Pregnancy in Dialysis Patients

Introduction: A Historic Perspective

When the first successful pregnancy in a woman on hemodialysis was reported in 1971 by Confortini and coworkers, the report elicited more skepticism than enthusiasm, and some nephrologists felt that emphasizing this exceptional occurrence could lead to the wrong expectations and might even be detrimental. In 1975, an editorial in The Lancet stated, “Children of women with renal disease used to be born dangerously or not at all—not at all if their doctors had their way.”

Having a child while on dialysis is still a very rare event, albeit no longer such an exceptional one, and the interest in this particular niche of dialysis management has implications that go far beyond the technical aspects. These implications involve the concept of dialysis efficacy, as well as social aspects, including the different attitudes towards pregnancy in diverse cultural settings and the limits of dialysis availability in highly as well as poorly resourced countries.

In this chapter, we will summarize what we know and agree on, and what we do not know, or is a matter of controversy, on the main aspects of dialysis in pregnancy: epidemiology and main maternal-fetal results, indications for dialysis start in pregnancy, dialysis schedules, nutritional approaches, psychological aspects, and data on children of on-dialysis mothers.

Evidence-Based Medicine and Pregnancy on Dialysis: Methodological Insights

Evidence regarding pregnancy on dialysis is limited and mainly derived from observational studies. Obviously, pregnancy itself cannot be randomized; for evident ethical reasons, randomization of any kind of treatment in pregnancy is complex, and ethical barriers are more often present in this context than in other areas of nephrology and dialysis. As a consequence, we do not have, nor do we expect to have in the future, randomized controlled trials on dialysis duration, frequency, schedule, or on obstetric monitoring policies.

Rare events are, by nature, either reported by large multicenter sources, registries or cross-linked databases or in small series or case reports. Large series frequently lack clinical details and are often highly heterogeneous. Case reports and small series are more likely to be affected by reporting and publication biases: the happy ending of a rare event prompts communication, but the opposite is true in the case of catastrophic events, such as the loss of mother and/or child. As such, case reports and small series should be taken as a marker of what is possible but can be hard to translate into the true probability of success.

The “physiological” lack of randomized controlled trials, the rarity of the event, and the heterogeneity of the sociocultural background and clinical approaches are also reflected by the limited number of available guidelines or best practices. To the best of our knowledge, only the Italian Society of Nephrology dedicated one of its five best practices on pregnancy and the kidney to pregnancy on dialysis, while one guideline from the U.K. is dedicated to the entire topic of chronic kidney disease (CKD) in pregnancy and includes the dialysis issue. Conversely, the National Institute for Health and Care Excellence (NICE) Guidelines on intrapartum care for women with existing medical conditions or obstetric complications and their babies dedicate a short paragraph to acute kidney injury and CKD.

Epidemiologic Aspects of Pregnancy on Dialysis

Frequency of Pregnancy in Dialysis Patients

Since pregnancy is considered a rare, if not exceptional, occurrence on dialysis, many dialysis registries do not record this event, the exception being the Australian and New Zealand Registry, which is now one of the most important sources of epidemiological information in this regard. However, early pregnancy abortions or miscarriages may escape being recorded, large-scale and systematic information on conception is not available, and epidemiological data mainly regard pregnancies that go beyond the second trimester.

Within these limits, two concordant studies, one from Italy and one from Australia, albeit with a different study design (nationwide survey in Italy and registry data in Australia), suggest that there is a 1:10:100 gradient in birth rates between dialysis, kidney transplantation, and the general population. In other words, the probability that a woman of childbearing age on dialysis will deliver is about 1:100 compared to the overall population of the same geographic area. While the two studies come from culturally and geographically different settings, they were both performed in countries in which dialysis, and related care, is available without restriction for all patients. Less is known about those countries in which dialysis access is nonuniversal.

Recent data from the United States report an increase of pregnancies in women on renal replacement therapy, both on dialysis and after kidney transplantation, in the period 2002–15. The reasons for this phenomenon are not clear, and the fact that it involves both dialysis and kidney transplantation suggests that the increase is not merely driven by the better results obtained in dialysis and that different sociocultural issues are involved.

The importance of cultural and social aspects has been highlighted by several sources. Indirect clues come from the increasing number of pregnancies reported in patients on dialysis in Latin America or the Arab world, where yearly pregnancy rates on dialysis may be higher. Indeed, in both settings, the attitude towards pregnancy is characterized by a cultural drive towards large families and a lower influence on social life by “invisible diseases,” such as end-stage kidney disease (ESKD).

