Researches from South Korea look at positions of twins in the womb and whether or not they change throughout the third trimester and delivery. The study was published in the journal Twin Research and Human Genetics. The journal publishes the results of a broad range of multiple birth research. The study looked at 411 women who gave birth to twins at 36 weeks or more. The researchers looked at whether or not the babies had changed their positions during early-third trimester and mid-third trimester. Early-third trimester was categorized as 28 to 31 weeks and mid-third trimester was categorized as 32 to 35 weeks.
Lower birth weight of twin A
In early-third trimester twin A – the twin closest to the cervix – had the same presentation at birth 87.6 percent of the time. 96.1 percent of the women had babies who maintained their presentation between mid-third trimester and birth. The only factor that contributed significantly to spontaneous version of twin A during mid-third trimester and delivery was a lower birth weight of twin A compared with twin B.
Non head-first presentation is unstable
The researchers concluded that if twin A is head first during the third trimester, it’s not likely to change at birth. They also came to the conclusion that head first presentation in twin pregnancies at early- and mid-third trimester is very predictable. In contrast, a non head-first presentation is relatively unstable.