Predictie van uitkomst bij monochoriale tweelingzwangerschappen

Monochorionic diamniotic (MCDA) twin pregnancies are especially high-risk because they share a placenta and are connected by vascular anastomoses. Despite our growing understanding of MCDA pregnancies, their mortality and morbidity remain higher compared to dichorionic twins and singletons. This thesis aimed to investigate possible predictors of adverse outcomes in the MCDA population in general and in cases complicated by selective fetal growth restriction (sFGR) in particular, as well as gaining insight into placental sharing. We did so by performing cohort studies in MCDA twins recruited in the first trimester and by performing placental injection studies. Our cohort studies in the general population show that a velamentous cord insertion in one twin is associated with adverse outcomes and twin-twin transfusion syndrome (TTTS). sFGR on the other hand, is associated with both discordance in insertion sites and velamentous cord insertion in one twin. Also, MCDA twins conceived after in vitro fertilization or intracytoplasmic sperm injection have lower overall survival rates and higher rates of second-trimester miscarriage than spontaneously conceived MCDA twins. Finally, fortnightly ultrasound scans from 16 weeks onward detect 9 out of 10 TTTS pregnancies in time. Most stage III-IV cases have abnormal Doppler findings before diagnosis, and most stage V cases present outside the typical time window of 16 and 26 weeks. Survival rates after laser therapy underestimate the true mortality of TTTS. Specifically, for sFGR, isolated cases have a 90% survival rate. However, the subsequent development of TTTS, absent or reversed end-diastolic flow in the umbilical artery of the smaller twin, and the presence of a major anomaly adversely affect survival. However, even with abnormal Doppler, the survival rate after 20 weeks is more than 90%. As for the prenatal classification sFGR, the documentation of an artery-to-artery anastomosis, signs of cardiac strain in the large twin, and proximate cord insertions seem specific for Type III sFGR. In contrast, placental dichotomy and a more severe growth restriction are typically seen in Type II. We developed a new technique to assess placental sharing using an X-ray angiogram, which appeared to be slightly more accurate than the classic technique. Next, we confirmed that the vascular equator is located in the middle between both cord insertions in concordant placentas. In intermediate and discordant placentas, the equator is closer to the more central cord insertion. Umbilical vein parameters on prenatal ultrasound are associated with placental sharing. Additionally, the flow in the umbilical vein is associated with fetal demise at 16, 20, and 28 weeks. Finally, vein-to-vein anastomoses appear to decrease the birth weight discordance relative to the placental sharing discordance, independent of the artery-to-artery anastomoses. To conclude, our research has provided information on the outcome of MCDA twin pregnancies that is valuable for both clinicians and future parents. We have also demonstrated a link between several ultrasound variables and placental sharing, both in the general MCDA twin population and in sFGR in particular.

Publication year:2021

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