Recent data from a study performed in a large U.S. cohort between 2005 and 2013 with an unexpectedly high pregnancy rate (17.8 per 1000 patient years) showed pregnancy was associated with belonging to an ethnic minority or living in a low-income area. In keeping with a higher probability of becoming pregnant for a woman from a disfavored milieu, one-third of these pregnancies were “lost to follow-up.” The intriguing association between pregnancy and belonging to a low-income, minority strata of the population, which is in turn associated with lower adherence to the medical prescription and counseling, raises the question of whether this reflects a difference in reference values, such as the importance of large families or a lower probability of being influenced by the health care team, whose opinions on pregnancy in dialysis are frequently reductive.

Notwithstanding the sociocultural aspects, according to the few large-scale reports, pregnancy is more frequent, and its outcomes are more often favorable when conception occurs before the start of dialysis or in the first months/years after dialysis initiation. The presence of some residual kidney function or, at least, residual diuresis is associated with better outcomes. However, successful pregnancies have also been reported in women with a long dialysis vintage on peritoneal, as well as on hemodialysis (as will be further discussed regarding dialysis schedules) and in the context of all types of kidney diseases, including those, like lupus nephropathy, which are often associated with poorer outcomes.

This complex network of sociocultural and medical issues may be summarized as follows.

What we know:

Pregnancy on dialysis is a rare event.
The frequency of delivery may be estimated at about 1:100 with respect to the overall population of the same geographic area, at least in highly-resourced countries.
While pregnancies are more frequently reported and more frequently successful in women who have recently started dialysis and who have some residual kidney function, successful pregnancies have been reported in women affected by all kidney diseases, at different ages and dialysis vintages.

What we do not know:

What the incidence of early fetal loss and elective pregnancy termination is.
What the differences in fertility and delivery rates around the world are.
What the influence of the social and cultural background is.
What the role of medical counseling in favor or against pregnancy is.

Maternal and Fetal Outcomes

The likelihood that a pregnancy in a dialysis patient ends with the “baby in mother’s arms” is increasing and strongly depends upon the dialysis schedule, as will be shown in the following paragraphs.

Until the new millennium, the reported chances that pregnancy in a dialysis patient would end successfully progressively increased from 23% in a report by the European Renal Association-European Dialysis and Transplantation Association (ERA-EDTA) in 1980, comprising 115 pregnancies in dialysis, to approximately half of the pregnancies in a nationwide series published in 1998. In 2008, a systematic review focusing on the outcomes in the new millennium retrieved only 90 cases, with an overall probability of a healthy offspring ranging from 50% to 100% (overall 76.3%). After that, reports sharply increased, and about 1000 pregnancies in dialysis patients were reported between 2000 and 2020. The most recent systematic review available in this issue, published in 2016, gathered almost 700 pregnancies in the new millennium and confirmed a success rate of about 80%.

However, the reporting bias might be critical, and the available literature can be considered informative mainly on cases that go beyond the first trimester, since it is likely that information on early miscarriages is missing.

In keeping with what is observed in non–dialysis-dependent CKD, preterm delivery is almost the rule (83% in the meta-analysis), and the birth of a small for gestational age baby is likewise frequent (over 30% of cases on hemodialysis in the same review; the incidence is higher on peritoneal dialysis [PD] and was rated at about 60%).

There seems to be no excess mortality in mothers who had a baby while on dialysis versus other women on dialysis; however, the long-term impact of having had a pregnancy, against the background of increased mortality in dialysis patients, is not known.

The risk of developing or worsening hypertension during pregnancy is high. Defining preeclampsia in dialysis patients is, however, difficult, if not impossible. In any case, against the background of kidney disease, we are dealing with “superimposed preeclampsia,” and furthermore, proteinuria is not a reliable marker in this context, even in patients with residual kidney function. Moreover, attributing new development or worsening of hypertension to pregnancy is difficult due to the interference between blood pressure and water and sodium homeostasis. Moreover, the biomarkers that are increasingly being employed in assessing the risk of preeclampsia should be considered with skepticism in dialysis patients since their behavior is not fully known, and relying on laboratory data alone may be misleading. Taking into account these caveats, we suggest monitoring s-flt1 and placental growth factor (PlGF) starting in the 20th pregnancy week (in many countries there is a ban on earlier testing), as these biomarkers may indeed reflect placental health, and their normality may point clinical management toward pharmacological intervention and modulation of the dialysis prescriptions. A putative algorithm, merging utero-placental flows, fetal growth, and biomarkers, is reported in Fig. 57.1 .

