S4: Maternal Changes in Pregnancy

Question 1

What are the three main causative factors in the changes of multiple systems during pregnancy?

Answer 1

1. The high levels of steroids (high oestrogen and progesterone).
2. Mechanical displacement (huge mass in abdomen).
3. The requirements of the foetus.

Question 2

Why can diagnosing abnormalities in pregnancy difficult?

Answer 2

• Pregnancy is a physiological event and the body has to adapt. These systems usually return to normal very quickly after delivery but not always.
• Thus to diagnose abnormalities in pregnancy is difficult because there are so many changes going on that are normal, thus to diagnose the abnormalities you need to detect changes in the normal changes.
• Pregnancy changes may also exacerbate a pre-existing condition e.g. hypertension that previously hadn’t been recognised.
• Pregnancy can also uncover hidden or mild conditions such as diabetes.

Question 3

What events may the changes in pregnancy try and help with?

Answer 3

• An increased size of the uterus.
• Increased metabolic requirements of the uterus.
• Structural and metabolic requirements of the foetus.
• Removal of foetal waste products.
• The production of amniotic fluid.
• Preparation for delivery and puerperium (6wk period after pregnancy where things go back to normal).

Question 4

List some systems that changes during pregnancy occur in

Answer 4

• Energy balance.
• Respiratory system.
• Cardiovascular system.
• Gastrointestinal system.
• Urinary system.
• Endocrine system.

Question 5

What hormones causes most of the pregnancy changes?

Answer 5

~Placental peptides~:
hCG released first and hPL (human placental lactogen) also released. hPL causes woman to become hypertensive and increases glucose in the blood (is anti-insulin). It is similar to GH.
~Maternal Steroids~:
After about week 7 of pregnancy, the corpus luteum dies as it is no longer required and placenta takes over maternal steroid (progesterone, oestrogen) production and releases in high amounts.
~Placental and foetal steroids~:
Mainly progesterone and oestrogen as mentioned (there are different types of oestrogen, oestradiol and oestriol both released).
~Maternal and foetal pituitary hormones~:
GH released and increase in thyroid hormone production (increasing metabolic rate). Production of prolactin (will allow lactation after delivery) and CRF (corticotropin releasing factor) released from hypothalamus.

Question 6

What are the effects of high placental steroids?

Answer 6

ts effects can be explained because the high steroids can act on different receptors other than their own. This is why they can affect multiple systems.
- Affect the RAAS system (thus blood pressure).
- Affect respiratory centre.
- GI tract.
- Blood vessels (cause massive vasodilation).
- Uterine myometrial contractility.

Question 7

Describe the total weight gain in pregnancy

Answer 7

From pre-pregnancy weight to the point at which you reach full term, the average woman would have to put on roughly 12.5-12 kg. Ideally keep to less than 13Kg, so failure to gain or sudden change may need to be monitored. But we don’t really do this clinically as investigating it isn’t particularly helpful in any way.

• Foetus plus placenta = 5kg.
• Fat and protein stores = 4.5 kg.
• Body water increased in all compartments = 1.5 kg.
• Breast tissue growth = 1kg.
• Uterus = 0.5-1kg.

Question 8

Why do energy levels nned to increase during pregnancy?

Answer 8

• We have increased output of energy through the increased respiration and cardiac output that is using up more energy.
• Need to store energy for the foetus to utilise and also for labour and puerperium (as this takes a lot of energy so women who are underweight struggle). We gain about 4-5Kg in fat and protein that is laid down as stores in the anterior abdominal wall. This store is really important for use later in pregnancy and afterwards.
• The pregnant woman’s basal metabolic rate increases by about 350kcal/day (increases by 350kcal per day) during mid-gestation.
  It increases by about 250kcal/day by late gestation. Most is required for the foetus and uterus, about 25% is for respiration.

Question 9

How does glucose levels change in pregnancy?

Answer 9

The pregnant woman needs increased glucose levels in her blood in the 2nd trimester and the glucose is transported across the placenta via facilitated diffusion to the baby. The baby will only function well with glucose! The foetus does also store some glucose in their liver. To supply constant stream of glucose to the baby across the placenta, the mother becomes insulin resistant due to hPL.

Question 10

Describe changes in glucose in the first trimester of pregnancy - maternal reserves

Answer 10

In the 1st trimester, the pancreatic beta cells increase in number in response to slight insulin resistance. Plasma insulin increases and therefore more glucose is laid down as stores (glycogen or converted to fatty stores) and or used by muscle.
This is to build up the maternal glucose reserves, as a result we see that fasting serum glucose decreases during this period is low.

