Decreased nutritional status, malnutrition
Persistent BUN >50 mg/dL
Blood urea nitrogen (BUN) levels, as well as uremic symptoms, play a major role in initiating dialysis in a pregnant woman with advanced chronic kidney disease (CKD). Prior studies have shown that BUN levels above 60 mg/dl are directly related to fetal mortality . In addition, higher BUN levels have been shown to have a negative effect on birth weight as well as gestational age [7, 8]. For this reason alone, a woman may be started on dialysis. In addition to initiating dialysis for this cause, increasing the frequency of dialysis in order to maintain a predialysis BUN less than 50 mg/dl is the usual approach. Maternal acidemia can also affect fetal outcome and has been associated with decreased Apgar scores and fetal distress . Hence if significant acidemia is present, dialysis can be initiated.
Residual renal function seems to play a role in improved fetal outcomes. All the 16 women with successful pregnancies reported by the European Dialysis and Transplant Association in 1980 had some residual renal function . In addition, women who conceive before starting dialysis showed a trend toward better fetal outcomes [11, 12]. These women were seen to have higher residual glomerular filtration rate . Okundaye et al. also showed that women who conceived before starting dialysis had a lower frequency of low birth weight babies and prematurity, as well as a higher rate of infant survival .
Modality Choice: PD or HD or Nocturnal Hemodialysis
Pregnancies in peritoneal dialysis (PD) women of childbearing age do occur, although rare. Etiologies for the decreased conception r ate on PD as opposed to HD include the presence of hypertonic fluid in the peritoneal cavity which may interfere with the transport of the ovum to the fallopian tube and prior episodes of peritonitis which may cause adhesions and thus interfere with implantation [13, 14].
Despite the rarity, if a patient on peritoneal dialysis conceives, it is preferable to keep that patient on PD. There were no significant differences seen with respect to infant survival, frequency of prematurity, or low birth weight babies for women who conceived on hemodialysis compared with those who conceived on peritoneal dialysis . Redrow et al. described several reasons why continuous ambulatory peritoneal dialysis (CAPD) is an acceptable dialysis modality for the management of renal failure in a pregnant woman as follows: (1) CAPD offers a stable environment for the fetus with respect to fluid and electrolyte balance; (2) due to the continuous nature of the modality, less blood pressure fluctuations occur decreasing the risk of placental underperfusion; and (3) women on CAPD may have less dietary restrictions . In 1988, Redrow et al. actually suggested PD as the recommended modality for a pregnant woman . Disadvantages of PD may include risk of peritonitis and the discomfort of the simultaneous presence of a large volume of dialysate fluid in the gravid abdomen.
Nocturnal hemodialysis (NHD), a type of intensive hemodialysis, can provide 8–10 hours of dialysis therapy 3 to 7 nights per week during sleep. Several reports from Toronto have shown improved fetal outcomes when NHD was increased to 5 to 7 nights per week and to 7–8 hours each session. In these women, gestational age at delivery was 36.2 +/− 3 weeks, and the mean birth weight was 2417.5 +/− 657 g .
When deciding on a dialysis modality, as in the nonpregnant patient with advanced CKD, the patient and physician must work together in choosing the dialysis modality which optimizes quality of life. In addition one must keep in mind and plan for the time needed to train and educate for a home modality. If a woman conceives while either on hemodialysis or peritoneal dialysis, there is no reason to switch that modality unless some specific problem or indication arises.
Total hours of dialysis per week have been shown to affect fetal outcomes. In 1998, Okundaye et al. showed that in women who received 20 or more hours of dialysis per week, there was a trend toward better infant survival, decreased prematurity, and higher birth weights . More recently, in a 2014 cohort comparison, live birth rate improved in each successive tertile of hours of hemodialysis provided, with a rate of 48% in women who received 20 hours or less to 85% in women receiving 37 hours or more on dialysis. Women who received 21–36 hours of dialysis had an intermediate live birth rate of 75%. Both birth weight and gestational age (mean 36 weeks) improved with more hours of dialysis received . In the most recent US national survey of nephrologists, most nephrologists now prescribe 4 to 4.5 hours of hemodialysis per session (average 4.2 +/− 0.9) for 6 days per week (average 5.5 +/− 1.1) .
Summary elements of a dialysis prescription in a pregnant dialysis patient
Typical dialysis prescription
4–4.5 hours per day, 6 days per week of hemodialysis
Unfractionated heparin with standard loading and maintenance hourly doses as long as there is no contraindication
Blood flow rate
Dialysis flow rate
137–140 mmol/L; dependent on serum sodium
Dependent on serum and ionized calcium levels
Dependent on serum potassium level; usually higher potassium bath (3K) is required in those receiving daily dialysis
Constant; avoid hypotension
Favors usage of AVF; if a catheter is present, graft placement is preferred to allow for early removal of the dialysis catheter
Intradialytic fetal monitoring (IDFM)
Once fetus is viable, IDFM is ideal for close monitoring of the fetus pre-, during, and post-dialysis
Due to the increased dialysis prescription, BUN is lower with daily dialysis. Higher BUN levels have been associated with adverse fetal outcomes, as already mentioned, as well as increased risk of bleeding due to uremic platelet dysfunction and fetal osmotic diuresis leading to polyhydramnios. Frequent dialysis can lead to hypokalemia and hypophosphatemia. Most women are told to liberalize the potassium or phosphorus in their diet if their serum levels of either potassium or phosphorus levels are low. If this does not resolve the imbalance, then higher potassium dialysate baths may be warranted. In addition, oral supplementation of phosphorus may be needed. We suggest checking electrolytes at least weekly in a pregnant woman on dialysis.
Anticoagulation During Dialysis
Although pregnancy is considered to be a hypercoagulable state, no studies have been conducted to assess clotting risk in this population when on hemodialysis. The usual practice is to administer the anticoagulant heparin to prevent clotting of the extracorporeal circuit . Heparin does not cross the placenta and is not teratogenic. Contraindications to heparin are the same as in a nonpregnant dialysis patient. These may include but are not limited to active or recent bleeding, presence of a coagulopathy, or low platelet count. Anticoagulation can be stopped as the woman approaches term so that if emergent surgery is indicated, there will be no bleeding complications.