The greater the degree of renal dysfunction, the more likely the patient will 1) not become pregnant or 2) if already pregnant, have a greater chance of intrauterine growth restriction, or fetal demise. Generally, patients with creatinine's at or above 1.4-1.5 mg/dl are at higher risk for fetal complications, with some studies suggesting that creatinine levels > 3 mg/dl make it very difficult to become or sustain a viable pregnancy.
Thoughts about why infertility occurs in advanced CKD and ESRD patients include elevated 1) prolactin levels, 2) loss of the cyclical nature of FSH and LH secretion, and 3) loss of testosterone production (in males). Studies have not consistently demonstrated that hormonal replacement therapy leads to increased probabilities of becoming and maintaining a successful pregnancy. However, what has been shown to be of significant benefit is daily hemodialysis. Many studies, summarized in this review article, have indicated that daily hemodialysis (for up to 8 hours per night), or "as much dialysis as the patient can tolerate" have increased the probability of becoming pregnant. Of course, the fetus is still at risk for intrauterine growth restriction or premature birth (the most common outcomes for a fetus whose mother is ESRD).
Patients on peritoneal dialysis, however, have a lower likelihood of becoming pregnant than those on HD. Thoughts for why this occurs include: 1) dwell volumes that impair egg transport from the ovary to the fallopian tubes, 2) damage to the ovaries from the constant exposure to high-concentration dextrose in the dialysate, 3) impaired uterine expansion. It is interesting that PD patients have a lower rate of pregnancy than HD patients because studies have shown (in HD patients) that those with residual renal function (RRF) have a greater chance of becoming pregnant. In general, PD patients are more likely to have RRF than their HD counterparts, but in the case of pregnancy, the benefit of having RRF does not seem to be enough to overcome the negative effects of having dialysate in one's abdominal cavity.
Finally, many women can once again become pregnant and have a successful pregnancy to full-term after transplantation, particularly if their serum creatinine is < 1.5 mg/dl and they are able to avoid acute rejection episodes.