Question 11

Describe changes in glucose in the second trimester of pregnancy - foetal reserves

Answer 11

In the 2nd trimester, the hPL and steroid levels are higher causing increased high insulin resistance. As a result insulin cannot fight back against this level of resistance and we see less glucose entering into stores. Instead serum glucose increases and this increases the concentration gradient at the placenta. Therefore more glucoses crosses the placenta to the foetus. This insulin resistance is not diabetes and is normal. However if the woman has a history of diabetes in her family, is overweight or has bad genes this may push her over the edge and she becomes diabetic (gestational diabetes).

Question 12

Describe total water gain during pregnancy

Answer 12

• In the pregnant women, there is a big increase in total body water and the volume in all of the women’s compartments will increase. The women will have about 8.5L.
• This is due to the high E2 oestradiol) and progesterone acting on the RAAS system. They act in a mineralocorticoid manner.
• They increase retention of Na+ in the kidney therefore water moves along with it and there is increased water retention increasing plasma volume (by about 40-50%). They can also reset the osmostat in the brain and lower the thirst threshold.
• This extra water will be distributed in the plasma and some will go to the foetus, some to placenta and amniotic fluid.
• Also can be seen in uterus and mammary gland. It also causes oedema in the ankles (due to extra fluid and reduced venous return due to mass in chest impeding venous return) and it can occur in the lungs which is dangerous.

Question 13

Describe how respiration and O2 consumption changes during pregnancy

Answer 13

• Oestrogen and progesterone affect the way the pregnant women breathes.
• There is increased sensitivity of the respiratory centre to CO2 and this causes them to breathe more deeply (not more frequently and should not be tachypneuic). As a result, her minute volume will increase by 40%. Therefore a blood gas would show that arterial PO2 is high but PCO2 is low.
• This is useful as it helps facilitate placental gas transfer. The high PO2 in maternal blood causes a steep gradient for oxygen to diffuse into foetal blood where O2 is lower. The low PCO2 in maternal blood causes a gradient for the high levels of CO2 in the foetal blood to move out into maternal blood and be breathed out.
• There is some contribution to increase breathing due to the thoracic cavity being different (ribcage displaced upwards and ribs flare outwards) but this is more minimal.

Question 14

Describe changes in maternal blood during pregnancy

Answer 14

• Mothers plasma volume increases by about 45 %. The more babies you will carry, the more it will increase.
• Red cell mass also increases and more erythrocytes are made.
• However if you checked haemoglobin concentration of a pregnant woman it would have gone down, because although red cell mass has increased, the volume of plasma has increased by a huge amount. This is haemodilution and looks like apparent anaemia as the concentration of Hb is lower, but it ISN’T anaemia it is physiological. Anaemia is not physiological.
• The maternal gut is also more efficient at absorbing iron in iron in order to enable this increased red cell mass.
• There is also an increase in leucocytes and clotting factors. The blood actually becomes hypercoagulable, this is due to increased fibrinogen for placental separation but there is an increased risk of thrombosis! So pregnant woman is at increased risk of DVT.

Question 15

Describe foetal blood and its difference to adult

Answer 15

Foetal Hb is different to adult Hb. Foetal Hb is shifted to the left and has a very high affinity for oxygen. This is really helpful as you have both the concentration gradient of O2 and the high affinity of foetal Hb to allow O2 to pass nicely through the placenta (as foetal Hb has higher affinity than adult).

Question 16

Why is smoking dangerous in pregnancy?

Answer 16

Smoking is dangerous in pregnancy as it increases carboxy-Hb in the mothers blood, this is more permanent and reduces the amount of oxygen the foetus can get hold of (as less in maternal blood). This leads to foetal hypoxia.

Question 17

Describe changes to the heart (CVS system) during pregnancy

Answer 17

• Pregnancy is characterised by a high volume low pressure system. We see changes in the ECG and hear heart sounds. The uterus expanding contributes to this.
• There is also increased cardiac output (HR x SV), this is due to the increased blood volume and SV has increased quite a lot (HR doesn’t increase that much).
  This increased CO begins as early as 3 weeks and is at maximum of 40% increase at 28 weeks. This is required for the maternal muscle and to provide the fetal supply.
• Underlying cardiac disease can become apparent and exacerbated at pregnancy causing serious problems! This tends to occur in older women who have a worse heart and circulation.

Question 18

Describe changes to the blood vessels (CVS system) during pregnancy

Answer 18

• If our CO increases then naturally we would expect blood pressure to increase, but it doesn’t! Instead blood pressure actually decreases, this is due to reduced peripheral resistance due to great vasodilation by progesterone. This allows increased flow to the uterus, placenta, muscle, kidney and skin
• In pre-eclampsia, there is no relaxation of the vascular smooth muscle.
• We also see neoangiogenesis (growth of extra capillaries in the skin, spider naevi), this helps assist in heat loss.

