Assisted Reproductive Technology – Week 1 of Embryogenesis

by John McLachlan, PhD

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    00:00 Okay. That’s one of the things that can go wrong. But one of the things that can go right is the modern approach to assisted reproductive technology.

    00:11 Now that we understand these events relatively well, the possibility of intervening to help couples to have children has been very important, and since the first test tube baby has been born, there have been very many test tube babies that have brought joy to parents in a variety of different settings.

    00:30 So, in vitro fertilization is one of the key aspects of assisted reproductive technology.

    00:36 Here, what happens is that egg production is stimulated hormonally in the mother, and then some eggs are harvested. They’re actually removed under ultrasound guidance from the mother at stages when they’re capable of being fertilized. They are placed in a dish, not actually in a test tube of course but in a small millimeter dish filled with a rich culture medium. And then sperm from the father or from a donor is added to the dish and fertilization can take place within that dish itself. Subsequently, the eggs are observed. There may be video recorded in a real IVF clinic, for instance. And the ones which are developing well to schedule, you might be looking at them at the two-cell, four-cell stage to show that they’re dividing as normal as you would expect them to do, can then be returned to the uterus, and there, they will have a respectable chance of implanting and development taking place as normal. Nowadays, it’s traditional to transfer only one egg back into the uterus.

    01:48 Previously, more eggs were returned to the uterus and that meant that sometimes you got twin pregnancies or even triplet pregnancies if three eggs were returned. The reason that that’s no longer so popular is that twin pregnancies are always just a bit more challenging than a normal single pregnancy. So the risk of something going wrong with one, or indeed, both the twins is greater than it is with a single pregnancy. So in the early days, as this diagram shows, then perhaps three embryos might have been returned, but no, that’s actually much less common than it was done previously.

    02:31 In addition, you can help the process. As we’ll see in the fertilization lecture, it’s possible to actually inject sperm through the zona to ease their passage. Eating their way through the zona is quite a tricky task for the sperm, and it may be that some occasions of failure to conceive normally has been as a result of the sperm not being able to make its way through the zona. You could also inject a cell or inject the sperm directly into the egg. So it doesn’t even have to cross the cell membrane of the egg, and each of those gives ways in which the whole process of fertilization can be enhanced and advanced in appearance.

    03:16 You might not otherwise be able to do that spontaneously and naturally.

    03:22 You can also, at these early stages; you can screen for genetic defects and select which of the fertilized eggs will be re-implanted. So, that can be a choice. An easy one, for instance, would be to identify whether the developing pre-embryo is male or female in a family which is liable to, muscular dystrophy, Duchenne muscular dystrophy then it’s passed on through boys alone. So returning female pre-embryos to the uterus would mean that you do not have a child that suffered from muscular dystrophy of that particular kind.

    04:00 A recent development in the UK has been used of three parents’ IVF where the egg cytoplasm from one mother is combined with the nucleus from the second mother and sperm from the father, and that’s to avoid disorders of the mitochondria which are present in the cytoplasm.

    04:19 So, a radical new technique to avoid some inheritable defects.

    04:26 So, let’s summarize what we’ve looked at in this lecture. First of all, we looked at the early division stages, the cleavage stages in which the cells are getting smaller at each subsequent cell division.

    04:38 And then we looked at the process of hatching from the zona pellucida.

    04:43 Once it’s hatched from the zona pellucida, then the developing pre-embryo can implant into the uterine wall, and gradually, begin to eat its way under the surface. If this process takes place in the wrong place too soon, then we can have the serious risk of an ectopic pregnancy, which can, in fact, be life threatening. But the good news is the understanding this processes well as we do know, has allowed us to develop all kinds of reproductive technologies, which can bring childless couples the possibility of having natural children of their own.

    05:20 Thank you very much.

    About the Lecture

    The lecture Assisted Reproductive Technology – Week 1 of Embryogenesis by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Assisted Reproductive Technology – Week 1 of Embryogenesis

     John McLachlan, PhD

    John McLachlan, PhD

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