Fig. 57.1, A proposed diagnostic algorithm in the case of development or worsening of hypertension in pregnancy in a dialysis woman.

Once more, in keeping with the data reported in the population with CKD not on dialysis, there is no evidence of an increased risk of congenital abnormalities other than those expected in cases of genetic kidney diseases (including, among others, polycystic kidney diseases and congenital anomalies of the kidney and urinary tract).

Current evidence suggests that the prognosis of children born to on-dialysis mothers is mainly linked to prematurity and intrauterine growth restriction: Fig. 57.2 is a remake of a classic illustration of the association between prematurity and neurological deficits, which can be of use in counseling. Besides some neurological disorders associated with prematurity (in the most severe cases presenting with cerebral hemorrhage), being born very preterm or small for gestational age, especially if linked to intrauterine growth retardation ( Fig. 57.3 ), is associated with an increased risk of developing hypertension, obesity, metabolic syndrome, or CKD in adulthood. This observation may be of particular concern for families already faced with the challenges of CKD. The reasons behind this association are not fully understood; however, not attaining an adequate number of nephrons provides the main physiopathological background for the future development of hypertension and kidney disease, while late maturation of fat tissue may be at the basis of the increased risk of obesity and metabolic syndrome. The risks do not seem to be different in on-dialysis mothers with respect to other situations with similar degrees of prematurity or growth restriction; however, the evidence is only indirect and fragmentary.

Fig. 57.2, Patterns of probability of survival and of risk of major and minor neurologic deficits in premature babies.

We have only very limited information on the health of children born to on-dialysis mothers. Psychosocial health was analyzed in only one study and seemed comparable with the general population. Another study analyzed kidney health, leading to the identification of an increased risk of albuminuria, whose long-term effect on kidney health remains to be assessed.

Table 57.1 reports the main elements associated with a favorable prognosis in pregnancies in on-dialysis mothers; however, it has to be underlined that successful pregnancies have been reported in all types of kidney disease, with and without residual kidney function and on all dialysis modalities. The success rate is indeed more closely linked to the intensity of dialysis than to the baseline clinical characteristics of the mother; thus, attention has shifted to dialysis management, as will be further discussed.

Table 57.1

Prognostic Elements of Pregnancy on Dialysis

	What We Know	What We Do Not Know—Comments
Residual kidney function	Scattered data suggest that the presence of good residual kidney function is associated with better pregnancy outcomes.	The differences in residual function may be offset by intensive dialysis. If this is not the case, the differences may be due to lower accumulation of larger molecules (the “middle molecules,” only partially cleared by dialysis) or to lesser volume changes during hemodialysis.
Short dialysis vintage	Lower uremia-related comorbidity and higher residual kidney function are expected in these patients.	The role of each element is difficult to disentangle.
Non-immunologic disease	Prognosis of pregnancy in CKD is overall better in nonimmunologic diseases; hence, the same may be the case in on-dialysis patients.	Dialysis is often considered as offsetting the effect of immunologic diseases. We do not know if this is true in pregnancy.
Younger age	Pregnancy-related risks increase with age. It is reasonable to infer that younger dialysis patients, who usually also have a shorter exposure to uremia, may have a better prognosis.	There are no specific data on the age effect in on-dialysis patients. Indeed, age is an important issue in pregnancy on renal replacement therapy (see text—ethical issues)
Normotension	Baseline blood pressure levels are important determinants of the prognosis of CKD pregnancies.	Hypertension in dialysis patients is usually volume dependent, and its control is easier on daily dialysis. The role of the different pathogenesis of hypertension (volume dependent versus pregnancy induced) is not clear.
Good compliance	Adhering to and understanding prescriptions are fundamental for managing the demanding dialysis schedule.	The different outcomes reported in settings where patients are referred when they specifically want to have a child, and unwanted pregnancies may underline the importance of the compliance issue.

CKD , Chronic kidney disease.

