Placental Pathology in Twin Pregnancies
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Twin pregnancies remain a challenge in perinatal medicine, with significantly higher rates of complications and increased perinatal morbidity and mortality when compared to singletons. Abnormal growth in twins is a significant independent contributory factor to this increased morbidity, and knowledge of the underlying pathological processes governing growth disorders in twins is vital to improving our antenatal surveillance and clinical management of these pregnancies.
We performed a comprehensive study of the placental factors governing growth and development of twin pregnancies in a large, prospectively collected cohort of twins. Placental pathology was evaluated in terms of gross placental abnormalities and histopathological variants with further stereological studies then performed on a selected cohort of placentas.
The findings of this study emphasised the differing pathologies underlying disordered growth in monochorionic and dichorionic twin pregnancies.
Placentas of monochorionic twins with discordant growth and intrauterine growth restriction showed increased rates of gross abnormalities such as abnormalities of umbilical cord insertion. This likely reflects the unequal placental sharing that may lead to growth discordance among these twins.
In contrast, placentas from dichorionic twins with abnormal growth displayed histopathological features consistent with uteroplacental insufficiency.
The stereological studies of dichorionic twins further confirmed this with placentas from growth restricted dichorionic twins displaying a reduction in surface area and volume of terminal villi and capillaries.
In addition the stereological studies contrasting normal twins and normal singletons gave an interesting insight into the adaptive mechanisms at play to maintain growth in multiple pregnancies.
The findings of this study reinforce the importance of accurate assessment of chorionicity in twins, targeted ultrasound assessment including evaluation of placental cord insertion and selected use of multi-vessel Doppler studies to evaluate fetal well-being as part of antenatal ultrasound surveillance.