Pregnancy Flashcards
4 satges to foetal development
embryo
foetus
viability
term
Main maternal changes of pregnancy
Increased weight Increased hormone levels Increased clotting Decreased BP Increase in body temperature Increased breast size Increased vaginal mucus production Increased nausea and vomiting
when is start of pregnancy
first day of menstrual cycle that results in fertilisation
What happens to levels of hCG during pregnancy
increases during first trimester and peaks here but then declines rapidly at end of first tirmester
What happens to levels of placental lactogen during pregnancy
increase steadily whole way through
What happens to levels of progesterone during pregnancy
increase steadily whole way through
What happens to levels of oestrogens during pregnacny
increase steadily whole way through
What are increases in oestrogens, placental lactogens and progesterone paralelled with
Plaental size
What produces hCG
Placenta
What is the luteo-placental shift
Change from corpus luteum to placenta as main source of progesterone and oestrogens
When does placenta become main source of progesterone
10 weeks
What facilitates this luteo-placental shift
increase in size of placenta and from 6 weeks the corpus luteum gradually produces less progesterone despite the elevated levels of
whats special about fetal adrenal glands
well developed and large even in first trimester
What is involvement of fetal adrenals in production of circulating maternal oestrogens
Placenta lacks the enzyme that converts pregnenolone to androgens. The fetal adrenals are able to produce a weak androgen DHEA which is sulphated in the fetal liver to give DHEA-S
Significance of androgen produced by fetal
It is inactive so a female fetus isnt exposed to an androgen during development
What happens to DHEA-S after its sulphation in fetal liver
circulates to placenta where is converted to 17beta-oestradiol
Pathway leading to high levels of circulating maternal oestriol
DHEA-S is induced to be hydroxylated to form 16aOH-DHEA-S which is precursor for estriol. The precursor circulates to placenta where is converted to estriol
Reason for increased blood clotting tendency
thought to be protective against losing too much blood during delivery and to do with the interactions between maternal and foetal blood
Changes in maternal BP during pregnancy
BP decreases for first two trimesters and is lowest in second then increases during the third one
Cause for concern of lowered BP in pregnant women
Susceptible to fainting if stand for too long
Reason for increased size of breasts
Increased levels of prolcatin, oestrogens and placental lactogen
Reason though to behind altered appetite
Baby puts pressure on GI tract decreasing its distensibility so smaller meals more often are what is suggested
Reason for altered emotional state
Hormones
Altered joints during pregnancy
Connections between bones in pelvis become more flexible to permit growth of baby
2 reasons behind how there is no signs of rejection reaction despite a non self entity surviving in a woman for 9 months
Utero-placental interface produces numerous factors that modify mothers immune response
Placenta expresses bizarre HLA antigens- normaly HLA are very polymorphic with millions of variants however placenta HLA only has 5 variants. The structure of placental HLA is very simplistic giving message to maternal immune system that the tissue is human but not non-self which downregulates action of leukocytes
What controls development of the features
Genetic
Environmental factors such as maternal diet
Evidence for importance of genetic control
Any chromosome abnormalities show large changes in development
Only viable example of too few chromosomes
Turners syndrome- 45-X0
When is embryo most vulnerable to abnormalities
Early trimester
What is a teratogen
Agent that can hinder embryo development
Most dynamic part of human development
Embryology- first 8 weeks when go from single cell to something resembling a human
Define conceptus
Everything resulting from a fertilised egg
Define embryo
baby up to 8 weeks of development
Define fetus
Baby for the rest of pregnancy
Define infant
Applied after delivery
Where does embryo recieve nutrients in first week of development
Secretions of fallopian tube
Differing meaning of embryo
During this first week (PF), the whole conceptus is the embryo. After differentiation to form a blastocyst, the embryo refers to the cells that contribute to (or are) the baby alone; other tissues have separate identities
5 functions of placenta
Exchange of nutrietns and waste products Anchorage of conceptus to maternal decidua Separation between 2 tissues Biosynthesis Immunoregulation
Primary subunit of placenta and function
Placental villus- This provides a very large surface area (estimated to be 11 square metres) for exchange between the maternal and fetal vascular systems, thus meeting a primary requirement for exchange functions
Structure of placental villus
Within each villus there is a complex blood supply, including arterial and venous vessels, connected to smaller capillaries in the terminal portions of each villus. Note that the arterial system contains de-oxygenated blood, and the venous blood is oxygenated – because the placenta has a parallel function to the lungs for the fetus during pregnancy
What is placenta subdivided into
The maternal surface of a placenta is sub-divided into cotyledons (30-60 per placenta). Each cotyledon contains one or more villi, with larger cotyledons containing more villi
Describe development of placenta
9 days post fertilisation the conceptus is almost completely implanted within the maternal decidualising endometrium. At this stage of development, the outer layer of the conceptus are multinucleated syncytiotrophoblast, which contain fluid-filled lacunae. The underlying layer of cytotrophoblast is proliferating adjacent to the embryo: this is where the placenta will develop. Following implantation, the cytotrophoblast proliferate into the syncytium; first a columnar structure is formed (cytotrophoblast column), which then undergoes branching (villous sprouts). At the centre of each villus are mesenchymal (extra-embryonic mesoderm) cells, from which the villus vascular system develops. The branching process continues through out pregnancy, giving rise to the complex branched villi
Outer layer of conceptus at implantation stage
Syncytiotrophoblast
Second outer layer of conceptus at implantation stage
Cytotrophoblast
For how long is conceptus separated from maternal blood supply and how
As conceptus grows it does make transient contact with maternal capillaries however the rapidly proliferating cytotrophoblast cells form shell around the conceptus which completely isolates it by 4 weeks post fertilisation
Histotrophic nutrition
Nutrition to conceptus via endometrial glands
Haemotrophic nutrition
Nutrition to conceptus via maternal blood
Source of nutrition in first trimester of pregnancy
Histotrophic
How does change from histotrophic nutrion to haemotrophic nutrition occur
For first 8 weeks post fertilisation spiral arteries are blocked by cytotrophic plugs then for next 4 weeks these plugs begin to break down beginning with those nearest periphery
Arteries supplying placenta
spiral arteries
Cause of miscarriage late first trimester
If placenta is not fully anchored to maternal decidua then the increased pressure when it is exposed to maternal arterial supply can detach the placenta
Overall regulation of placental growth
In general terms, the placenta regulates its own growth and development through autocrine mechanisms. We know that it can produce a range of different growth factors and other proteins
Effect of maternal decidua on placental growth
The maternal decidua mainly seems to modulate (restrain) placental growth and development, so that the placenta is optimal for both the mother and the fetus
Maternal risks during pregnancy
Very rare during gestation but issues come from labour and delivery
How is blood loss minimised from severing on uterine spiral arteries
Contraction of the uterus after placenta has been delivered- sometimes drugs can be given for this
Important thing to check post delivery relating to placenta
If there are pieces missing
Problem of placental tissue being left behing
Placental tissue is very inflexible so prevents contraction of placenta and allows continued blood flow through spiral arteries
Main risk to conceptus during development
Chromosome aneuploidy
Breakdown of early delivery
About 10% of infants are delivered early; half of these result from the process of labour starting before term. The other half are from pregnancies with deteriorating maternal or fetal health, to the extent that delivery is the best option to save the life of the mother, or the fetus, or both. of them
Define stillbirth
Stillbirth refers to the death of an infant within the uterus, so that it is delivered without any signs of life. Precise definitions vary, and may include gestational age or fetal weight limits. Post 23 weeks (the viability limit) is often used
How to detect stillbirth
Monitor health of fetus using doppler and ultrasound
