A new RCT from Australia randomized 235 mothers carrying twins to be either delivered at 37 weeks gestation, or allowed to continue for at least another week (Dodd J, Crowther C, Haslam R, Robinson J, for the Twins Timing of Birth Trial G: Elective birth at 37 weeks of gestation versus standard care for women with an uncomplicated twin pregnancy at term: The twins timing of birth randomised trial. BJOG 2012, 119(8):964-974 http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0528.2012.03356.x/abstract).
The primary outcome variable was a composite of fetal/neonatal death or one of a number of serious morbidities, including asphyxia, immature lung disease, and fetal growth restriction ❤rd percentile. This is probably reasonable in general terms, but as with most composite outcomes the components are not of equivalent clinical importance, and clearly in this case are not mutually exclusive. A birth weight ❤rd centile is not of the same significance as asphyxia with encephalopathy.
Also, despite being a difficult trial that will most likely not be repeated, the power was not adequate to address the issue of respiratory distress and pulmonary hypertension as a result of cesarean section without labour at 37 weeks. They did not achieve the planned sample size, of about double the actual size, because of “lack of ongoing funding”. I can’t even tell from the article how many actually had a c/s without labour although half of the early delivery group (86% actually delivered between 37 weeks and 37 + 4 days, the rest before 38 weeks) had a labour induction, presumably the majority of the others had an elective section. As the serious respiratory complications are relatively uncommon, the study would have had to be much bigger to examine this effect.
However they did show that, if you wait and deliver most women after 38 weeks, twins aren’t growing very well at this point, and more of them fall below the 3rd %le, increasing from 3% in the early group to 10% in the “standard care” group. No consequences of being SGA, such as hypoglycemia are reported.
(of note there are a few irritating errors in the manuscript, including: the authors refer to stage 3 and stage 4 encephalopathy, and give the reference to Sarnat and Sarnat’s paper, which only describes 3 stages of course; the graph showing the distribution of gestational ages at delivery shows well over 100% of the early delivery mothers delivered before 38 weeks!).
The overall conclusion I guess is that there isn’t much obvious advantage to waiting until after 38 weeks to deliver twins, if you do you will have more babies fall below the 3rd %le. We could really have done with a much bigger trial that could have better addressed the respiratory risks, and focused on the mothers who did not get an induction, as having a trial of labour markedly reduces the respiratory consequences of being a little early, even if you are then delivered by c/s., but I won’t hold me breath for that to happen. We need some further very large observational studies to tell us a little more about those risks.
Finally you should note the frequency of assisted reproduction among the pregnancies, about 18% were the result of “assisted conception” a far higher rate than assisted conception among singletons, which is about 4% in Australia. They still have some way to go to control this adverse consequence of ART (although their latest report shows that they have been very effective at reducing the multiple pregnancy rate to about 8%), it is much worse in the rest of North America outside of Quebec the frequency of twins and tripets after IVF is about 30%. Here in Quebec we have reduced twin rates after ART from about 30% which is where we were a couple of years ago to under 5%. This can be done with a combination of government funding and strict regulation.