We must make the distinction between monochorionic and dichorionic twins early on--optimally, in the first trimester.
In a dichorionic pregnancy, if a co-twin weighs 320 g at 26 weeks and is at high risk of in utero death, we typically would advise the parents to delay delivery.
Barrett reported on follow up at 34 weeks in 439 twins from the dichorionic
group and 183 from the monochononic group.
Physicians should spend some time assessing the thickness of the membrane, the lambda sign, and gender discord to differentiate between monochorionic and dichorionic
Although only 1% of singletons deliver before 32 weeks' gestation--the threshold below which profound damage becomes most likely--that's the case for 1 in 20 sets of dichorionic
twins, 1 in 10 sets of monochorionic twins, and 1 in 4 sets of triplets, Dr.
First-trimester ultrasound tip-offs that a twin pregnancy is dichorionic
and therefore not susceptible to back bleeding include the "twin peak" sign, discordant gender, and greater intertwin membrane thickness.
SAN FRANCISCO -- If you do fetal ultrasound scans, you've probably heard of the "twin peak" sign confirming that a set of twins is dichorionic
twins always have a membrane comprised of two chorions and two amnions that is four layers thick; on ultrasound it measures at least 2 mm thick.