Lecture 12: Normal pregnancy

Question 1

What are the structural changes in the placenta that occur through early pregnancy, 2nd, 3rd trimester

Answer 1

1. Early pregnancy: stroma of villi becomes more cellular and vascularised

2nd trim: villous cytotrophoblast thins down to decrease barrier for nutrient exchange

3rd trim: villous cytotrophoblast is sparse

Overall there is increase in branching and size of the placenta

Question 2

What are the placental adaptions that help to increase transport of gas and nutrients as baby& placenta gets bigger

Answer 2

1. Villous structure is tortuous with a large SA against maternal blood lake
2. Syncitiotrophoblast on top of everything has microvillous surface for increased SA for transport
   1&2 also help with slowing down maternal blood flow to help transport
3. 3rd trim: most villi are small tertiary villi and the fetal capillaries are closely apposed to the syncitiotrophoblast so short distance to intervillous space with maternal blood

Question 3

What are the 3 parts of the maternal decidua that contribute to the placenta - how does this change as pregnancy progresses

What does decidua contribute to the baby

Answer 3

Decidual reaction is enhanced upon implantation: swollen stroma + glycogen stores

1. Decidua basalis underlies the implantation site and has transformed spiral arteries- remains attached to the placenta
2. Decidua capsularis overlies the embryo
3. Decidua peritalis: remaining decidua in the walls of the uterus.

As gestation goes on the embryo/fetus and amniotic cavity enlarges obliterating the uterine cavity, and the decidua capsularis fuses with the peritalis and are attached to the amnion + chorion laeve

Question 4

Is the decidua necessary for human implantation/pregnancy

Answer 4

No- ectopic implantation into abdominal cavity has gone to term live birth.

Question 5

What are the two placental membranes - not decidua

Answer 5

Amnion: avascular membrane closest to fetus that covers the cord and placenta. contains amniotic fluid

Chorion: contains fetal vessels - outside of amnion

Question 6

What are the contents of the umbilical cord/ structure

Answer 6

Network of myofibroblasts with spaces filled with mucopolysaccharides = Whartons jelly which help to provide turgor to the cord, keeping bv open

2 smaller arteries - deoxygenated
1 big vein - oxygenated blood

Question 7

What is the difference between true and false knot in the umbilical cord

Answer 7

False knots are alg- bulging of the bv known as varicosities

True knots are physically tied umbilical cord by movement of the fetus, if wharton jelly is ok then bv are still open but deficiency in jelly can lead to still birth

Question 8

What are the 5 major functions of Amniotic fluid

Answer 8

1. buoyant medium which allows symmetric growth
2. cushions the embryo/fetus
3. prevents adhesions of the fetus with membranes
4. allows fetus to move- prevent muscle atrophy
5. development of GI/respiratory tract function through practice of breathing and swallowing

Question 9

How does amniotic fluid change in volume and source initially and then closer to term

Answer 9

Goes from 10ml to peak 1000ml at 35 wks, 800 ml at term - continues decreasing

Source: initially ultrafiltrate of maternal plasma but 20+ weeks fetal urine is the major fetal contribution

Question 10

Where does the amniotic fluid flow through while it is getting recycled to match the fetal urine output of 500-1200 ml/day

Answer 10

1. Mainly fetal swallowing
2. Before 24 wks keratinisation of skin it can move across the skin
3. Diffusion back to the fetus through diffusion into fetal vessels of placenta and umbilical cord
4. Small amount of diffusion into maternal circulation

Question 11

What is polyhydramnios vs oligohydramnios

Answer 11

Poly: excessive amniotic fluid due to loss of swallowing- common in diabetic preg

Oligo: lack of amniotic fluid potentially due to kidney problems

Question 12

What infections can cross the placenta

Answer 12

HIV, CytoMegaloVirus- (CNS damage)
Small pox and other related viruses
Rubella
Toxoplasmosis from cat poo and raw meat.

Question 13

What infections cannot cross the placenta (usually)

Answer 13

HepB
Rabies
Measles
Malaria - but it is able to block up the intervillous space by causing macrophage infiltration which isn’t good

Question 14

What types of drugs can cross the placenta to cause harmful effects and when is this effect most prominent

Answer 14

Most damage done during the organogenesis period 20-70 days after the first day of LMP- up to one week before missing the next period so might not know if pregnant.

1. Thalidomide- anti inflammatory/angiogenic: limb reduction defects
2. Diethylstilbestrol: causes clear cell adenocarcinoma in vagina or cervix of adults
3. Ethanol: causes fetal alcohol syndrome, increases risk of still birth
4. Recreational drugs + smoking may cause intrauterine growth restriction and developmental delay
5. Warfarin causes fetal malformation so must switch to Heparin which doesn’t cross placenta

Question 15

What are 3 drugs safe to give to pregnant women

Answer 15

• Aspirin,
• Paracetamol- crosses placenta but safe
• Betamethasone: glucocorticoid given to prevent respiratory distress syndrome- accelerate lung maturity

Question 16

What does Estrogen priming of Progesterone mean?

Where is progesterone made mainly in pregnancy and why is that important

Answer 16

E2 upregulates P2 receptor.
P2 maintains the uterine quiescence and promotes development of the decidua. It also down regulates E2 receptors

P2 made by the syncytiotrophoblast of the placenta after 8 weeks so you don’t need the ovaries after that time and can have them removed if you have ovarian cancer

Question 17

What are the changes in the cervix for pregnancy

Answer 17

1. It softens and glands proliferate to occupy 1/2 mass of cervix
2. Mucus plug is secreted into the now honeycomb structure of the cervix -> delivered prior to fetus as the show
3. Up to 80% of non pregnant cervix is collagen

Question 18

What type of skin pigmentation changes are there in pregnancy and why does this happen

Answer 18

• darker nipples and areola
• development of the linea nigra - dark midline
• Chloasma - pigmentation on the face or neck which usually regresses after pregnancy

This is due to increased secretion of melanocyte stimulating hormone which is markedly elevated from the second month of pregnancy

Question 19

What are the changes to the abdominal wall and hair due to pregnancy

Answer 19

• In latter part of pregnancy, 50% of women develop Striae Gravidarum: reddish slightly depressed streaks in the skin of abdomen, thighs and breast
• Hair loss is reduced in pregnancy but the excess lost in puerperium