Multiple pregnancies resulting from assisted reproductive manoeuvres are often blamed for the rising preterm delivery rates in developed countries. Indeed, a multiple pregnancy is deemed to be the most significant risk of in-vitro fertilisation.
Transferring two or more embryos at the day 2 single-cleavage stage results in higher pregnancy rates per cycle, but also more multiple pregnancies. It now appears that transferring a single embryo at a later stage of in-vitro development (day 5) might lead to higher implantation rates, together with lowered multiple pregnancy rates, especially in women with a good prognosis. The philosophy is that by selecting women who are likely to have successful outcomes (because at least four eight-cell embryos of quality are achieved) and allowing for the development of their embryos to the blastocyst stage prior to implantation of single embryos, better clinical pregnancy rates could be achieved.
Whether such a policy in a large assisted conception unit would be feasible and give superior results is not known. To test the hypothesis, Khalaf et al (BJOG 2008;115:385-90) changed their guidelines and recorded their results for 18 months before and after the implementation of the new protocols. Despite only a selected group of patients fulfilling the criteria for single blastocyst transfer, they improved their clinical pregnancy rates from 27% to 32% while reducing their multiple pregnancy rates from 32% to 17%.
It is therefore feasible to use selective single embryo transfers in a busy IVF unit without sacrificing overall pregnancy rates and at the same time reducing twin and higher order multiple pregnancy risks. The policy had the extra spin-off of having more supernumerary embryos for cryopreservation and later use.
A Canadian study has found that singleton preterm babies and multiple birth babies have similar outcomes at the same gestational age, except for multiples having a greater predisposition to respiratory distress (Qui et al Obstet Gynecol 2008;111:365-71).
The extra costs of multiple pregnancies are considerable. As Wood points out (BJOG 2008;115:416) a twin pregnancy costs £1826 more than a low-risk singleton in antenatal and intrapartum care but other expenses have to be added in such as neonatal intensive care which could add another £3500 plus further infant in-patient care at £4800. These figures do not take into account other costs should complications arise like postnatal depression, a handicapped survivor never mind the emotional and societal costs of the stresses of ongoing care. A proper audit is indeed sobering.
Elective delivery of twins can safely include a vaginal option according to Schmitz et al who describe their experience in a French tertiary referral unit (Obstet Gynecol 2008;111:695-703). With an active intervention policy aimed at facilitating the delivery of the second twin about 5 minutes after the first, they had morbidity and mortality rates similar to those delivered by caesarean section.