Question 19

Describe gastrointestinal tract changes during pregnancy

Answer 19

• The high steroids (progesterone, oestrogen) cause an increase in appetite and thirst. The progesterone also causes generalised smooth muscle relaxation, this in the blood vessels causes vasodilation and lower BP.
• However in the gut, progesterone causes the smooth muscle of the gut to relax resulting in reduced GIT motility this leads to constipation. There is also relaxation of the lower oesophageal sphincter, this leads to reflux of stomach contents up the oesophagus causing heart burn. The large uterus can also push up and cause acid reflux. 80-90% of pregnant women will get heartburn.
• Having small frequent meals can help prevent this. We can also use alginates like Gaviscon.

Question 20

Why is dietary supplementation of folic acid important in pregnancy?

Answer 20

• Folic acid is really important for many bodily functions. It is involved in DNA production, growth, blood cell production etc. As one can imagine a pregnant woman will be doing much more of all this stuff, her uterus, the placenta and the foetus all require it. Thus for anyone who woman who wishes to get pregnant it is advised to take folate supplementation 3 months before getting pregnant! The supplementation is advised 400 micrograms/day up to week 12. Deficiency of folate in the mother is linked to spina bifida (a neural tube defect). You want to take it BEFORE you get pregnant.

Question 21

Describe urinary system changes during pregnancy

Answer 21

• Due to progesterone, our urinary tract (ureters, bladder) dilates and relaxes so it becomes more floppy. This gives increased risk of UTI due to stasis in their system (like how in men with BPH, prostate obstructs urethra causing stasis and UTI).
• The kidney is also affected, due to vasodilation of the vessels, more blood flows into the glomerulus and there is increased filtration. Thus the pregnant woman urinates a lot more. Renal function is also often checked, creatinine, urea and uric acid concentrations in blood (and hence urine) should be lower (as haemodilution) because the pregnant lady is peeing more. A pregnant lady with high levels of these may be suffering from renal impairment!
• It’s not only increased filtration however that causes increased urination, it is also caused by the enlarged uterus compressing the bladder.
  This leads to increased frequency of urination during the first trimester!
• During second trimester the uterus lifts out of the pelvis and there is some relief as less compression of the bladder.
• However in the third trimester, the baby’s head descends down onto the bladder compressing it, that again increases frequency of urination.

Question 22

Describe changes in uterine size during pregnancy

Answer 22

• The non-pregnant uterus is quite small with a small volume. However by term, the uterus has increased massively in size. This is mainly due to the effect of oestrogen on the myometrium, causing growth of existing muscle fibres (hypertrophy). The fibres are arranged in such a manner that is in a spiral shape that will help push the baby out the uterus. There is also a big increase in blood flow to the uterus.
• The lower aspect of the corpus and upper aspect of the cervix makes up the lower segment. This is what is cut in a lower segment cesarean section as it is more fibrous and bleeds less.

Question 23

Describe changes in cervix size during pregnancy

Answer 23

• The cervix’s primary function during pregnancy is to keep the baby in the uterus and retain the pregnancy. During pregnancy we therefore want a nice closed cervix and a myometrium that is quiescent and doesn’t contract. In pregnancy there is an increase in vascularity of the cervix, it becomes softer but it still fibrous due to the high collagen (turns bluer, change in connective tissue).
• There is also proliferation of the glands of the cervix, there is high production of mucus producing a mucosal plug. This is a great protective barrier against infection, we don’t want pathogens moving up the vagina into the uterus.
• However during labour, we want a myometrium that is contracting pushing the baby down and a cervix that goes from closed to opened up nicely. When labour starts prostaglandins will cause breakdown of collagen/connective tissue making the cervix soft and squishy so the baby and slide through (we can even induce labour by injecting prostaglandins into the cervix).

Question 24

Describe the return to normal of physiological changes after labour

Answer 24

• As soon as the placenta has been delivered, there is a sudden and rapid fall in steroids because the placenta is gone! This results in reversal of the physiological changes that had been undergone during the pregnancy. By six weeks the woman will be back to normal. This demonstrates that most of the endocrine driven changes return to normal quickly.
• The uterine muscle rapidly loses oedema but contracts slowly. However it never returns to pre-pregnancy size.
• As the steroids continue to fall, it permits the action of prolactin on breast to allow lactation. The breast has been prepared by oestrogen throughout the pregnancy so is ready for breast-feeding.