Role of Prenatal Diagnosis – Weeks 3-8 of Embryogenesis

by John McLachlan, PhD

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    00:01 it might appear to be. So, what can we do about this, and where this prenatal diagnosis comes in? There is a variety of things that we can now do. For instance, amniocentesis, ultrasound scans, chorionic villus sampling, where we can look at what’s happening during the course of the pregnancy and this can give us various options, which I’ve listed on the left-hand side of this picture. At the top, I put termination, and this can have a significant impact on the frequency of a developmental abnormality. I’ve listed data for Paris, Glasgow, and Dublin for dystrophic conditions. That’s neural tube defects.

    00:41 At first glance, you can see that the incidence is much lower in Paris than it is in Glasgow or Dublin. In fact, this kind of neural tube defects was sometimes called the Celtic curse.

    00:54 There may well be differences in the regional distribution of the abnormalities and which reflects different genetic backgrounds in the population. Or perhaps, it reflects different kinds of deprivation that you get in these areas. But Glasgow and Dublin are very similar in the incidence per 10,000 live births. But in Scotland, termination of pregnancy is legal, whereas, in the Republic of Ireland, it’s still something which is much more difficult for legal and cultural reasons. So you can see that the live birth rate of babies with a dysgraphic neural tube defect in Glasgow is about 10 or 11 and in Dublin, it is about 24, 25 even though the incidence is very similar. So, termination of a pregnancy, when a significant abnormality has been detected, is one option, and that reduces the incidence of live births quite significantly. However, another option is preparation. There are some conditions where if you know that a baby is going to be born with certain conditions, you can prepare a surgical team and deliver the baby by a caesarean section so that you know when the delivery will take place. Take the baby immediately to surgery. And for many kinds of surgeries, the sooner that can be done on the baby the better, and the better the healing will take place subsequently. There’s also a possibility of correction and that might mean operating on the baby while it’s still in the uterus. That in itself is a challenging and dangerous thing to do, and therefore, only the most severe conditions are being explored for this.

    02:39 Neural tube defects would be an example. If it was possible to repair the neural tube defect before the baby was born, healing would be much better, and therefore, this is an area that might be explored further in the future. There’s also a possibility of selection.

    02:54 Through in vitro fertilization, you can fertilize the egg in a dish, and then you can assay for some genetic conditions and select the pre-embryos that are going to be returned to the uterus. And that’s already taking place. But finally, what I’d like to name is acceptance. In some cases, the developmental disability is a problem for others that they respond badly to it and that more sympathy and understanding of the nature of developmental defects might make things better for the individuals who have them. Another thing that we could do is to make sure that we test drugs for teratogenicity for the possibility that they might cause abnormalities before they’re released to the general population. And that’s generally done through animal testing. Preimplantation diagnosis, genetic testing, and selection are going to be a factor. Genetic counseling, if you can identify people with an inappropriate combination of genes, it’s possible to advice them in advance that this is the case.

    04:02 But I think probably the most significant one is good maternal nutrition, making sure that the mother avoids things which might cause harm during the course of development.

    04:11 And as I said, poverty and deprivation seem to be key factors in that kind of process.

    04:19 So then, what can we summarize from this particular lecture? We’ve looked at the three main stages of development, the pre-embryo, the embryo, and the fetus. We’ve identified the embryonic period from two and a half weeks after fertilization to the end of the eighth-week after fertilization as that is the sensitive period where major abnormalities of body systems are detectable. We’ve looked at the causes which might underlie that, realizing and accepting that we still have very much to learn in this area. And then we’ve looked at the implications for parents, children, and medical practitioners of knowing that a developmental abnormality is present in a developing baby. Thank you very much.

    About the Lecture

    The lecture Role of Prenatal Diagnosis – Weeks 3-8 of Embryogenesis by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Role of Prenatal Diagnosis – Weeks 3-8 of Embryogenesis

     John McLachlan, PhD

    John McLachlan, PhD

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