Podcast: Play in new window | Download
JA is a 33 year old woman, pregnant at 32 4/7 weeks with diamniotic, dichorionic twins who were conceived with IVF. She has been monitored with regular ultrasound scans, looking for normal growth. So far, everything has been fine, but at her last scan yesterday, the sonographer noticed new-onset discordant growth, primarily effecting twin B. Both the Abdominal Circumference and fetal femur length were significantly smaller than expected and significantly smaller than Twin A.
The sonographer then assessed the umbilical Doppler and found absent end-diastolic flow in Twin B.
Because of the discordant growth and evidence of significant flow impairment to Twin B, the decision was made to deliver her early. But to decrease the risk of prematurity, we elected to administer betamethasone to the mother, and continue to monitor the twins with daily NSTs. Once the 48 hours of steroid administration is up, we’ll perform a cesarean section, with Twin A in breech presentation, and Twin B in transverse lie.
In following twins, discordancy is a relatively common abnormality, with shunting of blood toward one twin at the expense of the other. This shunting is actually not very good for either twin, potentially leading to overload in one and hypovolemia in the other. This is in addition to the tendency for twins to experience symmetrical growth restriction due to two placentas competing within a single uterus.
One way to evaluate fetal blood flow is through Doppler studies. There is no way to non-invasively record the absolute blood flow through the umbilical arteries and vein, but we can indirectly measure the normalcy of the flow by comparing the ratio of the peak arterial flow to the end-diastolic flow. This should be between two and three to one. But as placental resistance increases, this ratio widens, with increased flow needed to penetrate the placenta, and significant end-diastolic back pressure. The most predictive findings, though, are the absence of end-diastolic flow, or the reversal of end-diastolic flow.
In the case of Twin B, the end-diastolic flow had diminished so much that it essentially ceased, indicating significant restriction to flow. That, in combination with the documented diminished growth of Twin B, leads us to deliver the twins early. However, the need for delivery, while important, is not urgent, allowing us the opportunity for improving fetal maturity with steroids.
