Physiology of Pregnancy Flashcards
Pregnancy stages
•Average Human Pregnancy – 40 weeks (9-months)
•Three trimesters - first (<12 weeks), second (12 weeks to
end week 26), third (27 weeks – birth)
-The first trimester is when the development of the fetus takes place and the fetus is more likely to be affected by external factors. eg alcohol or drugs or genetic mutations.
•Many physiological changes – ie. not pathological changes - that take place to support the to support the needs of a growing fetus
1•Supplying a baby with enough nutrients (O2, glucose, amino acids) for growth, development, production of amniotic fluid
2•Managing increased waste production – eg. CO2, nitrogen compounds
3•Change in hormones to support pregnancy and prepare
for delivery by both the mother and the placenta.
4•Anatomical changes to accommodate the growing fetus and
preparing for labour
5•Manage the stresses of delivery and potential haemorrhage
6•Postnatal Recovery and Breastfeeding
Systems that undergo some form of change during pregnancy.
•ALL OF THEM
- Endocrine
- Cardiovascular
- Respiratory
- Haematological
- Musculoskeletal / dermatological
Endocrine Change in pregnancy
3 MAIN HORMONES INVOLVED IN PREGNANCY that you need to know about;
1•BHCG ( Beta HCG)– dramatic rise in the first days-weeks - released from the corpus luteum initially, then by placenta.
The corpus luteum is a cyst on the ovary which is produced during ovulation, the corpus luteum releases BHCG and the point of this is to support the corpus luteum to secrete more progesterogene. As the pregnancy progresses HCG levels can fall as the progesterone level progress to be secreted from the placenta so there is less need for the corpus luteum to be present.
It is the hormone of pregnancy. The peak level of HCG is around 8-10wks and then drops as shown in the graph.
HCG = Human Choronion gonadotropin
2•Pro-gest-erone eg.pro-gestation - keeps the state of quiescence. it is a hormone of pregnancy. it does this by helping with the implantation of the embryo and maintaining the lining of the womb for implantation and ongoing through the pregnancy, it works by reducing the contractability of the. uterus and keeping it as stable as possible and in doing this it also acts on all other smooth muscle as well. i. e it can affect the bowel, ligaments because it is making everything as relaxed as possible.
3•Oestrogen – breast growth, areolar enlargement
it is a growth hormone of pregnancy.
progesterone and estrogen will continue to. rise throughout the pregnancy but progesterone will start to drop towards the end of the pregnancy to increase the intractability of the uterus towards birth time.
Other hormonal change –
Relaxin
Inhibin
TSH
The Placenta as an Endocrine Organ
•Placenta Produces Protein hormones:
1 •hCG (human chorionic gonadotrophin) – produced by trophoblast, first detectable 8-9 days, peaks 8-9 weeks.
2 •hPL (human placental lactogen) - Similar structure to prolactin and growth hormone. Larger placenta produces more hPL. Alters maternal carbohydrate and lipid metabolism to provide steady state of glucose for fetal requirements.
3 •hPG (human placental gonadotrophin) induces maternal insulin resistance to regulate fetal growth – this may become a pathological process seen as Gestational Diabetes.
4 •CRH (corticotropin releasing hormone)
- Steroids:
- Progesterone
- Oestrogen (oestriol)
Hcg
maintains corpus luteum secretion of prog & oest, decreases as the placental production of progesterone increases.
•beta unit forms the basis of pregnancy testing.
•Alpha unit can mimic LH, FSH, and TSH
- Large quantities are released in molar pregnancy and multiple pregnancy (eg twins)
- High levels cause vomiting (hyperemesis)
Progesterone
relaxes smooth muscle – everywhere!
- Maintains uterine quiescence by decreasing uterine electrical activity and keep the uterus nice and quiet.
- side effect is then Constipation, gastric reflux, supra-pubic dysfunction (the ligaments become very stretchy and the pubic symphysis becomes a little disjointed and can be uncomfortable and make some women require crutches to walk and some are confined to a wheelchair). ALL of these go back to normal after pregnancy.
- Progesterone acts as an Immune suppressor ( HLA ) and reduces the risk of the woman’s body reacting to the foreign body of the fetus. It is fundamental in helping the baby to tolerate the fetus.
- Lobulo-alveolar development in breasts
- Substrate for fetal adrenal corticoid synthesis eg cortisol
Oestrogen
- Growth of the uterus, cervical changes
- Development of ductal system of breasts
- Stimulation of prolactin synthesis
Haematological System
•40% increase in plasma volume - 2.5L to 3.7L (8-10kg fluid weight gain)
•25% increase in RBC only
- Leads to dilutional anaemia
- Plasma colloid osmotic pressure falls – shift of fluid out of the blood vessels and into the extracellular space. see in women as Oedema.
