Impact of medically assisted fertility on preterm birth.

Preterm birth is a frequent problem in women who undergo treatment for infertility. Many factors appear to contribute to the occurrence of this complication. Infertile women seem to have a predisposition to giving birth preterm and to having low birthweight babies. These complications also occur in women with a history of infertility who achieve pregnancy without treatment and who have singleton pregnancies. Assisted reproduction patients treated with in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) have a disproportionately high occurrence of preterm births even with singleton pregnancies. Spontaneous preterm labour may be related to underlying medical conditions of the female partner, as its occurrence is not increased in subjects treated with ICSI (i.e. when the infertility problem is associated with male reproductive dysfunction in normal female partners). Multiple pregnancy is the factor most likely to be related to preterm birth in infertile women. The administration of drugs to induce ovulation either alone or combined with intrauterine insemination causes a significant increase in multiple pregnancies. The occurrence of higher order multiple pregnancy is also increased. Multiple pregnancy in women undergoing IVF or ICSI is related to the number of embryos transferred at the end of treatment. The transfer of more than two embryos in women under 35 is not associated with an increased chance of conception, while the occurrence of multiple pregnancy is significantly increased. Women over 40 may benefit from the transfer of more than two embryos, with fewer risks of multiple pregnancy. Single embryo transfer is increasingly considered a workable clinical option, particularly in young women. Hopefully, a more cautious approach to infertility management will reduce the occurrence of multiple pregnancy, spontaneous preterm labour and the high number of low birthweight infants born after treating these women.