta for healthy human development,’ said Dr Kathy Niakan, senior author of the study and group leader at the Crick. ‘If the molecular mechanism we discovered for this first cell decision in humans is not appropriately established, this will have significant negative consequences for the development of the embryo and its ability to successfully implant in the womb.’

Once an egg is fertilised the cell rapidly divides and a key process called cell specialisation occurs, where each cell is assigned a specific task.

The team sought to examine the very first cell specialisations by studying donated human embryos that were surplus to in vitro fertilisation (IVF) treatment.

In embryos at the 16-32 cell stage, the team observed a subset of cells which changed shape and polarised, this triggered molecular events that drives placenta specialisation. In particular, atypical protein kinase C (aPKC) was highly expressed at one end of the cell, when aPKC was inhibited the cells no longer became placenta precursors.

This first cell specification is ‘widespread in mammals’ said researchers after they found the same result in cow and mouse embryos, which have divergent mechanisms at later stages of development.

This research, published in Nature, revealed that placenta development starts much earlier than previously thought, before the embryo has implanted into the wall of the uterus, suggesting placenta cells may have important functions in healthy embryo implantation and development.

During IVF treatment, a reliable predictor of successful implantation of an embryo is the presence of placental precursor cells under the microscope. Therefore, this work paves the way towards a better understanding of how to help those struggling to conceive.

‘Understanding the process of early human development in the womb could provide us with insights that may lead to improvements in IVF success rates in the future’ adds Dr Niakan, ‘It could also allow us to understand early placental dysfunctions that can pose a risk to human health later in pregnancy.’

Read more: https://www.nature.com/articles/s41586-020-2759-x

Source: https://www.bionews.org.uk/page_152173

What are your chances of having a second IVF baby after fertility treatment for the first?

What are your chances of having a second IVF baby after fertility treatment for the first?

Women have a good chance of having a second child with the help of fertility treatment after the birth of their first child born this way, according to the first study to investigate this, published today in Human Reproduction, one of the world’s leading reproductive medicine journals.

Researchers in Australia calculated that after a woman successfully achieved a live birth using in vitro fertilisation (IVF), also known as assisted reproductive technology (ART), the chances of a second ART baby were between 51% and 88% after six cycles of treatment.

These calculations depended on whether or not previously frozen embryos were used or fresh embryos from a new ovarian stimulation cycle, and on assumptions made about the likely success rate for women who discontinued treatment.

The chances of a second ART baby decreased with increased maternal age.

Compared to women younger than 30 years, the likelihood of women aged 35-39 having a second ART-conceived baby reduced by 22% if they recommenced treatment with a frozen embryo from a previous cycle and by 50% if they recommenced treatment with a new cycle and a fresh embryo.

Factors that improved their chances of a successful second pregnancy included requiring only one cycle and a single embryo transfer to achieve a first live birth, and where infertility was caused by factors affecting the male partner.

Professor Georgina Chambers, director of the National Perinatal Epidemiology and Statistics Unit at the University of New South Wales (Sydney, Australia), looked at data from 35,290 women who received ART treatment between 2009 and 2013 in Australia and New Zealand and had a live baby during this time. These women were followed for a further two years to 2015, providing between two and seven years of follow-up data, and live births up to October 2016 were included.

We calculated two measures: what is a woman’s chance of achieving a second live birth in a particular cycle of treatment if previous cycles have failed, for instance in cycle three if the first two cycles have failed; and what is the overall, or cumulative, chance of a woman achieving a live birth after a particular number of cycles, including all the previous cycles. For example, what is the overall chance of a woman having a baby after up to three cycles,” said Prof Chambers.

A cycle includes the stimulation of the ovaries to mature multiple eggs, the collection of eggs for fertilisation in the laboratory to create embryos, and then all embryo transfer procedures that use the embryos from the egg retrieval procedure. This can include fresh embryo transfers and frozen embryo transfers.

Prof Chambers and her colleagues calculated estimates of cumulative live birth rates (CLBR) for women who were trying for a second ART baby that took account not only of the women who continued treatment, but also those who discontinued treatment.

The conservative CLBR assumed that women who dropped out would have no chance of achieving a second live birth if they had continued treatment. The optimal CLBR assumed these women would have the same chance of a live birth in a particular cycle as women who had continued treatment. The range between the conservative and optimal estimates gives a realistic idea of success rates.

Just over 43% (15,325) of the 35,290 women, with an average (median) age of 36, returned for treatment to conceive a second child by December 2015.

Among these women, 73% used a frozen embryo from the egg retrieval cycle that had resulted in their first child, and for them the CLBR ranged from 61% (conservative estimate) to 88% (optimal estimate) after six cycles. Among the women who had a new stimulation cycle and used a fresh embryo, the CLBR ranged from 51% to 70%.

Overall, 43% of women who recommence treatment with one of the frozen embryos from a previous stimulation cycle will have a baby after their first embryo transfer procedure. Between 61% and 88% of these women will have a baby after six cycles,” said Prof Chambers. “Among those who recommence treatment with a new stimulation cycle and a fresh embryo transfer, 31% will have a baby after their first cycle and between 51% and 70% after six cycles.”

Although success rates declined with female age, the researchers found that after three cycles of treatment, the conservative and optimal CLBRs in women aged 40 to 44 years were 38% and 55% respectively in those that started with a frozen embryo, and 20% and 25% in those recommencing with a new stimulated cycle and fresh embryos.

Read more: https://academic.oup.com/humrep/advance-article/doi/10.1093/humrep/deaa030/5817569

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