Further analyses showed that having a low-birthweight infant and preeclampsia were additive risk
markers for ESRD (Table 3). Because of the small number of subjects in individual categories, it was not possible to stratify analyses of women with more than one pregnancy according to the particular pregnancy or pregnancies complicated by preeclampsia and by having a low-birth-weight infant.When these analyses were repeated for preterm birth, the results were similar to those for having a low-birth-weight infant (see the Supplementary Appendix, available with the full text of this articleat www.nejm.org). There were no significant interactions between the effects of preeclampsia and having a low-birth-weight infant on the risk of ESRD. We also looked at the effect of having a small-for-gestational-age infant on the risk of ESRD and found that the association was weaker than that with having a low-birth-weight or preterm infant (i.e., the association was significant only after one pregnancy; data not shown).