What we know:

A successful pregnancy in a dialysis patient, defined as “baby in mother’s arms,” meaning that mother and child are both well and returning home, is possible and is increasingly frequent (over 75% of cases).
There is no excess mortality after delivery for an on-dialysis mother.
There is no excess of malformations in children of on-dialysis mothers (besides the presence of genetic diseases leading to kidney failure in the mother).
Preterm delivery is almost the rule (over 80%), and intrauterine growth restriction is present in about half of the cases;
A successful pregnancy is possible in all kidney diseases, both on PD or hemodialysis and also with a long dialysis vintage; however, younger age, short dialysis vintage, residual kidney function, and normal blood pressure are probably associated with better outcomes.
The short-term risks for children are linked to prematurity and intrauterine growth restriction; the neurological risks are mainly associated with the degree of prematurity.
Prematurity and intrauterine growth restriction are associated with metabolic syndrome, hypertension, and CKD in adulthood; these risks do not seem to be different in on-dialysis mothers with respect to other situations with similar degrees of prematurity or growth restriction.

What we do not know:

We have only partial data on early pregnancy loss, so our knowledge of the first phases of pregnancy is limited.
We have no evidence allowing quantification of the importance of factors that are known to affect pregnancies in CKD patients not on dialysis (age, kidney disease, etc.).
We have very limited information on the long-term health of children of on-dialysis mothers.

Diagnosis of Pregnancy, Prenatal Screening, and Assisted Fertilization in Dialysis Patients

The term “diagnosis of pregnancy” may sound funny at first since pregnancy is not a disease, and its signs are usually rapidly evident. The latter may, however, not be true in young women on dialysis and for several reasons: the hormonal derangements commonly observed in ESKD are usually associated with irregular menses, and a missed menstrual cycle does not immediately evoke pregnancy; intermenstrual bleeding is frequent and may mimic menses; the idea that dialysis is associated with infertility may reduce awareness of the possibility of getting pregnant. Indeed, in the Italian series, more than half of recorded pregnancies were unplanned, and similar results were reported in the United States. On the other hand, in the Canadian experience, some women are “prepared” for pregnancy by increasing dialysis frequency. While there is little published evidence to support this approach, the rationale is sound since intensive hemodialysis is able to restore the hormonal milieu, presumably facilitating pregnancy.

The background levels of beta-human chorionic gonadotropin (beta-hCG), which is usually employed in the confirmation of pregnancy, are increased in dialysis patients, even in nonpregnant ones. Beta-hCG is produced in small amounts in men and nonpregnant women, primarily by the anterior pituitary gland; beta-hCG is a “middle molecule,” a term that indicates a molecule of molecular weight between 500 and 60,000 Daltons, which accumulates in severe CKD.

In this context, pregnancy dating mainly relies on echography signs. Being on dialysis does not affect the initial phases of embryonic development; therefore, early ultrasound assessment is as reliable as in other pregnancies. Conversely, in later pregnancy phases, in which pregnancy is often not discovered in dialysis patients, the onset of intrauterine growth restriction may interfere with pregnancy dating, which can, in turn, complicate pregnancy management.

Experience in prenatal screening is limited in these pregnancies.

Amniocentesis and chorionic villus sampling remain the gold standard.

Since amniocentesis and chorionic villus sampling are considered as bearing a 1% risk of miscarriage, other options are increasingly being explored, in particular, planned and often long-awaited pregnancies. Noninvasive prenatal screening for Down syndrome has a high rate of false positives due to the increase in the background levels of both beta-hCG and pregnancy-associated plasma protein A (PAPP-A). PAPP-A is a biomarker of inflammation and is associated with cardiovascular and all-cause mortality in dialysis patients.

Screening for fetal chromosomal derangements through cell-free circulating DNA (cfDNA) in the maternal plasma represents an appealing potential alternative for patients on dialysis, but there is only very little experience in this regard. Indeed, on account of its molecular weight, cfDNA could be at least partially cleared by hemodiafiltration or by hemodialysis with highly permeable membranes. In addition, little is known about maternal cfDNA release during dialysis (i.e., acute and chronic inflammation as in peritonitis, immune and autoimmune diseases, vascular diseases, etc.), which could affect the maternal to placental cfDNA ratio (the so-called fetal fraction [FF]) and cfDNA test sensitivity. While waiting for further data, if this approach is chosen, its limits should be highlighted, and collaboration with an experienced obstetrical team is mandatory.

While a discussion on contraceptive use in dialysis is beyond the scope of this chapter (we may suggest referring to the recent Italian best practice for contraception in kidney diseases for details), it is important to remember that this issue should be systematically touched upon in dialysis patients in order to identify the most suitable birth control strategy.

In women who wish to get pregnant, besides providing intensive dialysis and monitoring hyperprolactinemia, baseline assessment of beta-hCG may be of interest to allow for reliable monitoring of the first phases of pregnancy; we suggest gathering at least two to three measurements since the behavior of this middle molecule in dialysis patients is only partially known. Furthermore, women should be warned that they need to report not only the classic symptoms of nausea and breast tenderness but also any reduction in blood pressure, fatigue, and/or increased need for erythropoiesis-stimulating agents.

