Renal Disease in Pregnancy

Renal disease can affect the outcome of pregnancy, pregnancy can affect the progression of pre-existing renal disease, and pregnancy can itself cause renal impairment. The renal system undergoes significant physiological and anatomical changes during a normal pregnancy:

• Renal plasma flow increases by 50-70% in pregnancy (the change is most pronounced in the first two trimesters).
• There is an increased glomerular filtration rate (GFR), which peaks at about the 13th week of pregnancy and can reach levels up to 150% of normal.
• Therefore, both urea and creatinine levels are decreased.
• Increased levels of progesterone at the beginning of pregnancy increases relaxation of arterial smooth muscles and so decreases peripheral vascular resistance, causing a blood pressure fall of approximately 10 mm Hg in the first 24 weeks of pregnancy.
• A change in tubular function with increased glycosuria also occurs (see below).
• The anatomical changes are mainly in the collecting system. A dilatation of the ureters and pelvis occurs, which can lead to urinary stasis and an increased risk of developing urinary tract infections.
• There is also an increase in overall kidney size by about 1-1.5 cm.
• In general, the physiological changes peak by the end of the second trimester and then start to return to pre-pregnancy levels; anatomical changes generally take up to 3 months postpartum to subside.

• Values considered normal when not pregnant may reflect decreased renal function in pregnancy. Creatinine above 75 micromol/L and urea above 4.5 mmol/L are indications for further investigation.¹
• Glycosuria is common and does not usually indicate diabetes or impaired glucose tolerance.
• Urinary protein excretion increases during pregnancy, but never to more than 300 mg/day; and therefore overt proteinuria is abnormal.
• Women are at increased risk of UTI because of renal tract dilatation leading to urinary stasis, and this should be treated promptly.

• Asymptomatic bacteriuria is found in 2% of sexually active women, and is more common (up to 7%) during pregnancy.
• Because of the dilatation of the calyces and ureters that occurs in pregnancy, 25% will go on to develop pyelonephritis, which can cause fetal growth restriction, fetal death, and premature labour.
• If asymptomatic bacteriuria is present on 2 MSUs, antibiotics, e.g. amoxicillin or nitrofurantoin should be given, depending on sensitivities and allergies.
• Pyelonephritis is common at around 20 weeks and in the puerperium.
• 20% of women having pyelonephritis in pregnancy have underlying renal tract abnormalities and an IVU or ultrasound at 12 weeks' postpartum should be considered.

• Women with only mild renal impairment from any cause will usually have a successful pregnancy outcome, and will seldom incur any additional renal damage as a result of the pregnancy.
• Some women, however, will have complications during the pregnancy itself, especially hypertension (see article Hypertension in Pregnancy).
• Women with more severe renal impairment are more likely to suffer hypertension , pre-eclampsia or premature labour, and to have a small baby, miscarriage or irreversible decline in renal function in the long term.¹
• Pregnancy is extremely uncommon in women with end stage renal failure on dialysis, for a variety of reasons; most such women are infertile. Fertility often returns rapidly after a successful renal transplant.
• If women on dialysis do become pregnant, the outcome is usually poor with a very high risk of miscarriage, severe hypertension, small babies and prematurity.² A 50% increase in dialysis is needed. Live birth outcome is only about 50%. Outcome is better for those with renal transplants.³
• Medications, especially antihypertensive agents, must be reviewed in women with renal disease who wish to get pregnant, and additional aspirin, anticoagulation or antibiotic prophylaxis may be required.

• Pregnancy itself can cause acute renal failure and renal disease can present for the first time during pregnancy.
• Women should be investigated as normal. Renal biopsy, if indicated, is considered safe.
• Acute renal failure in pregnancy may be due to various causes, including:
  • Septicaemia, e.g. septic abortion, pyelonephritis
  • Haemolysis, e.g. sickling crisis, malaria
  • Hypovolaemia, e.g. pre-eclampsia, antepartum haemorrhage, intrapartum or postpartum haemorrhage, DIC, abortion

• Reflux nephropathy
  • Prophylactic antibiotics are required
  • Potential for inheritance
• Systemic lupus erythematosus
  • High risk of spontaneous abortion
  • May need immunosuppression drugs
  • Problems for fetus (e.g. neonatal lupus, heart block)
• Diabetic nephropathy
  • Deterioration of hypertension
  • Increased risk of pre-eclampsia
  • Accelerated decline in renal function
• Kidney transplant recipient
  • Increased risk of miscarriage in first trimester
  • Risk from some immunosuppressants (e.g. mycophenolate mofetil)
  • Increased risk of hypertension
  • Premature delivery