•Increase clotting factors – hypercoaguable state. The body increases its clotting factor so that at the time of delivery, there is less risk of bleeding. However, in doing so, this puts the woman at high risk of venous thrombosis. we assess women for venous thrombosis and put them on anticoagulants as required.
- Evolutionary balance between thrombosis and haemorrhage
- Increase plasma fibrinogen (increased ESR), platelets, factor VIII & von willebrand factor
Cardiovascular System changes in pregnancy
•Increased blood volume has implications on:
1• cardiac output (increased) as the heart is working much harder to push the large volume of blood around the body.
2• peripheral resistance (decreased), this is to keep the blood pressure low.
3• blood pressure is normally slightly lower.
•Heart is working hard to reach supply demands of the fetus – There is an increase in heart rate and stroke volume to account for an increase in cardiac output. some women may experience increased HR as palpitations.
•Remember C.O. = Stroke volume x Heart Rate
•Heart enlarges by 12% which allows for an increased venous return
•Innocent systolic murmurs are common (~90%)
•Beware diastolic murmur – may signify cardiomyopathy
Blood changes in pregnancy
Peripheral Vascular Resistance
•Peripheral vasodilatation (effect of progesterone)
•Peripheral resistance decreases by 35%
- Combined with increased cardiac output, results in slightly lower BP
- Decreased vascular resistance leads to lower blood pressure
Summary slide
Respiratory System changes in pregnancy
There is a growing fetus leading to an increased oxygen demand on the body and also an increase to shift CO2 out of the body.
what we really need to do is increase the rate of ventilation occurring within the lungs and increase the amount of oxygen crossing over into the fetus.
In pregnancy, you get a very raised intraabdominal pressure which is the feeling of fullness as the pregnancy grows and what happens is that there is a rise in the intraabdominal pressure and this can lead to splinting of the diaphragm.
This causes more diaphragmatic breathing and puts the body into a slight hyperventilation state.
- What changed in order to facilitate the splinting of the diaphragm is that the ribcage at the base actually starts to widen and this internalise the lung expansion to remain about the same so we are loosing any tidal volume due to splinting.
- The resting position of the diaphragm moves upwards and this in turn results in a slightly lower residual volume/capacity ( volume of air remaining in the lungs after maximum forceful expiration) but with the increased rib cage dimensions, we see that there is not a huge change in the total lung capacity and Inspiratory or vital capacity (The maximum volume of air that can be inspired after reaching the end of a normal, quiet expiration) remains the same but the tidal volume increases. This in. turn can lead to an increase in ventilation.
But The breathing frequency in pregnancy remains the same although women often complain of SOB, this is because of the widening of the rib cage and they are having to take much deeper breaths to get the air right into the lower lungs.
Lung Volumes; PREGNANT VS NON-PREGNANT
Increased rib cage dimensions which allow for an increase in tidal volume and increase in inspiratory reserve volume.
Because of the increase in CO and blood volume, there is increase in blood flow into the lungs when this is matched by an increase in today volume, you get more oxygen into the blood with every breath and with every pump.
This oxygenated blood is pushed around the body and as it reaches the baby, because of the difference in fetal HB, the babies HB has a higher affinity for O2 and so that oxygen that then crosses over from maternal blood into the fetal is more oxygenated.
Musculo-skeletal / Dermatological changes that occur during pregnancy
- Increased lumbar lordosis
- Ligamentous laxity (lack of strictness) caused by the increase in progesterone– pelvic girdle pain / pubis dysfunction (SPD). You can refer these women to physio or get them to do exercises or wear a belt that can hold the pelvis in position. having pubis dysfunction doesn’t affect the ability to labour in fact it might make it easier.
-If a woman’s pubis is very unstable, there is a risk that if you move the leg too high or manipulate the woman badly, you could dislocate the hip.
- Stretch marks (skin) due to collagen and high levels of pregesterone
- Changes in skin pigmentation - Linea Nigra in women who have darker skin already or people with pale skin, it is usually caused by high hormones of pregnancy. you can have melasma (s a tan or dark skin discoloration of the face), darkened nipples.
- Carpal Tunnel due to peripheral oedema
- Sciatica ( symptoms of pain, numbness, and/or weakness that radiate along the sciatic nerve from the lower back to the buttocks and leg)
- Cramps (can be a sign of anaemia)
Summary diagram