Assisted fertilization is increasingly being employed in situations in which fertility is reduced, in particular when the mother’s age is high, and the ovarian reserve is low. Reports on dialysis patients are very limited and, as occurs with rare events, reporting and publication biases are once again substantial, limiting the information to favorable cases; conversely, women may not wish to openly discuss these issues, and underreporting may also be an issue. Despite these caveats, happy endings have been reported, at least confirming feasibility, but without allowing for any conclusions to be made regarding risks and success rates.

The potential contraindications in women on dialysis are mainly linked to the hormonal conditioning that is usually part of the assisted fertilization techniques. Indeed, the features of ovarian hyperstimulation syndrome (hyperhydration, edema, ascites, and hypercoagulability) may be particularly challenging in dialysis patients. Attention to fluid management, avoiding overzealous dehydration since the main weight gain is due to interstitial edema, and care in normalizing blood pressure is particularly relevant in these phases. In vitro fertilization may be proposed on spontaneous cycles with lower risks but also with lower chances of success. Once more, there is a strong need for a coordinated nephrology and obstetrical work-up.

What we know:

Detecting (or “diagnosing”) pregnancy in dialysis patients may be difficult by the standard tests.
Ultrasound pregnancy dating is reliable in the first weeks but may later be affected by intrauterine growth restriction.
The gold standard for detection of chromosomal abnormalities remains amniocentesis or chorionic villus sampling, bearing, however, a risk of miscarriage.
Assisted fertilization may result in successful pregnancies, even if only scarce experience is available on this issue.

What we do not know:

Noninvasive prenatal screening for Down syndrome, an alternative to amniocentesis or chorionic villus sampling in the overall population, has not been sufficiently explored in dialysis patients.
The risk of ovarian hyperstimulation in assisted fertilization may be higher in dialysis patients, but its incidence and severity are not known.
If and how intensive dialysis may be used to improve fertility are not known, even if this is a logical clinical approach.

When to Start Dialysis in Pregnancy

Very few issues are more controversial in the field of obstetric nephrology than the indications to start dialysis in pregnancy.

These indications need to balance and combine several different issues.

The first one regards the superior results obtained in women on chronic dialysis who underwent an intensive hemodialysis strategy. For this reason, we will only refer to hemodialysis starts in pregnancy, discussing the option of continuing PD in pregnancy in the next paragraph.

The second point is the caution toward the early start of dialysis that changed the approach to dialysis initiation in the nonpregnant dialysis population.

The third issue is the possibility of using nutritional management to delay the need for dialysis start, both in the overall population and in pregnant women.

Of interest, the team with the most experience in intensive dialysis in pregnancy (the Toronto group in Canada) and the team with the most experience in nutritional management to delay dialysis starts (the Torino group in Italy) are presently collaborating in a multicenter study to compare the results of these two nonmutually exclusive approaches. While waiting for the results of such a study, this chapter critically summarizes the main experiences and matters of discussion.

An important point concerning dialysis starts regards the way kidney function is analyzed in CKD pregnancy. In fact, in pregnancy, there is no agreed-upon formula for assessing the estimated glomerular filtration rate (eGFR) from serum creatinine, and even the use of creatinine clearance, based upon 24-hour urine collection, is not devoid of problems, in particular when it comes to a clearance of less than 15 mL/min. In this context, some authors suggest that the estimate of kidney function is more reliable if the mathematic mean between urea and creatinine clearance is employed. However, urea clearance is affected by diet, with a risk of underestimation, in particular in patients with lower protein intake.

Urea levels are currently employed as markers of adequacy in the intensive dialysis schedules of pregnancy; as a consequence, the definition of the need for dialysis starts as determined by urea levels is increasingly frequent. This pragmatic choice is not supported by sound evidence, and also, on account of the different normal values employed, the data in the literature are somehow heterogeneous. A reasonable approach is to combine more than one measurement, including urea (or blood urea nitrogen [BUN]) levels, urea and creatinine clearances based on 24-hour urine collection, and the analysis of other elements (such as blood pressure and hydration status, nutritional status, acidosis, calcium–phosphate and parathyroid hormone [PTH] balance, anemia monitoring, etc.) that are usually employed to establish the indications to start dialysis in the nonpregnant CKD population.

