Here's a good little explanation
New Approach to Risk Assessment in Twins.
OB/GYN News, May 1, 2001, by Bruce JancinContinued from page 1
Discordant growth, defined as at least a 20% difference in fetal weight, occurs in 15%-30% of twins. Textbooks state that this is a serious cause for concern. But a recent University of Colorado study of 102 twin pregnancies suggests the situation isn't so black and white.
The study showed, surprisingly, that the only patients who got into trouble were those with discordant growth in which one fetus was small for gestarional age (SGA), and the other wasn't. They delivered at a mean of 33.75 weeks' gestation, compared with 36.5 weeks for the overall group. Again, the subgroup with two SGA fetuses actually had the greatest gestational age of all at delivery.
With length of stay in the neonatal nursery as a proxy for health status at delivery, it was interesting to note that SGA babies from discordant-growth pregnancies had an average stay of 25 days, while SGA babies from pregnancies in which both babies were SGA stayed only one-quarter as long, Dr. Hobbins continued.
In another Colorado study, 24 women with growth-discordant twin pregnancies underwent serial ultrasound evaluation. Those in whom the discordance was detected before 30 weeks delivered at a mean gestational age of 33.4 weeks, compared with 35.5 weeks when growth discordance showed up only later in pregnancy Small babies with early growth discordance stayed a mean of 40 days in the newborn nursery compared with 19 days for those who showed growth discordance only after 30 weeks.
Early growth discordance was typically associated with a substantially less lush placenta on the side of the smaller twin. These fetuses also demonstrate significantly lower average and peak blood flows through the umbilical vein, according to Doppler ultrasound studies by Dr. Hobbins and coinvestigators at the University of Milan.
"One twin is in trouble, the other is an innocent bystander. It raises an ethical question sometimes of when to deliver," he said.
The underlying idea behind this early ultrasound assessment is that when physicians see these abnormalities, they can intensify their surveillance in an effort to precisely time delivery to diminish the chance of neurologic sequeli, he explained.
"The more we look at this, the more it looks like the converse is true," Dr. Hobbins added. "If you don't have a short cervix, if you don't have twin-to-twin discordance early on, and if the placentas look equally lush, you're going to be able to leave these people alone and just let them have a nice pregnancy instead of what we wind up doing now, which is just studying the heck out of them."
COPYRIGHT 2001 International Medical News Group