Factors affecting fetal presentation in twin pregnancies across gestation
Nathan S Fox1, Andrei Rebarber, Henry N Lesser
1Department of Obstetrics, Gynecology, and Reproductive Science, Mount Sinai School of Medicine , New York, NY , USA .
Objective:
To describe pregnancy characteristics associated with the occurrence of spontaneous version in twin pregnancies from 20 weeks until delivery.
Study Design:
Review of ultrasound and pregnancy data for all twin pregnancies delivered >24 weeks by one Maternal-Fetal Medicine practice from June 2005-May 2012. For each 4-week gestational age window, fetal presentations were recorded, as well as the likelihood of the final presentation being vertex for Twin A and vertex for both twins. Case-control analysis was performed to estimate associations between pregnancy characteristics and spontaneous version of Twin A.
Results:
A total of 491 twin pregnancies were included. The distribution of fetal presentations changed significantly from 20 weeks to delivery, but the presentation at each gestational age interval was significantly associated with the final position of Twin A and the likelihood of vertex-vertex presentation at delivery. The likelihood of spontaneous version of Twin A decreased from 27.9% after 24-27 6/7 weeks, to 18.8% after 28-31 6/7 weeks, to 8.2% after 32-35 6/7 weeks. Pregnancy characteristics associated with spontaneous version of Twin A were a prior vaginal delivery and increased fetal size of either twin.
Conclusions:
The likelihood of spontaneous version of Twin A decreases as pregnancy advances. Parity and increased fetal size are associated with spontaneous version.
Related Concept Videos
Teratogenicity
Fetal Circulation
Two umbilical arteries transport blood from the fetus to the placenta. At the placenta, the blood absorbs oxygen and nutrients while simultaneously eliminating waste products. This oxygen-enriched and nutrient-rich blood then returns to the fetus through one...
Factors Affecting Drug Distribution: Miscellaneous Factors
Age plays a significant role due to differences in body composition among different age groups. Infants, for instance, have a higher proportion of total body water and lower albumin levels, a protein that binds drugs in the bloodstream. This unique composition in infants enhances the...
Factors Affecting Drug Response: Overview
Factors Affecting Drug Distribution: Physiological Barriers
The capillary endothelial barrier allows only smaller molecules below 600 Da (Daltons) to pass through. It also restricts drugs like heparin that are bound to blood components, limiting their movement within the bloodstream.
The...
Ovarian Cycle