There is no doubt that once dialysis is started, intensive hemodialysis is associated with the best results. The shift from “as much dialysis as possible” to “dialysis as early as possible” may be logical, and it is on these bases that some authors suggest starting dialysis in pregnancy at the urea level that corresponds to the predialysis target indicated in the Toronto studies. While urea levels are highly dependent upon diet and on the metabolic pattern of each individual, a urea level of about 100 mg/dL or a BUN of about 50 may correspond to an eGFR between 20 and 30 mL/min, much higher than the eGFR considered for early (about 15 mL/min) or late (less than 6–8 mL/min) dialysis start.

Indeed, the indications for dialysis start are presently shifting toward a policy of “intent to defer” dialysis initiation, considering that the early start of dialysis seems to be associated with more harm than good, at least in the usual population of elderly and high-comorbidity patients. The growing evidence on incremental dialysis start suggests that a stepwise approach may limit morbidity and reduce the loss of residual kidney function, one of the elements more closely associated not only with survival on dialysis but also with successful pregnancies in dialysis patients.

We strongly believe that, outside of the context in which dialysis is needed to allow better volume and blood pressure management, the benefits of renal replacement therapy on pregnancy outcomes should be weighed on an individual basis versus the potential threats of catheter-related complications if dialysis is started with a central venous access of the surgical intervention for fistula placement and the overall dialysis-related morbidity. The risk-benefit balance may also be modulated by the phases of pregnancy and in settings with or without easy access to dialysis treatment ( Fig. 57.4 ).

Fig. 57.4, Start of Dialysis in Pregnancy: Pros and Cons.

The third element that could be integrated into this discussion is diet.

The rationale for integrating the nutritional management of advanced CKD in pregnancy with the choice to start dialysis in pregnancy derives from acknowledging the strict relationship between urea levels and pregnancy outcomes on intensive hemodialysis.

Since dietary protein intake is the main determinant of urea levels, a diet that merges moderate protein restriction with the attainment of the caloric goals and that shifts from animal to mainly plant-based food, with attention to the food quality (including avoiding prepared, canned, or preserved food), may help postpone the need to start dialysis in pregnancy. This experience, mainly carried out by the Torino and the Mexico City teams, may be of particular interest in cases in which the evolution of kidney disease is slow, and the patient shows good compliance. The lack of vascular access or the limited access to chronic renal replacement therapy may also weigh in the choice to attempt nutritional management before elective dialysis starts. Of note, in carefully monitored cases with advanced CKD, the use of such a plant-based, moderately protein-restricted diet has been associated with better preserved fetal growth as compared with unrestricted diets. However, to overcome the risk of malnutrition, dietary management needs to be integrated with strict clinical and laboratory follow-up, including check-ups at least as frequent as those prescribed in patients managed with an early dialysis approach. These options may be further combined in an incremental dialysis start ( Fig. 57.4 ).

On account of the clinical and psychological complexity and of the relevance for the quality of life of the patients, our current recommendations favor a personalized approach to dialysis starts, in the absence of clear signs of uremia, electrolyte derangements, or hydro-electrolyte load, considering the availability of dialysis, the availability of nutritional management, the experience of the team, and, of course, the patient's choices.

While, for the reasons mentioned earlier, we cannot set specific cut-offs for the discussion on dialysis start, we suggest that the alternative options be discussed at least in the eGFR window of 10–30 mL/min.

Conversely, the grim experiences where a clearly needed dialysis start is postponed only for logistic reasons or for the lack of the patient’s adherence, as reported from Mexico, demonstrate that once dialysis is needed, it should be started promptly to try to improve maternal and fetal outcomes.

What we know:

Evaluation of kidney function in pregnancy is challenging, and different tests should be employed to define it.
Dialysis may be needed in pregnancy, and its start is not associated with side effects other than those observed even out of pregnancy.
A carefully monitored, plant-based, moderately protein-restricted diet may allow postponing dialysis start in pregnancy without detrimental effects on fetal growth.

What we do not know:

Whether there is a single cut-point for dialysis starts in pregnancy and what it is.
Whether dialysis in pregnancy, in the presence of relevant residual kidney function, has to be started at full doses or in an incremental way.
Whether there are differences in the results of the short-term (pregnancy duration, fetal growth) and long-term outcome of the offspring according to the chosen earlier or later dialysis start.
Whether there are differences, especially in the range of the 10–30 mL/min of eGFR, between pregnancy outcomes employing a well-conducted nutritional assessment and an intensive dialysis schedule.

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