ART-today and future possibilities Flashcards
define infertility
Infertility defined as the failure to conceive after 1 year of regular unprotected intercourse.
what are the main causes of infertility (that occur in 1/7 couples in the UK)
- Mechanical blockage to egg and sperm meeting:
o Infection/occlusion of vas deferens or uterine tubes e.g. endometriosis and chlamydia. Cells from endometrium implant on other parts of the pelvis while still responding to hormones thus allowing shed and causing bleeding into pelvis. This can block uterine tube causing inflammation affecting fertilisation.
o Previous ligation for sterilisation.
o Endometriosis – endometrial cells escape and still continue to respond to hormones.
o Congenital defects. - Failure of gamete production or release:
o Anovulation, maternal age (decline in number of eggs and quality as they’ve remained arrested on the spindles for a long time), PCOS.
o Azoospermia (no sperm), asthenozoospermia (reduced motility), teratozoospermia (abnormal morphology). - Failure of fertilisation/implantation & miscarriage:
o Genetic factors.
o Endometrial receptivity, maternal age. - Idiopathic – 40% of cases.
describe assisted reproductive techniques (ART)
- Inducing ovulation with exogenous hormones if mother is anovulatory.
- By-passing the uterine tube (IVF).
- Direct collection of sperm from the testis/epididymis if there’s absence of the vas deferens or problems with ejaculation.
- Direct insertion of the sperm into the egg (ICSI) if they’re not swimming. This is because they are only swimming once mixed with secretions from the prostate etc.
- Donor gametes (egg + sperm).
- Combination of the above.
how can ovulation be induced
with gonadotrophins or by removing negative feedback
describe how ovulation can be induced with gonadotrophins
• Used to treat women who are anovulatory or who have oligo/amenorrhoea.
• Gonadotrophins in these women usually normal or slightly elevated: usually polycystic ovary syndrome.
• Aim is to induce single dominant follicle.
• Daily injections of (mainly) FSH and LH to stimulate the ovaries more oestrogen production induce ovulation.
o Monitor by ultrasound during the cycle, to ensure ovaries are not being hyper-stimulated.
o To kick-start a cycle exogenous gonadotrophins like FSH and LH stimulate ovaries for follicle growth, which then grows, and make oestrogen to send feedback.
o Recombinant FSH is made with human DNA and yeast/bacteria of urine of menopausal women as high gonadotrophin levels due to no feedback from oestrogen.
describe how ovulation can be induced by removing the negative feedback
• Used when gonadotrophin levels are normal, but not cyclical.
• At the end of the cycle, when the CL regresses, the negative feedback is removed due to the fall in progesterone and estradiol –> inter-cycle rise in FSH –> cohort of early antral follicles are recruited into the MC.
• We can ‘trick’ the pituitary into thinking there was a corpus luteum and it has regressed causing a decrease in sex steroids –> rise in FSH –> rise in oestrogen.
o There are follicles in the ovary making oestrogen, therefore, we can remove the negative feedback exerted by this.
o However, can’t reduce progesterone as there has not been a corpus luteum to make any.
what are the 2 ways to remove oestrogen feedback?
- Block the E2 receptor on the pituitary gonadotroph cells with a selective oestrogen receptor modulator (SERM) e.g. Clomiphene/Clomid
- Stop E2 production by using an aromatase inhibitor e.g. Letrozole.
describe IVF (in vitro fertilisation)
- Downregulate the HPG axis using GnRH analogues (commonly an antagonist).
- Stimulate ovaries by giving fsh–> when you have lots of follicles, they produce oestrogen–> stimulate ovulation by giving hCG trigger which mimics LH spike.
- Collect the oocytes (needle through vaginal wall (transvaginal) and pierce follicle to suck follicular fluid and take egg) and fertilise them in vitro.
- Culture the embryos for 3 – 5 days and transfer them back into the uterus.
- Confirm pregnancy.
- Luteal phase support e.g. cyclogest (progesterone).
As failure will occur at each stage, we require as many eggs as possible and so we hyper-stimulate the ovaries to increase follicle numbers.
what normally happens to growing follicles?
When the growing follicles acquire FSH receptors, they become responsive to FSH. This results in a cohort of early antral follicles being recruited into the MC.
As they start to develop due to the increase in FSH, they produce oestrogen–> negative feedback back to FSH.
This decrease in FSH leads to selection of the dominant follicle (one which has the greatest number of FSH receptors + most efficient downstream cascade). While the remainder of the follicles die as they lose their stimulant.
The dominant follicle also induces LH receptors on the GCs–> continues to become stimulated and produce oestrogen which thickens lining of uterus.
what happens when you give exogenous FSH injections?
When you give exogenous FSH injections, there’s no negative feedback as the HPG axis has been switched off using GnRH analogues (agonist or antagonist).
FSH levels remain high–> all the follicles survive and become dominant follicles.
= controlled ovarian stimulation.
why do we downregulate the HPG axis?
• The reason why we downregulate the HPG axis is because each dominant follicle will be producing lots of oestrogen and 2 days of sustained high levels of oestrogen will lead to an LH spike and subsequent ovulation. Therefore, the patient will try and ovulate all the dominant follicles. Therefore, pituitary is switched off to prevent the LH spike.
- We don’t want too many follicles as it can lead to ovarian hyperstimulation syndrome (OHSS). Ovulation is an inflammatory process. One of the mediators is VEGF, which leads to neo-angiogenesis + makes blood vessels permeable = people can die from pulmonary oedema.
- We ultrasound every day to count the number of follicles + adjust the daily dose accordingly to select a good number of follicles.
- Once there is a good number of follicles (12-19mm), a hCG injection is given, which mimics LH, therefore, it binds to the LHR.
- 34-38hours is allowed for the completion of meiosis 1 and initiation into meiosis 2, then the eggs are collected using transvaginal needle aspiration, under U/S guidance.
o NOTE: Collect before 40hours, as otherwise they will ovulate and its difficult to collect the eggs from the uterus.
describe sperm preparation for IVF or IUI (intrauterine insemination)
- Density centrifugation –> more dense at the bottom.
o Semen is layered on top of it –> centrifuge.
o Dead sperm have disrupted membranes –> less dense.
o + cellular debris are less dense than live sperm, so the live sperm collect at the bottom. - Once the sperm are prepared, IVF in a dish.
- Drops of media, each contain an egg, under a drop of mineral oil. Add sperm sample to each.
what is in vitro fertilisation?
- The sperm and the egg are incubated together at a ratio of about 75,000:1. Duration of this co-incubation traditionally 16-18 hours. Approximately 65% of the eggs will fertilize.
- The conditions of the incubator are highly controlled: nutrients, acidity, humidity, temperature, gas composition of air, and exposure to light.
describe the embryo culture
- The fertilized egg has 2 pronuclei. This is the first sign of fertilization.
- The developing embryo contains 6-8 cells 3 days after fertilization.
- Blastocyst 5 days old approximately 100 cells – this is the first differentiation event (inner cell mass is visible + surrounding cells are destined to become the placenta).
what is embryo transfer?
- Embryo transferred to the patient’s uterus through catheter, which goes through the vagina and cervix, usually under ultrasound guidance.
- Single embryo transfer to avoid multiple pregnancies, though 2 – 3 may be transferred in women over 40 or in women who have had repeated implantation failure.
