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714 S P E C I A LT Y P R A C T I C E I N C R I T I C A L C A R E

renal complications of pregnancy and is associated with Hepatobiliary Changes in Pregnancy
the onset of preterm labour. 45
There is no significant increase in hepatic arterial blood
The kidneys receive a proportion of the additional cardiac flow during pregnancy, despite the 40–50% increased
51
output resulting in a 30% increase in renal blood flow. cardiac output. There is, however, a doubling of blood-
51
The glomerular filtration rate (GFR) increases 40–50% flow to the liver supplied by the portal vein, which may
during the first trimester and then reduces slightly towards have an impact on oral medication metabolism in the
18
the end of the third trimester. The increase in GFR may liver. There are also changes in other hepatic enzymes
result in the tubule active transport systems for both responsible for drug metabolism, resulting in a change
glucose and proteins to be exhausted, with both glycos- in pharmacokinetics of some medications, e.g. higher
uria and proteinuria common in pregnancy. Glycosuria plasma levels of midazolam. Serum albumin levels
is not related to blood sugar levels and is unhelpful in reduce to 30–40 g/L for the majority of pregnancy, with
monitoring diabetes. Proteinuria, up to 300 mg per 24 levels as low as 25 g/L normal during the second post-
46
hours, is considered normal in pregnancy. Conversely, the partum week. This low albumin level reduces colloid
high GFR results in lowered serum levels of both urea and osmotic pressure that contributes to the dependent
creatinine. A plasma urea level exceeding 4.5 mmol/L oedema, for example swollen ankles, that is common in
and plasma creatinine level higher than 75 µmol/L, pregnancy.
should be viewed as abnormal and indicative of potential The general smooth muscle vasodilatation affects the
renal impairment. 18,46 There is conflicting information hepatobiliary ducts, resulting in sluggish bile motility
regarding normal urine output during pregnancy, with and delayed emptying of the gall bladder. These changes
some studies suggesting no difference to that during non- lead to an increased incidence of cholelithiasis and cho-
pregnancy and others reporting an increase in 24-hour lecystitis during pregnancy.
urine volume after 12 weeks’ gestation. 45,47

Postpartum Renal Changes HAEMOSTASIS SYSTEM
The most significant renal change is the diuresis that During pregnancy, the woman’s body prepares for the
occurs in the 1–3 days postpartum. This diuresis serves separation of the placenta, a time of potential large blood
to offload the additional blood volume that the woman loss. The blood flow to the placental bed at term is in the
has had circulating for the duration of the pregnancy. range of 600–800 mL/min. Both elements of the haemo-
There has been little examination of ‘normal urine output’ stasis system are activated during pregnancy (coagulation
with the standard 0.5 mL/kg/hr reported as a minimum and fibrinolysis), with pregnancy and particularly the
acceptable level, however a true ‘normal’ level is likely to postpartum period associated with an increased risk of
be closer to 0.8 mL/kg/hr. Creatinine levels are within thrombus formation. Thromboembolic events remain a
48
the normal non-pregnancy range within 24 hours post- leading cause of maternal death in developed coun-
partum, whilst the lower urea levels remain for at least tries. 24,52 A number of changes to the haemostatic system
46
48 hours. The bladder returns to the pelvis in the early occur during pregnancy (Table 26.3).
postpartum period as the uterus and other organs resume Of note, gestational thrombocytopenia – a platelet level
their pre-pregnancy position. between 80–150 × 10 /L – occurs in 6–8 % of women. 53,54
9
It generally has no negative impact on the woman or fetus
GASTROINTESTINAL SYSTEM AND LIVER at these levels, as there is no pathology associated with
The uterus pushes abdominal organs aside as it advances the low platelet count. 55
making assessment and diagnosis of an acute abdomen
difficult. For example, the appendix is progressively
displaced upwards and laterally from McBurney’s point
at the third month, reaching the level of the iliac crest
by late pregnancy. The bowel and other organs are gen-
49
erally displaced by the enlarging uterus; women with TABLE 26.3 Haemostatic changes during
56-58
prior abdominal surgery and adhesions are predisposed pregnancy
50
to intestinal obstruction as a result. Additionally, there
is an increase in intraabdominal pressure which may Haemostatic component Changes during pregnancy
contribute to another common pregnancy symptom, Platelets:
heartburn. Count Unchanged
Function and lifespan Unchanged
Generalised smooth muscle vasodilatation occurs Clotting factors:
throughout the gastrointestinal tract including sphinc- Factors VII, VIII & IX Increased
ters. Thus there is delayed stomach emptying and a lax Fibrinogen Doubles by term
cardiac sphincter leading to an increased likelihood of Other clotting factors Mainly unchanged
aspiration. The bowel has slowed peristalsis resulting in Fibrinolysis:
constipation, common in many pregnant women. The D-Dimer level Progressively increases
vasodilatation of blood vessels in combination with con- throughout pregnancy
stipation increases the incidence of haemorrhoids during By term, level >0.5 mg/L
pregnancy. common