The risk of preterm delivery is increased in patients who have received RT (Tables I and II), however, in one of the largest studies of cancer survivors in Finland, AP RT increased the risk of preterm delivery in paediatric and adolescent cancer survivors, but not in adult cancer patients receiving the same exposure (3/21; OR 2.44, 95% CI 0.67-8.92). Interestingly, in the young adults (20-34 years old) age group, risk of preterm delivery was significantly elevated among 37/452 patients whose treatment regimens did not include RT (OR 1.49; 95% CI 1.03-2.15). 
Successful pregnancies and deliveries of healthy children in women who have had SCT and preconditioning with TBI are well documented. However, due to reporting bias, the true incidence of pregnancy-related complications after SCT is unknown. In a large study of more than 35 000 European men and women who received SCT, there were 122 babies born to 113 women, of whom 23 had TBI. Increased pregnancy risks were seen in those who had received TBI compared to the general population and included preterm delivery (45% vs 6%, respectively) and LBW (50% vs 6%, respectively). Surprisingly, these risks appear to be much higher compared to abdominal RT and demonstrate that more study is required in this area.
Similarly, studied a group of 708 post-pubertal women who had received TBI for haematological malignancy. Among these, 110 had ongoing ovarian function and there were 32 spontaneous pregnancies. There was an increase in spontaneous miscarriage (38% vs 4%, respectively P = 0.02) and preterm delivery (63% vs 18%, respectively P < 0.02) among those receiving TBI with high-dose alkylating agents compared to alkylating agent treatment alone. An increased incidence of LBW and very LBW in babies compared to that expected in the general population (25% vs 7%, respectively P < 0.0001) was noted in those receiving high-dose alkylating agent, with or without TBI. Comparing the fertility of haematological malignancy survivors to their closest age siblings, demonstrated a reduced number of pregnancies in survivors (3% vs 72% in siblings, P < 0.0001), at least partially explained by ovarian damage, and an increased prevalence of nulliparity with later exposure to SCT or exposure to TBI. In contrast to the other studies (albeit with smaller numbers, i.e. n = 14), no significant increase in miscarriage, PTB or stillbirth was observed.
Radiation affects fertility by damaging the ovaries and uterus, and their separate effects are difficult to distinguish. It appears that the LD50 (i.e. the dose required to kill 50% of oocytes) is 2 Gy or less in humans. The age-related response of the uterus and ovary to RT seems to differ. There appears to be an increase in radio-resistance of the uterus with age, but a decrease in resistance of the ovary to irreversible effects. This is evidenced by the fact that the sterilizing dose at which POI occurs immediately after treatment declines with age. Thus a younger patient with a larger oocyte reserve will have a larger residual reserve following treatment. The sterilizing dose for women aged less than 20 years is approximately 15 Gy. A study of fertility outcomes in 84 patients who had received abdominal and/or pelvic radiation in childhood, suggested that doses of less than 4 Gy caused no damage, while 4-15 Gy put patients at risk of subfertility.
When considering the uterus, doses between 14 and 30 Gy can impair uterine function; however, this also occurs with lower doses in TBI (approximately 12 Gy), as described below. Doses for the treatment of rectal and cervical cancers are usually 30-50 Gy and a dose of >40 Gy has been traditionally regarded as sterilizing to the uterus. The tumour types and doses are summarized in Table I. Notably, there have been reports of successful pregnancies at doses of 30-54 Gy (see Table II). The main limitation is that the maximal radiation dose delivered to the tumour does not necessarily correlate with the uterine dose absorbed. This depends on tumour location and uterine proximity. Thus, there will be individual variation, even for patients with the same tumour type. A radiation oncologist may be able to provide a better estimation of uterine dose exposure.