pregnancy Flashcards
1st trimester
0-13 weeks (not clear pregnant)
2nd timester
13-26 weeks (clearly pregnant)
what happens at week 26 (2nd -> 3rd timester)
absolute limit viability
3rd trimester, and physical changes
26-39 weeks (very clearly pregnant, with abdomen large and angle of back posterior to compensate)
what happens between weeks 37-41
term
when do maternal and placental changes occur in pregnancy
maternal changes occur throughout, and placental changes are complex and occur mostly in first half (most risks during first trimester)
maternal changes: 1st term (and later)
altered brain function, altered hormones (mainly steroids), altered appetite (quantity and quality; GI imbalance causes hyperemesis gravidarum “morning sickness”), altered emotional state (unpredictable), altered immune system (to allow pregnancy to continue but still retain resistance to disease)
maternal changes: 2nd term (and later)
increased blood volume, increased blood clotting tendency, decreased blood pressure (unusual as normally increased blood clotting and increased blood pressure go together), altered fluid balance (kidneys in overdrive alongside increased blood volume)
maternal changes: 3rd term
increased weight, altered joints (become more flexible)
maternal endocrinology throughout pregnancy: HCG
rises during week after implantation occurs and rapidly peaks at week 9 during first trimester (measured in pregnancy test) to keep endometrium from shedding, before declining rapidly and plateauing low
maternal endocrinology throughout pregnancy: placental lactogen
slow increase from week 5 to term
maternal endocrinology throughout pregnancy: oestrogens
slow increase from week 5 to term
maternal endocrinology throughout pregnancy: progesterone
fast constant increase to term (100x more than body has previously dealt with)
relative risk to maternal health in early parts (1st and 2nd trimesters) of pregnancy
small
what is the main risk to maternal health or life linked to
delivery
fertilised egg size vs size of infant
<1mm -> 30cm
define conceptus
everything resulting from the fertilised egg (baby, placenta, fetal membranes, umbilical cord, amniotic fluid)
define embryo
baby before it is clearly human (e.g. 5-6 weeks with liver to make erythrocytes)
define foetus
baby for the rest of pregnancy (3 months)
define infant
less precise, normally applied after delivery
when do blastocysts exist, and what 2 layers of cells do they contain
before embryo (e.g. 9 days), containing epiblast and hypoblast
count for pregnany to ensure mother can roughly know how long
gestation age = first day of last menstrual period (as don’t know when ovulation occured, but usually approx. 14 days after)
describe Carnegie stages of human development
summary of developmental changes, with distinct changes in development to appear more human
significance of 2 week delay between ovulation and first day of last menstrual period
no huge difference at term, but viability is dramatically affected by gestational age
how to observe pregnancy
observe in utero or outside (e.g. ultrasound), and with measurements by circulating factors (e.g. in blood), or dimensions
what are used to study mechanisms of pregnancy
other animals (e.g. fish, chick, mouse) as similar structures develop similarly to humans, as gene families involved in development are similar
difficulty with using other animals to model human mechanism of pregnancy
different pregnancy lengths etc. (but also not just size dependent), so must be cautious
when is embryo/foetus most vulnerable to teratogen
during first 8 weeks as most rapidly developing, although brain vulnerable into second trimester also
what can mal-development help to identify
when conceptus is most vulnerable, and which structures are most vulnerable
describe foetal structure of placenta
disc (about 20cm diameter), with blood vessels and with thinner layer around called foetal layer which encloses amniotic fluid, and umbilical cord connecting to baby
describe maternal structure of placenta
made up of 30-60 components (cotyledons) which are main subdivisions, with gaps between them due to maternal tissue being left behind in uterus
describe basic placental structure of cotyledon
very branched structure (placental villus tree with many subdivisions for large surface area), with central stem through which blood vessels pass, where communication of materials between maternal and foetal blood supplies occur (both circulations don’t come into contact with each other, but oxygen and other nutrients exchanged from oxygenated maternal artery to deoxygenated foetal artery, before returning to foetal heart via foetal vein - similar to adult pulmonary system with respect to artery and vein oxygenation and deoxygenation)
4 key features of placenta
very branched square structure provides large surface area, very effective for transport of molecules, anchors baby securely for 9 months, intimate contact between maternal and placenta tissues (plays part in immunology)
5 functions of placenta (SEBIC)
separation (maternal and foetal blood systems), exchange (between blood systems), biosynthesis (very active, producing HCG, oestrogens, progesterone etc.), immunoregulation (unique with no variablity, as contains antigens to signal human, but not which human), connection (anchor)
how does placental villous tree develop
starts as single layer of cells in blastocyst -> proliferate and differentiate -> branches as iterative (repeating) process to become more complicated and have a larger surface area, becoming a “placental villous tree”
describe contact at 8 weeks gestation age to allow more growth of baby
spiral artery remodelling allows very large volumes of blood can access from maternal circulation to placenta during 2nd and 3rd trimesters, with cytotrophoblast shell limiting blood and oxygen supply to embryo during 1st trimester to prevent free oxygen radicals going into rapidly dividing cells
4 outcomes of placental mal-development
miscarriage (late 1st trimester), miscarriage (2nd trimester), pre-eclampsia (early delivery), foetal growth restriction (small infant)